// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! # Debug Info Module
//!
//! This module serves the purpose of generating debug symbols. We use LLVM's
//! [source level debugging](http://llvm.org/docs/SourceLevelDebugging.html)
//! features for generating the debug information. The general principle is this:
//!
//! Given the right metadata in the LLVM IR, the LLVM code generator is able to
//! create DWARF debug symbols for the given code. The
//! [metadata](http://llvm.org/docs/LangRef.html#metadata-type) is structured much
//! like DWARF *debugging information entries* (DIE), representing type information
//! such as datatype layout, function signatures, block layout, variable location
//! and scope information, etc. It is the purpose of this module to generate correct
//! metadata and insert it into the LLVM IR.
//!
//! As the exact format of metadata trees may change between different LLVM
//! versions, we now use LLVM
//! [DIBuilder](http://llvm.org/docs/doxygen/html/classllvm_1_1DIBuilder.html) to
//! create metadata where possible. This will hopefully ease the adaption of this
//! module to future LLVM versions.
//!
//! The public API of the module is a set of functions that will insert the correct
//! metadata into the LLVM IR when called with the right parameters. The module is
//! thus driven from an outside client with functions like
//! `debuginfo::create_local_var_metadata(bcx: block, local: &ast::local)`.
//!
//! Internally the module will try to reuse already created metadata by utilizing a
//! cache. The way to get a shared metadata node when needed is thus to just call
//! the corresponding function in this module:
//!
//!     let file_metadata = file_metadata(crate_context, path);
//!
//! The function will take care of probing the cache for an existing node for that
//! exact file path.
//!
//! All private state used by the module is stored within either the
//! CrateDebugContext struct (owned by the CrateContext) or the FunctionDebugContext
//! (owned by the FunctionContext).
//!
//! This file consists of three conceptual sections:
//! 1. The public interface of the module
//! 2. Module-internal metadata creation functions
//! 3. Minor utility functions
//!
//!
//! ## Recursive Types
//!
//! Some kinds of types, such as structs and enums can be recursive. That means that
//! the type definition of some type X refers to some other type which in turn
//! (transitively) refers to X. This introduces cycles into the type referral graph.
//! A naive algorithm doing an on-demand, depth-first traversal of this graph when
//! describing types, can get trapped in an endless loop when it reaches such a
//! cycle.
//!
//! For example, the following simple type for a singly-linked list...
//!
//! ```
//! struct List {
//!     value: int,
//!     tail: Option<Box<List>>,
//! }
//! ```
//!
//! will generate the following callstack with a naive DFS algorithm:
//!
//! ```
//! describe(t = List)
//!   describe(t = int)
//!   describe(t = Option<Box<List>>)
//!     describe(t = Box<List>)
//!       describe(t = List) // at the beginning again...
//!       ...
//! ```
//!
//! To break cycles like these, we use "forward declarations". That is, when the
//! algorithm encounters a possibly recursive type (any struct or enum), it
//! immediately creates a type description node and inserts it into the cache
//! *before* describing the members of the type. This type description is just a
//! stub (as type members are not described and added to it yet) but it allows the
//! algorithm to already refer to the type. After the stub is inserted into the
//! cache, the algorithm continues as before. If it now encounters a recursive
//! reference, it will hit the cache and does not try to describe the type anew.
//!
//! This behaviour is encapsulated in the 'RecursiveTypeDescription' enum, which
//! represents a kind of continuation, storing all state needed to continue
//! traversal at the type members after the type has been registered with the cache.
//! (This implementation approach might be a tad over-engineered and may change in
//! the future)
//!
//!
//! ## Source Locations and Line Information
//!
//! In addition to data type descriptions the debugging information must also allow
//! to map machine code locations back to source code locations in order to be useful.
//! This functionality is also handled in this module. The following functions allow
//! to control source mappings:
//!
//! + set_source_location()
//! + clear_source_location()
//! + start_emitting_source_locations()
//!
//! `set_source_location()` allows to set the current source location. All IR
//! instructions created after a call to this function will be linked to the given
//! source location, until another location is specified with
//! `set_source_location()` or the source location is cleared with
//! `clear_source_location()`. In the later case, subsequent IR instruction will not
//! be linked to any source location. As you can see, this is a stateful API
//! (mimicking the one in LLVM), so be careful with source locations set by previous
//! calls. It's probably best to not rely on any specific state being present at a
//! given point in code.
//!
//! One topic that deserves some extra attention is *function prologues*. At the
//! beginning of a function's machine code there are typically a few instructions
//! for loading argument values into allocas and checking if there's enough stack
//! space for the function to execute. This *prologue* is not visible in the source
//! code and LLVM puts a special PROLOGUE END marker into the line table at the
//! first non-prologue instruction of the function. In order to find out where the
//! prologue ends, LLVM looks for the first instruction in the function body that is
//! linked to a source location. So, when generating prologue instructions we have
//! to make sure that we don't emit source location information until the 'real'
//! function body begins. For this reason, source location emission is disabled by
//! default for any new function being translated and is only activated after a call
//! to the third function from the list above, `start_emitting_source_locations()`.
//! This function should be called right before regularly starting to translate the
//! top-level block of the given function.
//!
//! There is one exception to the above rule: `llvm.dbg.declare` instruction must be
//! linked to the source location of the variable being declared. For function
//! parameters these `llvm.dbg.declare` instructions typically occur in the middle
//! of the prologue, however, they are ignored by LLVM's prologue detection. The
//! `create_argument_metadata()` and related functions take care of linking the
//! `llvm.dbg.declare` instructions to the correct source locations even while
//! source location emission is still disabled, so there is no need to do anything
//! special with source location handling here.
//!
//! ## Unique Type Identification
//!
//! In order for link-time optimization to work properly, LLVM needs a unique type
//! identifier that tells it across compilation units which types are the same as
//! others. This type identifier is created by TypeMap::get_unique_type_id_of_type()
//! using the following algorithm:
//!
//! (1) Primitive types have their name as ID
//! (2) Structs, enums and traits have a multipart identifier
//!
//!     (1) The first part is the SVH (strict version hash) of the crate they were
//!         originally defined in
//!
//!     (2) The second part is the ast::NodeId of the definition in their original
//!         crate
//!
//!     (3) The final part is a concatenation of the type IDs of their concrete type
//!         arguments if they are generic types.
//!
//! (3) Tuple-, pointer and function types are structurally identified, which means
//!     that they are equivalent if their component types are equivalent (i.e. (int,
//!     int) is the same regardless in which crate it is used).
//!
//! This algorithm also provides a stable ID for types that are defined in one crate
//! but instantiated from metadata within another crate. We just have to take care
//! to always map crate and node IDs back to the original crate context.
//!
//! As a side-effect these unique type IDs also help to solve a problem arising from
//! lifetime parameters. Since lifetime parameters are completely omitted in
//! debuginfo, more than one `Ty` instance may map to the same debuginfo type
//! metadata, that is, some struct `Struct<'a>` may have N instantiations with
//! different concrete substitutions for `'a`, and thus there will be N `Ty`
//! instances for the type `Struct<'a>` even though it is not generic otherwise.
//! Unfortunately this means that we cannot use `ty::type_id()` as cheap identifier
//! for type metadata---we have done this in the past, but it led to unnecessary
//! metadata duplication in the best case and LLVM assertions in the worst. However,
//! the unique type ID as described above *can* be used as identifier. Since it is
//! comparatively expensive to construct, though, `ty::type_id()` is still used
//! additionally as an optimization for cases where the exact same type has been
//! seen before (which is most of the time).
use self::VariableAccess::*;
use self::VariableKind::*;
use self::MemberOffset::*;
use self::MemberDescriptionFactory::*;
use self::RecursiveTypeDescription::*;
use self::EnumDiscriminantInfo::*;
use self::InternalDebugLocation::*;

use llvm;
use llvm::{ModuleRef, ContextRef, ValueRef};
use llvm::debuginfo::*;
use metadata::csearch;
use middle::subst::{self, Substs};
use trans::{self, adt, machine, type_of};
use trans::common::{self, NodeIdAndSpan, CrateContext, FunctionContext, Block,
                    C_bytes, NormalizingClosureTyper};
use trans::_match::{BindingInfo, TrByCopy, TrByMove, TrByRef};
use trans::monomorphize;
use trans::type_::Type;
use middle::ty::{self, Ty, ClosureTyper};
use middle::pat_util;
use session::config::{self, FullDebugInfo, LimitedDebugInfo, NoDebugInfo};
use util::nodemap::{DefIdMap, NodeMap, FnvHashMap, FnvHashSet};
use util::ppaux;
use util::common::path2cstr;

use libc::{c_uint, c_longlong};
use std::cell::{Cell, RefCell};
use std::ffi::CString;
use std::path::Path;
use std::ptr;
use std::rc::{Rc, Weak};
use syntax::util::interner::Interner;
use syntax::codemap::{Span, Pos};
use syntax::{ast, codemap, ast_util, ast_map, attr};
use syntax::parse::token::{self, special_idents};

const DW_LANG_RUST: c_uint = 0x9000;

#[allow(non_upper_case_globals)]
const DW_TAG_auto_variable: c_uint = 0x100;
#[allow(non_upper_case_globals)]
const DW_TAG_arg_variable: c_uint = 0x101;

#[allow(non_upper_case_globals)]
const DW_ATE_boolean: c_uint = 0x02;
#[allow(non_upper_case_globals)]
const DW_ATE_float: c_uint = 0x04;
#[allow(non_upper_case_globals)]
const DW_ATE_signed: c_uint = 0x05;
#[allow(non_upper_case_globals)]
const DW_ATE_unsigned: c_uint = 0x07;
#[allow(non_upper_case_globals)]
const DW_ATE_unsigned_char: c_uint = 0x08;

const UNKNOWN_LINE_NUMBER: c_uint = 0;
const UNKNOWN_COLUMN_NUMBER: c_uint = 0;

// ptr::null() doesn't work :(
const UNKNOWN_FILE_METADATA: DIFile = (0 as DIFile);
const UNKNOWN_SCOPE_METADATA: DIScope = (0 as DIScope);

const FLAGS_NONE: c_uint = 0;

//=-----------------------------------------------------------------------------
//  Public Interface of debuginfo module
//=-----------------------------------------------------------------------------

#[derive(Copy, Debug, Hash, Eq, PartialEq, Clone)]
struct UniqueTypeId(ast::Name);

// The TypeMap is where the CrateDebugContext holds the type metadata nodes
// created so far. The metadata nodes are indexed by UniqueTypeId, and, for
// faster lookup, also by Ty. The TypeMap is responsible for creating
// UniqueTypeIds.
struct TypeMap<'tcx> {
    // The UniqueTypeIds created so far
    unique_id_interner: Interner<Rc<String>>,
    // A map from UniqueTypeId to debuginfo metadata for that type. This is a 1:1 mapping.
    unique_id_to_metadata: FnvHashMap<UniqueTypeId, DIType>,
    // A map from types to debuginfo metadata. This is a N:1 mapping.
    type_to_metadata: FnvHashMap<Ty<'tcx>, DIType>,
    // A map from types to UniqueTypeId. This is a N:1 mapping.
    type_to_unique_id: FnvHashMap<Ty<'tcx>, UniqueTypeId>
}

impl<'tcx> TypeMap<'tcx> {

    fn new() -> TypeMap<'tcx> {
        TypeMap {
            unique_id_interner: Interner::new(),
            type_to_metadata: FnvHashMap(),
            unique_id_to_metadata: FnvHashMap(),
            type_to_unique_id: FnvHashMap(),
        }
    }

    // Adds a Ty to metadata mapping to the TypeMap. The method will fail if
    // the mapping already exists.
    fn register_type_with_metadata<'a>(&mut self,
                                       cx: &CrateContext<'a, 'tcx>,
                                       type_: Ty<'tcx>,
                                       metadata: DIType) {
        if self.type_to_metadata.insert(type_, metadata).is_some() {
            cx.sess().bug(&format!("Type metadata for Ty '{}' is already in the TypeMap!",
                                   ppaux::ty_to_string(cx.tcx(), type_)));
        }
    }

    // Adds a UniqueTypeId to metadata mapping to the TypeMap. The method will
    // fail if the mapping already exists.
    fn register_unique_id_with_metadata(&mut self,
                                        cx: &CrateContext,
                                        unique_type_id: UniqueTypeId,
                                        metadata: DIType) {
        if self.unique_id_to_metadata.insert(unique_type_id, metadata).is_some() {
            let unique_type_id_str = self.get_unique_type_id_as_string(unique_type_id);
            cx.sess().bug(&format!("Type metadata for unique id '{}' is already in the TypeMap!",
                                  &unique_type_id_str[..]));
        }
    }

    fn find_metadata_for_type(&self, type_: Ty<'tcx>) -> Option<DIType> {
        self.type_to_metadata.get(&type_).cloned()
    }

    fn find_metadata_for_unique_id(&self, unique_type_id: UniqueTypeId) -> Option<DIType> {
        self.unique_id_to_metadata.get(&unique_type_id).cloned()
    }

    // Get the string representation of a UniqueTypeId. This method will fail if
    // the id is unknown.
    fn get_unique_type_id_as_string(&self, unique_type_id: UniqueTypeId) -> Rc<String> {
        let UniqueTypeId(interner_key) = unique_type_id;
        self.unique_id_interner.get(interner_key)
    }

    // Get the UniqueTypeId for the given type. If the UniqueTypeId for the given
    // type has been requested before, this is just a table lookup. Otherwise an
    // ID will be generated and stored for later lookup.
    fn get_unique_type_id_of_type<'a>(&mut self, cx: &CrateContext<'a, 'tcx>,
                                      type_: Ty<'tcx>) -> UniqueTypeId {

        // basic type           -> {:name of the type:}
        // tuple                -> {tuple_(:param-uid:)*}
        // struct               -> {struct_:svh: / :node-id:_<(:param-uid:),*> }
        // enum                 -> {enum_:svh: / :node-id:_<(:param-uid:),*> }
        // enum variant         -> {variant_:variant-name:_:enum-uid:}
        // reference (&)        -> {& :pointee-uid:}
        // mut reference (&mut) -> {&mut :pointee-uid:}
        // ptr (*)              -> {* :pointee-uid:}
        // mut ptr (*mut)       -> {*mut :pointee-uid:}
        // unique ptr (~)       -> {~ :pointee-uid:}
        // @-ptr (@)            -> {@ :pointee-uid:}
        // sized vec ([T; x])   -> {[:size:] :element-uid:}
        // unsized vec ([T])    -> {[] :element-uid:}
        // trait (T)            -> {trait_:svh: / :node-id:_<(:param-uid:),*> }
        // closure              -> {<unsafe_> <once_> :store-sigil: |(:param-uid:),* <,_...>| -> \
        //                             :return-type-uid: : (:bounds:)*}
        // function             -> {<unsafe_> <abi_> fn( (:param-uid:)* <,_...> ) -> \
        //                             :return-type-uid:}
        // unique vec box (~[]) -> {HEAP_VEC_BOX<:pointee-uid:>}
        // gc box               -> {GC_BOX<:pointee-uid:>}

        match self.type_to_unique_id.get(&type_).cloned() {
            Some(unique_type_id) => return unique_type_id,
            None => { /* generate one */}
        };

        let mut unique_type_id = String::with_capacity(256);
        unique_type_id.push('{');

        match type_.sty {
            ty::ty_bool     |
            ty::ty_char     |
            ty::ty_str      |
            ty::ty_int(_)   |
            ty::ty_uint(_)  |
            ty::ty_float(_) => {
                push_debuginfo_type_name(cx, type_, false, &mut unique_type_id);
            },
            ty::ty_enum(def_id, substs) => {
                unique_type_id.push_str("enum ");
                from_def_id_and_substs(self, cx, def_id, substs, &mut unique_type_id);
            },
            ty::ty_struct(def_id, substs) => {
                unique_type_id.push_str("struct ");
                from_def_id_and_substs(self, cx, def_id, substs, &mut unique_type_id);
            },
            ty::ty_tup(ref component_types) if component_types.is_empty() => {
                push_debuginfo_type_name(cx, type_, false, &mut unique_type_id);
            },
            ty::ty_tup(ref component_types) => {
                unique_type_id.push_str("tuple ");
                for &component_type in component_types {
                    let component_type_id =
                        self.get_unique_type_id_of_type(cx, component_type);
                    let component_type_id =
                        self.get_unique_type_id_as_string(component_type_id);
                    unique_type_id.push_str(&component_type_id[..]);
                }
            },
            ty::ty_uniq(inner_type) => {
                unique_type_id.push('~');
                let inner_type_id = self.get_unique_type_id_of_type(cx, inner_type);
                let inner_type_id = self.get_unique_type_id_as_string(inner_type_id);
                unique_type_id.push_str(&inner_type_id[..]);
            },
            ty::ty_ptr(ty::mt { ty: inner_type, mutbl } ) => {
                unique_type_id.push('*');
                if mutbl == ast::MutMutable {
                    unique_type_id.push_str("mut");
                }

                let inner_type_id = self.get_unique_type_id_of_type(cx, inner_type);
                let inner_type_id = self.get_unique_type_id_as_string(inner_type_id);
                unique_type_id.push_str(&inner_type_id[..]);
            },
            ty::ty_rptr(_, ty::mt { ty: inner_type, mutbl }) => {
                unique_type_id.push('&');
                if mutbl == ast::MutMutable {
                    unique_type_id.push_str("mut");
                }

                let inner_type_id = self.get_unique_type_id_of_type(cx, inner_type);
                let inner_type_id = self.get_unique_type_id_as_string(inner_type_id);
                unique_type_id.push_str(&inner_type_id[..]);
            },
            ty::ty_vec(inner_type, optional_length) => {
                match optional_length {
                    Some(len) => {
                        unique_type_id.push_str(&format!("[{}]", len));
                    }
                    None => {
                        unique_type_id.push_str("[]");
                    }
                };

                let inner_type_id = self.get_unique_type_id_of_type(cx, inner_type);
                let inner_type_id = self.get_unique_type_id_as_string(inner_type_id);
                unique_type_id.push_str(&inner_type_id[..]);
            },
            ty::ty_trait(ref trait_data) => {
                unique_type_id.push_str("trait ");

                let principal =
                    ty::erase_late_bound_regions(cx.tcx(),
                                                 &trait_data.principal);

                from_def_id_and_substs(self,
                                       cx,
                                       principal.def_id,
                                       principal.substs,
                                       &mut unique_type_id);
            },
            ty::ty_bare_fn(_, &ty::BareFnTy{ unsafety, abi, ref sig } ) => {
                if unsafety == ast::Unsafety::Unsafe {
                    unique_type_id.push_str("unsafe ");
                }

                unique_type_id.push_str(abi.name());

                unique_type_id.push_str(" fn(");

                let sig = ty::erase_late_bound_regions(cx.tcx(), sig);

                for &parameter_type in &sig.inputs {
                    let parameter_type_id =
                        self.get_unique_type_id_of_type(cx, parameter_type);
                    let parameter_type_id =
                        self.get_unique_type_id_as_string(parameter_type_id);
                    unique_type_id.push_str(&parameter_type_id[..]);
                    unique_type_id.push(',');
                }

                if sig.variadic {
                    unique_type_id.push_str("...");
                }

                unique_type_id.push_str(")->");
                match sig.output {
                    ty::FnConverging(ret_ty) => {
                        let return_type_id = self.get_unique_type_id_of_type(cx, ret_ty);
                        let return_type_id = self.get_unique_type_id_as_string(return_type_id);
                        unique_type_id.push_str(&return_type_id[..]);
                    }
                    ty::FnDiverging => {
                        unique_type_id.push_str("!");
                    }
                }
            },
            ty::ty_closure(def_id, substs) => {
                let typer = NormalizingClosureTyper::new(cx.tcx());
                let closure_ty = typer.closure_type(def_id, substs);
                self.get_unique_type_id_of_closure_type(cx,
                                                        closure_ty,
                                                        &mut unique_type_id);
            },
            _ => {
                cx.sess().bug(&format!("get_unique_type_id_of_type() - unexpected type: {}, {:?}",
                                      &ppaux::ty_to_string(cx.tcx(), type_),
                                      type_.sty))
            }
        };

        unique_type_id.push('}');

        // Trim to size before storing permanently
        unique_type_id.shrink_to_fit();

        let key = self.unique_id_interner.intern(Rc::new(unique_type_id));
        self.type_to_unique_id.insert(type_, UniqueTypeId(key));

        return UniqueTypeId(key);

        fn from_def_id_and_substs<'a, 'tcx>(type_map: &mut TypeMap<'tcx>,
                                            cx: &CrateContext<'a, 'tcx>,
                                            def_id: ast::DefId,
                                            substs: &subst::Substs<'tcx>,
                                            output: &mut String) {
            // First, find out the 'real' def_id of the type. Items inlined from
            // other crates have to be mapped back to their source.
            let source_def_id = if def_id.krate == ast::LOCAL_CRATE {
                match cx.external_srcs().borrow().get(&def_id.node).cloned() {
                    Some(source_def_id) => {
                        // The given def_id identifies the inlined copy of a
                        // type definition, let's take the source of the copy.
                        source_def_id
                    }
                    None => def_id
                }
            } else {
                def_id
            };

            // Get the crate hash as first part of the identifier.
            let crate_hash = if source_def_id.krate == ast::LOCAL_CRATE {
                cx.link_meta().crate_hash.clone()
            } else {
                cx.sess().cstore.get_crate_hash(source_def_id.krate)
            };

            output.push_str(crate_hash.as_str());
            output.push_str("/");
            output.push_str(&format!("{:x}", def_id.node));

            // Maybe check that there is no self type here.

            let tps = substs.types.get_slice(subst::TypeSpace);
            if tps.len() > 0 {
                output.push('<');

                for &type_parameter in tps {
                    let param_type_id =
                        type_map.get_unique_type_id_of_type(cx, type_parameter);
                    let param_type_id =
                        type_map.get_unique_type_id_as_string(param_type_id);
                    output.push_str(&param_type_id[..]);
                    output.push(',');
                }

                output.push('>');
            }
        }
    }

    fn get_unique_type_id_of_closure_type<'a>(&mut self,
                                              cx: &CrateContext<'a, 'tcx>,
                                              closure_ty: ty::ClosureTy<'tcx>,
                                              unique_type_id: &mut String) {
        let ty::ClosureTy { unsafety,
                            ref sig,
                            abi: _ } = closure_ty;

        if unsafety == ast::Unsafety::Unsafe {
            unique_type_id.push_str("unsafe ");
        }

        unique_type_id.push_str("|");

        let sig = ty::erase_late_bound_regions(cx.tcx(), sig);

        for &parameter_type in &sig.inputs {
            let parameter_type_id =
                self.get_unique_type_id_of_type(cx, parameter_type);
            let parameter_type_id =
                self.get_unique_type_id_as_string(parameter_type_id);
            unique_type_id.push_str(&parameter_type_id[..]);
            unique_type_id.push(',');
        }

        if sig.variadic {
            unique_type_id.push_str("...");
        }

        unique_type_id.push_str("|->");

        match sig.output {
            ty::FnConverging(ret_ty) => {
                let return_type_id = self.get_unique_type_id_of_type(cx, ret_ty);
                let return_type_id = self.get_unique_type_id_as_string(return_type_id);
                unique_type_id.push_str(&return_type_id[..]);
            }
            ty::FnDiverging => {
                unique_type_id.push_str("!");
            }
        }
    }

    // Get the UniqueTypeId for an enum variant. Enum variants are not really
    // types of their own, so they need special handling. We still need a
    // UniqueTypeId for them, since to debuginfo they *are* real types.
    fn get_unique_type_id_of_enum_variant<'a>(&mut self,
                                              cx: &CrateContext<'a, 'tcx>,
                                              enum_type: Ty<'tcx>,
                                              variant_name: &str)
                                              -> UniqueTypeId {
        let enum_type_id = self.get_unique_type_id_of_type(cx, enum_type);
        let enum_variant_type_id = format!("{}::{}",
                                           &self.get_unique_type_id_as_string(enum_type_id),
                                           variant_name);
        let interner_key = self.unique_id_interner.intern(Rc::new(enum_variant_type_id));
        UniqueTypeId(interner_key)
    }
}

// Returns from the enclosing function if the type metadata with the given
// unique id can be found in the type map
macro_rules! return_if_metadata_created_in_meantime {
    ($cx: expr, $unique_type_id: expr) => (
        match debug_context($cx).type_map
                                .borrow()
                                .find_metadata_for_unique_id($unique_type_id) {
            Some(metadata) => return MetadataCreationResult::new(metadata, true),
            None => { /* proceed normally */ }
        };
    )
}


/// A context object for maintaining all state needed by the debuginfo module.
pub struct CrateDebugContext<'tcx> {
    llcontext: ContextRef,
    builder: DIBuilderRef,
    current_debug_location: Cell<InternalDebugLocation>,
    created_files: RefCell<FnvHashMap<String, DIFile>>,
    created_enum_disr_types: RefCell<DefIdMap<DIType>>,

    type_map: RefCell<TypeMap<'tcx>>,
    namespace_map: RefCell<FnvHashMap<Vec<ast::Name>, Rc<NamespaceTreeNode>>>,

    // This collection is used to assert that composite types (structs, enums,
    // ...) have their members only set once:
    composite_types_completed: RefCell<FnvHashSet<DIType>>,
}

impl<'tcx> CrateDebugContext<'tcx> {
    pub fn new(llmod: ModuleRef) -> CrateDebugContext<'tcx> {
        debug!("CrateDebugContext::new");
        let builder = unsafe { llvm::LLVMDIBuilderCreate(llmod) };
        // DIBuilder inherits context from the module, so we'd better use the same one
        let llcontext = unsafe { llvm::LLVMGetModuleContext(llmod) };
        return CrateDebugContext {
            llcontext: llcontext,
            builder: builder,
            current_debug_location: Cell::new(UnknownLocation),
            created_files: RefCell::new(FnvHashMap()),
            created_enum_disr_types: RefCell::new(DefIdMap()),
            type_map: RefCell::new(TypeMap::new()),
            namespace_map: RefCell::new(FnvHashMap()),
            composite_types_completed: RefCell::new(FnvHashSet()),
        };
    }
}

pub enum FunctionDebugContext {
    RegularContext(Box<FunctionDebugContextData>),
    DebugInfoDisabled,
    FunctionWithoutDebugInfo,
}

impl FunctionDebugContext {
    fn get_ref<'a>(&'a self,
                   cx: &CrateContext,
                   span: Span)
                   -> &'a FunctionDebugContextData {
        match *self {
            FunctionDebugContext::RegularContext(box ref data) => data,
            FunctionDebugContext::DebugInfoDisabled => {
                cx.sess().span_bug(span,
                                   FunctionDebugContext::debuginfo_disabled_message());
            }
            FunctionDebugContext::FunctionWithoutDebugInfo => {
                cx.sess().span_bug(span,
                                   FunctionDebugContext::should_be_ignored_message());
            }
        }
    }

    fn debuginfo_disabled_message() -> &'static str {
        "debuginfo: Error trying to access FunctionDebugContext although debug info is disabled!"
    }

    fn should_be_ignored_message() -> &'static str {
        "debuginfo: Error trying to access FunctionDebugContext for function that should be \
         ignored by debug info!"
    }
}

struct FunctionDebugContextData {
    scope_map: RefCell<NodeMap<DIScope>>,
    fn_metadata: DISubprogram,
    argument_counter: Cell<usize>,
    source_locations_enabled: Cell<bool>,
    source_location_override: Cell<bool>,
}

enum VariableAccess<'a> {
    // The llptr given is an alloca containing the variable's value
    DirectVariable { alloca: ValueRef },
    // The llptr given is an alloca containing the start of some pointer chain
    // leading to the variable's content.
    IndirectVariable { alloca: ValueRef, address_operations: &'a [i64] }
}

enum VariableKind {
    ArgumentVariable(usize /*index*/),
    LocalVariable,
    CapturedVariable,
}

/// Create any deferred debug metadata nodes
pub fn finalize(cx: &CrateContext) {
    if cx.dbg_cx().is_none() {
        return;
    }

    debug!("finalize");
    let _ = compile_unit_metadata(cx);

    if needs_gdb_debug_scripts_section(cx) {
        // Add a .debug_gdb_scripts section to this compile-unit. This will
        // cause GDB to try and load the gdb_load_rust_pretty_printers.py file,
        // which activates the Rust pretty printers for binary this section is
        // contained in.
        get_or_insert_gdb_debug_scripts_section_global(cx);
    }

    unsafe {
        llvm::LLVMDIBuilderFinalize(DIB(cx));
        llvm::LLVMDIBuilderDispose(DIB(cx));
        // Debuginfo generation in LLVM by default uses a higher
        // version of dwarf than OS X currently understands. We can
        // instruct LLVM to emit an older version of dwarf, however,
        // for OS X to understand. For more info see #11352
        // This can be overridden using --llvm-opts -dwarf-version,N.
        // Android has the same issue (#22398)
        if cx.sess().target.target.options.is_like_osx ||
           cx.sess().target.target.options.is_like_android {
            llvm::LLVMRustAddModuleFlag(cx.llmod(),
                                        "Dwarf Version\0".as_ptr() as *const _,
                                        2)
        }

        // Prevent bitcode readers from deleting the debug info.
        let ptr = "Debug Info Version\0".as_ptr();
        llvm::LLVMRustAddModuleFlag(cx.llmod(), ptr as *const _,
                                    llvm::LLVMRustDebugMetadataVersion);
    };
}

/// Creates debug information for the given global variable.
///
/// Adds the created metadata nodes directly to the crate's IR.
pub fn create_global_var_metadata(cx: &CrateContext,
                                  node_id: ast::NodeId,
                                  global: ValueRef) {
    if cx.dbg_cx().is_none() {
        return;
    }

    // Don't create debuginfo for globals inlined from other crates. The other
    // crate should already contain debuginfo for it. More importantly, the
    // global might not even exist in un-inlined form anywhere which would lead
    // to a linker errors.
    if cx.external_srcs().borrow().contains_key(&node_id) {
        return;
    }

    let var_item = cx.tcx().map.get(node_id);

    let (ident, span) = match var_item {
        ast_map::NodeItem(item) => {
            match item.node {
                ast::ItemStatic(..) => (item.ident, item.span),
                ast::ItemConst(..) => (item.ident, item.span),
                _ => {
                    cx.sess()
                      .span_bug(item.span,
                                &format!("debuginfo::\
                                         create_global_var_metadata() -
                                         Captured var-id refers to \
                                         unexpected ast_item variant: {:?}",
                                        var_item))
                }
            }
        },
        _ => cx.sess().bug(&format!("debuginfo::create_global_var_metadata() \
                                    - Captured var-id refers to unexpected \
                                    ast_map variant: {:?}",
                                   var_item))
    };

    let (file_metadata, line_number) = if span != codemap::DUMMY_SP {
        let loc = span_start(cx, span);
        (file_metadata(cx, &loc.file.name), loc.line as c_uint)
    } else {
        (UNKNOWN_FILE_METADATA, UNKNOWN_LINE_NUMBER)
    };

    let is_local_to_unit = is_node_local_to_unit(cx, node_id);
    let variable_type = ty::node_id_to_type(cx.tcx(), node_id);
    let type_metadata = type_metadata(cx, variable_type, span);
    let namespace_node = namespace_for_item(cx, ast_util::local_def(node_id));
    let var_name = token::get_ident(ident).to_string();
    let linkage_name =
        namespace_node.mangled_name_of_contained_item(&var_name[..]);
    let var_scope = namespace_node.scope;

    let var_name = CString::new(var_name).unwrap();
    let linkage_name = CString::new(linkage_name).unwrap();
    unsafe {
        llvm::LLVMDIBuilderCreateStaticVariable(DIB(cx),
                                                var_scope,
                                                var_name.as_ptr(),
                                                linkage_name.as_ptr(),
                                                file_metadata,
                                                line_number,
                                                type_metadata,
                                                is_local_to_unit,
                                                global,
                                                ptr::null_mut());
    }
}

/// Creates debug information for the given local variable.
///
/// This function assumes that there's a datum for each pattern component of the
/// local in `bcx.fcx.lllocals`.
/// Adds the created metadata nodes directly to the crate's IR.
pub fn create_local_var_metadata(bcx: Block, local: &ast::Local) {
    if bcx.unreachable.get() ||
       fn_should_be_ignored(bcx.fcx) ||
       bcx.sess().opts.debuginfo != FullDebugInfo  {
        return;
    }

    let cx = bcx.ccx();
    let def_map = &cx.tcx().def_map;
    let locals = bcx.fcx.lllocals.borrow();

    pat_util::pat_bindings(def_map, &*local.pat, |_, node_id, span, var_ident| {
        let datum = match locals.get(&node_id) {
            Some(datum) => datum,
            None => {
                bcx.sess().span_bug(span,
                    &format!("no entry in lllocals table for {}",
                            node_id));
            }
        };

        if unsafe { llvm::LLVMIsAAllocaInst(datum.val) } == ptr::null_mut() {
            cx.sess().span_bug(span, "debuginfo::create_local_var_metadata() - \
                                      Referenced variable location is not an alloca!");
        }

        let scope_metadata = scope_metadata(bcx.fcx, node_id, span);

        declare_local(bcx,
                      var_ident.node,
                      datum.ty,
                      scope_metadata,
                      DirectVariable { alloca: datum.val },
                      LocalVariable,
                      span);
    })
}

/// Creates debug information for a variable captured in a closure.
///
/// Adds the created metadata nodes directly to the crate's IR.
pub fn create_captured_var_metadata<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
                                                node_id: ast::NodeId,
                                                env_pointer: ValueRef,
                                                env_index: usize,
                                                captured_by_ref: bool,
                                                span: Span) {
    if bcx.unreachable.get() ||
       fn_should_be_ignored(bcx.fcx) ||
       bcx.sess().opts.debuginfo != FullDebugInfo {
        return;
    }

    let cx = bcx.ccx();

    let ast_item = cx.tcx().map.find(node_id);

    let variable_ident = match ast_item {
        None => {
            cx.sess().span_bug(span, "debuginfo::create_captured_var_metadata: node not found");
        }
        Some(ast_map::NodeLocal(pat)) | Some(ast_map::NodeArg(pat)) => {
            match pat.node {
                ast::PatIdent(_, ref path1, _) => {
                    path1.node
                }
                _ => {
                    cx.sess()
                      .span_bug(span,
                                &format!(
                                "debuginfo::create_captured_var_metadata() - \
                                 Captured var-id refers to unexpected \
                                 ast_map variant: {:?}",
                                 ast_item));
                }
            }
        }
        _ => {
            cx.sess()
              .span_bug(span,
                        &format!("debuginfo::create_captured_var_metadata() - \
                                 Captured var-id refers to unexpected \
                                 ast_map variant: {:?}",
                                ast_item));
        }
    };

    let variable_type = common::node_id_type(bcx, node_id);
    let scope_metadata = bcx.fcx.debug_context.get_ref(cx, span).fn_metadata;

    // env_pointer is the alloca containing the pointer to the environment,
    // so it's type is **EnvironmentType. In order to find out the type of
    // the environment we have to "dereference" two times.
    let llvm_env_data_type = common::val_ty(env_pointer).element_type()
                                                        .element_type();
    let byte_offset_of_var_in_env = machine::llelement_offset(cx,
                                                              llvm_env_data_type,
                                                              env_index);

    let address_operations = unsafe {
        [llvm::LLVMDIBuilderCreateOpDeref(),
         llvm::LLVMDIBuilderCreateOpPlus(),
         byte_offset_of_var_in_env as i64,
         llvm::LLVMDIBuilderCreateOpDeref()]
    };

    let address_op_count = if captured_by_ref {
        address_operations.len()
    } else {
        address_operations.len() - 1
    };

    let variable_access = IndirectVariable {
        alloca: env_pointer,
        address_operations: &address_operations[..address_op_count]
    };

    declare_local(bcx,
                  variable_ident,
                  variable_type,
                  scope_metadata,
                  variable_access,
                  CapturedVariable,
                  span);
}

/// Creates debug information for a local variable introduced in the head of a
/// match-statement arm.
///
/// Adds the created metadata nodes directly to the crate's IR.
pub fn create_match_binding_metadata<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
                                                 variable_ident: ast::Ident,
                                                 binding: BindingInfo<'tcx>) {
    if bcx.unreachable.get() ||
       fn_should_be_ignored(bcx.fcx) ||
       bcx.sess().opts.debuginfo != FullDebugInfo {
        return;
    }

    let scope_metadata = scope_metadata(bcx.fcx, binding.id, binding.span);
    let aops = unsafe {
        [llvm::LLVMDIBuilderCreateOpDeref()]
    };
    // Regardless of the actual type (`T`) we're always passed the stack slot (alloca)
    // for the binding. For ByRef bindings that's a `T*` but for ByMove bindings we
    // actually have `T**`. So to get the actual variable we need to dereference once
    // more. For ByCopy we just use the stack slot we created for the binding.
    let var_access = match binding.trmode {
        TrByCopy(llbinding) => DirectVariable {
            alloca: llbinding
        },
        TrByMove => IndirectVariable {
            alloca: binding.llmatch,
            address_operations: &aops
        },
        TrByRef => DirectVariable {
            alloca: binding.llmatch
        }
    };

    declare_local(bcx,
                  variable_ident,
                  binding.ty,
                  scope_metadata,
                  var_access,
                  LocalVariable,
                  binding.span);
}

/// Creates debug information for the given function argument.
///
/// This function assumes that there's a datum for each pattern component of the
/// argument in `bcx.fcx.lllocals`.
/// Adds the created metadata nodes directly to the crate's IR.
pub fn create_argument_metadata(bcx: Block, arg: &ast::Arg) {
    if bcx.unreachable.get() ||
       fn_should_be_ignored(bcx.fcx) ||
       bcx.sess().opts.debuginfo != FullDebugInfo {
        return;
    }

    let def_map = &bcx.tcx().def_map;
    let scope_metadata = bcx
                         .fcx
                         .debug_context
                         .get_ref(bcx.ccx(), arg.pat.span)
                         .fn_metadata;
    let locals = bcx.fcx.lllocals.borrow();

    pat_util::pat_bindings(def_map, &*arg.pat, |_, node_id, span, var_ident| {
        let datum = match locals.get(&node_id) {
            Some(v) => v,
            None => {
                bcx.sess().span_bug(span,
                    &format!("no entry in lllocals table for {}",
                            node_id));
            }
        };

        if unsafe { llvm::LLVMIsAAllocaInst(datum.val) } == ptr::null_mut() {
            bcx.sess().span_bug(span, "debuginfo::create_argument_metadata() - \
                                       Referenced variable location is not an alloca!");
        }

        let argument_index = {
            let counter = &bcx
                          .fcx
                          .debug_context
                          .get_ref(bcx.ccx(), span)
                          .argument_counter;
            let argument_index = counter.get();
            counter.set(argument_index + 1);
            argument_index
        };

        declare_local(bcx,
                      var_ident.node,
                      datum.ty,
                      scope_metadata,
                      DirectVariable { alloca: datum.val },
                      ArgumentVariable(argument_index),
                      span);
    })
}

pub fn get_cleanup_debug_loc_for_ast_node<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                                                    node_id: ast::NodeId,
                                                    node_span: Span,
                                                    is_block: bool)
                                                 -> NodeIdAndSpan {
    // A debug location needs two things:
    // (1) A span (of which only the beginning will actually be used)
    // (2) An AST node-id which will be used to look up the lexical scope
    //     for the location in the functions scope-map
    //
    // This function will calculate the debug location for compiler-generated
    // cleanup calls that are executed when control-flow leaves the
    // scope identified by `node_id`.
    //
    // For everything but block-like things we can simply take id and span of
    // the given expression, meaning that from a debugger's view cleanup code is
    // executed at the same source location as the statement/expr itself.
    //
    // Blocks are a special case. Here we want the cleanup to be linked to the
    // closing curly brace of the block. The *scope* the cleanup is executed in
    // is up to debate: It could either still be *within* the block being
    // cleaned up, meaning that locals from the block are still visible in the
    // debugger.
    // Or it could be in the scope that the block is contained in, so any locals
    // from within the block are already considered out-of-scope and thus not
    // accessible in the debugger anymore.
    //
    // The current implementation opts for the second option: cleanup of a block
    // already happens in the parent scope of the block. The main reason for
    // this decision is that scoping becomes controlflow dependent when variable
    // shadowing is involved and it's impossible to decide statically which
    // scope is actually left when the cleanup code is executed.
    // In practice it shouldn't make much of a difference.

    let mut cleanup_span = node_span;

    if is_block {
        // Not all blocks actually have curly braces (e.g. simple closure
        // bodies), in which case we also just want to return the span of the
        // whole expression.
        let code_snippet = cx.sess().codemap().span_to_snippet(node_span);
        if let Ok(code_snippet) = code_snippet {
            let bytes = code_snippet.as_bytes();

            if bytes.len() > 0 && &bytes[bytes.len()-1..] == b"}" {
                cleanup_span = Span {
                    lo: node_span.hi - codemap::BytePos(1),
                    hi: node_span.hi,
                    expn_id: node_span.expn_id
                };
            }
        }
    }

    NodeIdAndSpan {
        id: node_id,
        span: cleanup_span
    }
}

#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub enum DebugLoc {
    At(ast::NodeId, Span),
    None
}

impl DebugLoc {
    pub fn apply(&self, fcx: &FunctionContext) {
        match *self {
            DebugLoc::At(node_id, span) => {
                set_source_location(fcx, node_id, span);
            }
            DebugLoc::None => {
                clear_source_location(fcx);
            }
        }
    }
}

pub trait ToDebugLoc {
    fn debug_loc(&self) -> DebugLoc;
}

impl ToDebugLoc for ast::Expr {
    fn debug_loc(&self) -> DebugLoc {
        DebugLoc::At(self.id, self.span)
    }
}

impl ToDebugLoc for NodeIdAndSpan {
    fn debug_loc(&self) -> DebugLoc {
        DebugLoc::At(self.id, self.span)
    }
}

impl ToDebugLoc for Option<NodeIdAndSpan> {
    fn debug_loc(&self) -> DebugLoc {
        match *self {
            Some(NodeIdAndSpan { id, span }) => DebugLoc::At(id, span),
            None => DebugLoc::None
        }
    }
}

/// Sets the current debug location at the beginning of the span.
///
/// Maps to a call to llvm::LLVMSetCurrentDebugLocation(...). The node_id
/// parameter is used to reliably find the correct visibility scope for the code
/// position.
pub fn set_source_location(fcx: &FunctionContext,
                           node_id: ast::NodeId,
                           span: Span) {
    match fcx.debug_context {
        FunctionDebugContext::DebugInfoDisabled => return,
        FunctionDebugContext::FunctionWithoutDebugInfo => {
            set_debug_location(fcx.ccx, UnknownLocation);
            return;
        }
        FunctionDebugContext::RegularContext(box ref function_debug_context) => {
            if function_debug_context.source_location_override.get() {
                // Just ignore any attempts to set a new debug location while
                // the override is active.
                return;
            }

            let cx = fcx.ccx;

            debug!("set_source_location: {}", cx.sess().codemap().span_to_string(span));

            if function_debug_context.source_locations_enabled.get() {
                let loc = span_start(cx, span);
                let scope = scope_metadata(fcx, node_id, span);

                set_debug_location(cx, InternalDebugLocation::new(scope,
                                                                  loc.line,
                                                                  loc.col.to_usize()));
            } else {
                set_debug_location(cx, UnknownLocation);
            }
        }
    }
}

/// This function makes sure that all debug locations emitted while executing
/// `wrapped_function` are set to the given `debug_loc`.
pub fn with_source_location_override<F, R>(fcx: &FunctionContext,
                                           debug_loc: DebugLoc,
                                           wrapped_function: F) -> R
    where F: FnOnce() -> R
{
    match fcx.debug_context {
        FunctionDebugContext::DebugInfoDisabled => {
            wrapped_function()
        }
        FunctionDebugContext::FunctionWithoutDebugInfo => {
            set_debug_location(fcx.ccx, UnknownLocation);
            wrapped_function()
        }
        FunctionDebugContext::RegularContext(box ref function_debug_context) => {
            if function_debug_context.source_location_override.get() {
                wrapped_function()
            } else {
                debug_loc.apply(fcx);
                function_debug_context.source_location_override.set(true);
                let result = wrapped_function();
                function_debug_context.source_location_override.set(false);
                result
            }
        }
    }
}

/// Clears the current debug location.
///
/// Instructions generated hereafter won't be assigned a source location.
pub fn clear_source_location(fcx: &FunctionContext) {
    if fn_should_be_ignored(fcx) {
        return;
    }

    set_debug_location(fcx.ccx, UnknownLocation);
}

/// Enables emitting source locations for the given functions.
///
/// Since we don't want source locations to be emitted for the function prelude,
/// they are disabled when beginning to translate a new function. This functions
/// switches source location emitting on and must therefore be called before the
/// first real statement/expression of the function is translated.
pub fn start_emitting_source_locations(fcx: &FunctionContext) {
    match fcx.debug_context {
        FunctionDebugContext::RegularContext(box ref data) => {
            data.source_locations_enabled.set(true)
        },
        _ => { /* safe to ignore */ }
    }
}

/// Creates the function-specific debug context.
///
/// Returns the FunctionDebugContext for the function which holds state needed
/// for debug info creation. The function may also return another variant of the
/// FunctionDebugContext enum which indicates why no debuginfo should be created
/// for the function.
pub fn create_function_debug_context<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                                               fn_ast_id: ast::NodeId,
                                               param_substs: &Substs<'tcx>,
                                               llfn: ValueRef) -> FunctionDebugContext {
    if cx.sess().opts.debuginfo == NoDebugInfo {
        return FunctionDebugContext::DebugInfoDisabled;
    }

    // Clear the debug location so we don't assign them in the function prelude.
    // Do this here already, in case we do an early exit from this function.
    set_debug_location(cx, UnknownLocation);

    if fn_ast_id == ast::DUMMY_NODE_ID {
        // This is a function not linked to any source location, so don't
        // generate debuginfo for it.
        return FunctionDebugContext::FunctionWithoutDebugInfo;
    }

    let empty_generics = ast_util::empty_generics();

    let fnitem = cx.tcx().map.get(fn_ast_id);

    let (ident, fn_decl, generics, top_level_block, span, has_path) = match fnitem {
        ast_map::NodeItem(ref item) => {
            if contains_nodebug_attribute(&item.attrs) {
                return FunctionDebugContext::FunctionWithoutDebugInfo;
            }

            match item.node {
                ast::ItemFn(ref fn_decl, _, _, ref generics, ref top_level_block) => {
                    (item.ident, fn_decl, generics, top_level_block, item.span, true)
                }
                _ => {
                    cx.sess().span_bug(item.span,
                        "create_function_debug_context: item bound to non-function");
                }
            }
        }
        ast_map::NodeImplItem(impl_item) => {
            match impl_item.node {
                ast::MethodImplItem(ref sig, ref body) => {
                    if contains_nodebug_attribute(&impl_item.attrs) {
                        return FunctionDebugContext::FunctionWithoutDebugInfo;
                    }

                    (impl_item.ident,
                     &sig.decl,
                     &sig.generics,
                     body,
                     impl_item.span,
                     true)
                }
                ast::TypeImplItem(_) => {
                    cx.sess().span_bug(impl_item.span,
                                       "create_function_debug_context() \
                                        called on associated type?!")
                }
                ast::MacImplItem(_) => {
                    cx.sess().span_bug(impl_item.span,
                                       "create_function_debug_context() \
                                        called on unexpanded macro?!")
                }
            }
        }
        ast_map::NodeExpr(ref expr) => {
            match expr.node {
                ast::ExprClosure(_, ref fn_decl, ref top_level_block) => {
                    let name = format!("fn{}", token::gensym("fn"));
                    let name = token::str_to_ident(&name[..]);
                    (name, fn_decl,
                        // This is not quite right. It should actually inherit
                        // the generics of the enclosing function.
                        &empty_generics,
                        top_level_block,
                        expr.span,
                        // Don't try to lookup the item path:
                        false)
                }
                _ => cx.sess().span_bug(expr.span,
                        "create_function_debug_context: expected an expr_fn_block here")
            }
        }
        ast_map::NodeTraitItem(trait_item) => {
            match trait_item.node {
                ast::MethodTraitItem(ref sig, Some(ref body)) => {
                    if contains_nodebug_attribute(&trait_item.attrs) {
                        return FunctionDebugContext::FunctionWithoutDebugInfo;
                    }

                    (trait_item.ident,
                     &sig.decl,
                     &sig.generics,
                     body,
                     trait_item.span,
                     true)
                }
                _ => {
                    cx.sess()
                      .bug(&format!("create_function_debug_context: \
                                    unexpected sort of node: {:?}",
                                    fnitem))
                }
            }
        }
        ast_map::NodeForeignItem(..) |
        ast_map::NodeVariant(..) |
        ast_map::NodeStructCtor(..) => {
            return FunctionDebugContext::FunctionWithoutDebugInfo;
        }
        _ => cx.sess().bug(&format!("create_function_debug_context: \
                                    unexpected sort of node: {:?}",
                                   fnitem))
    };

    // This can be the case for functions inlined from another crate
    if span == codemap::DUMMY_SP {
        return FunctionDebugContext::FunctionWithoutDebugInfo;
    }

    let loc = span_start(cx, span);
    let file_metadata = file_metadata(cx, &loc.file.name);

    let function_type_metadata = unsafe {
        let fn_signature = get_function_signature(cx,
                                                  fn_ast_id,
                                                  &*fn_decl,
                                                  param_substs,
                                                  span);
        llvm::LLVMDIBuilderCreateSubroutineType(DIB(cx), file_metadata, fn_signature)
    };

    // Get_template_parameters() will append a `<...>` clause to the function
    // name if necessary.
    let mut function_name = String::from_str(&token::get_ident(ident));
    let template_parameters = get_template_parameters(cx,
                                                      generics,
                                                      param_substs,
                                                      file_metadata,
                                                      &mut function_name);

    // There is no ast_map::Path for ast::ExprClosure-type functions. For now,
    // just don't put them into a namespace. In the future this could be improved
    // somehow (storing a path in the ast_map, or construct a path using the
    // enclosing function).
    let (linkage_name, containing_scope) = if has_path {
        let namespace_node = namespace_for_item(cx, ast_util::local_def(fn_ast_id));
        let linkage_name = namespace_node.mangled_name_of_contained_item(
            &function_name[..]);
        let containing_scope = namespace_node.scope;
        (linkage_name, containing_scope)
    } else {
        (function_name.clone(), file_metadata)
    };

    // Clang sets this parameter to the opening brace of the function's block,
    // so let's do this too.
    let scope_line = span_start(cx, top_level_block.span).line;

    let is_local_to_unit = is_node_local_to_unit(cx, fn_ast_id);

    let function_name = CString::new(function_name).unwrap();
    let linkage_name = CString::new(linkage_name).unwrap();
    let fn_metadata = unsafe {
        llvm::LLVMDIBuilderCreateFunction(
            DIB(cx),
            containing_scope,
            function_name.as_ptr(),
            linkage_name.as_ptr(),
            file_metadata,
            loc.line as c_uint,
            function_type_metadata,
            is_local_to_unit,
            true,
            scope_line as c_uint,
            FlagPrototyped as c_uint,
            cx.sess().opts.optimize != config::No,
            llfn,
            template_parameters,
            ptr::null_mut())
    };

    let scope_map = create_scope_map(cx,
                                     &fn_decl.inputs,
                                     &*top_level_block,
                                     fn_metadata,
                                     fn_ast_id);

    // Initialize fn debug context (including scope map and namespace map)
    let fn_debug_context = box FunctionDebugContextData {
        scope_map: RefCell::new(scope_map),
        fn_metadata: fn_metadata,
        argument_counter: Cell::new(1),
        source_locations_enabled: Cell::new(false),
        source_location_override: Cell::new(false),
    };



    return FunctionDebugContext::RegularContext(fn_debug_context);

    fn get_function_signature<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                                        fn_ast_id: ast::NodeId,
                                        fn_decl: &ast::FnDecl,
                                        param_substs: &Substs<'tcx>,
                                        error_reporting_span: Span) -> DIArray {
        if cx.sess().opts.debuginfo == LimitedDebugInfo {
            return create_DIArray(DIB(cx), &[]);
        }

        let mut signature = Vec::with_capacity(fn_decl.inputs.len() + 1);

        // Return type -- llvm::DIBuilder wants this at index 0
        assert_type_for_node_id(cx, fn_ast_id, error_reporting_span);
        let return_type = ty::node_id_to_type(cx.tcx(), fn_ast_id);
        let return_type = monomorphize::apply_param_substs(cx.tcx(),
                                                           param_substs,
                                                           &return_type);
        if ty::type_is_nil(return_type) {
            signature.push(ptr::null_mut())
        } else {
            signature.push(type_metadata(cx, return_type, codemap::DUMMY_SP));
        }

        // Arguments types
        for arg in &fn_decl.inputs {
            assert_type_for_node_id(cx, arg.pat.id, arg.pat.span);
            let arg_type = ty::node_id_to_type(cx.tcx(), arg.pat.id);
            let arg_type = monomorphize::apply_param_substs(cx.tcx(),
                                                            param_substs,
                                                            &arg_type);
            signature.push(type_metadata(cx, arg_type, codemap::DUMMY_SP));
        }

        return create_DIArray(DIB(cx), &signature[..]);
    }

    fn get_template_parameters<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                                         generics: &ast::Generics,
                                         param_substs: &Substs<'tcx>,
                                         file_metadata: DIFile,
                                         name_to_append_suffix_to: &mut String)
                                         -> DIArray
    {
        let self_type = param_substs.self_ty();
        let self_type = monomorphize::normalize_associated_type(cx.tcx(), &self_type);

        // Only true for static default methods:
        let has_self_type = self_type.is_some();

        if !generics.is_type_parameterized() && !has_self_type {
            return create_DIArray(DIB(cx), &[]);
        }

        name_to_append_suffix_to.push('<');

        // The list to be filled with template parameters:
        let mut template_params: Vec<DIDescriptor> =
            Vec::with_capacity(generics.ty_params.len() + 1);

        // Handle self type
        if has_self_type {
            let actual_self_type = self_type.unwrap();
            // Add self type name to <...> clause of function name
            let actual_self_type_name = compute_debuginfo_type_name(
                cx,
                actual_self_type,
                true);

            name_to_append_suffix_to.push_str(&actual_self_type_name[..]);

            if generics.is_type_parameterized() {
                name_to_append_suffix_to.push_str(",");
            }

            // Only create type information if full debuginfo is enabled
            if cx.sess().opts.debuginfo == FullDebugInfo {
                let actual_self_type_metadata = type_metadata(cx,
                                                              actual_self_type,
                                                              codemap::DUMMY_SP);

                let ident = special_idents::type_self;

                let ident = token::get_ident(ident);
                let name = CString::new(ident.as_bytes()).unwrap();
                let param_metadata = unsafe {
                    llvm::LLVMDIBuilderCreateTemplateTypeParameter(
                        DIB(cx),
                        file_metadata,
                        name.as_ptr(),
                        actual_self_type_metadata,
                        ptr::null_mut(),
                        0,
                        0)
                };

                template_params.push(param_metadata);
            }
        }

        // Handle other generic parameters
        let actual_types = param_substs.types.get_slice(subst::FnSpace);
        for (index, &ast::TyParam{ ident, .. }) in generics.ty_params.iter().enumerate() {
            let actual_type = actual_types[index];
            // Add actual type name to <...> clause of function name
            let actual_type_name = compute_debuginfo_type_name(cx,
                                                               actual_type,
                                                               true);
            name_to_append_suffix_to.push_str(&actual_type_name[..]);

            if index != generics.ty_params.len() - 1 {
                name_to_append_suffix_to.push_str(",");
            }

            // Again, only create type information if full debuginfo is enabled
            if cx.sess().opts.debuginfo == FullDebugInfo {
                let actual_type_metadata = type_metadata(cx, actual_type, codemap::DUMMY_SP);
                let ident = token::get_ident(ident);
                let name = CString::new(ident.as_bytes()).unwrap();
                let param_metadata = unsafe {
                    llvm::LLVMDIBuilderCreateTemplateTypeParameter(
                        DIB(cx),
                        file_metadata,
                        name.as_ptr(),
                        actual_type_metadata,
                        ptr::null_mut(),
                        0,
                        0)
                };
                template_params.push(param_metadata);
            }
        }

        name_to_append_suffix_to.push('>');

        return create_DIArray(DIB(cx), &template_params[..]);
    }
}

//=-----------------------------------------------------------------------------
// Module-Internal debug info creation functions
//=-----------------------------------------------------------------------------

fn is_node_local_to_unit(cx: &CrateContext, node_id: ast::NodeId) -> bool
{
    // The is_local_to_unit flag indicates whether a function is local to the
    // current compilation unit (i.e. if it is *static* in the C-sense). The
    // *reachable* set should provide a good approximation of this, as it
    // contains everything that might leak out of the current crate (by being
    // externally visible or by being inlined into something externally visible).
    // It might better to use the `exported_items` set from `driver::CrateAnalysis`
    // in the future, but (atm) this set is not available in the translation pass.
    !cx.reachable().contains(&node_id)
}

#[allow(non_snake_case)]
fn create_DIArray(builder: DIBuilderRef, arr: &[DIDescriptor]) -> DIArray {
    return unsafe {
        llvm::LLVMDIBuilderGetOrCreateArray(builder, arr.as_ptr(), arr.len() as u32)
    };
}

fn compile_unit_metadata(cx: &CrateContext) -> DIDescriptor {
    let work_dir = &cx.sess().working_dir;
    let compile_unit_name = match cx.sess().local_crate_source_file {
        None => fallback_path(cx),
        Some(ref abs_path) => {
            if abs_path.is_relative() {
                cx.sess().warn("debuginfo: Invalid path to crate's local root source file!");
                fallback_path(cx)
            } else {
                match abs_path.relative_from(work_dir) {
                    Some(ref p) if p.is_relative() => {
                        if p.starts_with(Path::new("./")) {
                            path2cstr(p)
                        } else {
                            path2cstr(&Path::new(".").join(p))
                        }
                    }
                    _ => fallback_path(cx)
                }
            }
        }
    };

    debug!("compile_unit_metadata: {:?}", compile_unit_name);
    let producer = format!("rustc version {}",
                           (option_env!("CFG_VERSION")).expect("CFG_VERSION"));

    let compile_unit_name = compile_unit_name.as_ptr();
    let work_dir = path2cstr(&work_dir);
    let producer = CString::new(producer).unwrap();
    let flags = "\0";
    let split_name = "\0";
    return unsafe {
        llvm::LLVMDIBuilderCreateCompileUnit(
            debug_context(cx).builder,
            DW_LANG_RUST,
            compile_unit_name,
            work_dir.as_ptr(),
            producer.as_ptr(),
            cx.sess().opts.optimize != config::No,
            flags.as_ptr() as *const _,
            0,
            split_name.as_ptr() as *const _)
    };

    fn fallback_path(cx: &CrateContext) -> CString {
        CString::new(cx.link_meta().crate_name.clone()).unwrap()
    }
}

fn declare_local<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
                             variable_ident: ast::Ident,
                             variable_type: Ty<'tcx>,
                             scope_metadata: DIScope,
                             variable_access: VariableAccess,
                             variable_kind: VariableKind,
                             span: Span) {
    let cx: &CrateContext = bcx.ccx();

    let filename = span_start(cx, span).file.name.clone();
    let file_metadata = file_metadata(cx, &filename[..]);

    let name = token::get_ident(variable_ident);
    let loc = span_start(cx, span);
    let type_metadata = type_metadata(cx, variable_type, span);

    let (argument_index, dwarf_tag) = match variable_kind {
        ArgumentVariable(index) => (index as c_uint, DW_TAG_arg_variable),
        LocalVariable    |
        CapturedVariable => (0, DW_TAG_auto_variable)
    };

    let name = CString::new(name.as_bytes()).unwrap();
    match (variable_access, &[][..]) {
        (DirectVariable { alloca }, address_operations) |
        (IndirectVariable {alloca, address_operations}, _) => {
            let metadata = unsafe {
                llvm::LLVMDIBuilderCreateVariable(
                    DIB(cx),
                    dwarf_tag,
                    scope_metadata,
                    name.as_ptr(),
                    file_metadata,
                    loc.line as c_uint,
                    type_metadata,
                    cx.sess().opts.optimize != config::No,
                    0,
                    address_operations.as_ptr(),
                    address_operations.len() as c_uint,
                    argument_index)
            };
            set_debug_location(cx, InternalDebugLocation::new(scope_metadata,
                                                      loc.line,
                                                      loc.col.to_usize()));
            unsafe {
                let instr = llvm::LLVMDIBuilderInsertDeclareAtEnd(
                    DIB(cx),
                    alloca,
                    metadata,
                    address_operations.as_ptr(),
                    address_operations.len() as c_uint,
                    bcx.llbb);

                llvm::LLVMSetInstDebugLocation(trans::build::B(bcx).llbuilder, instr);
            }
        }
    }

    match variable_kind {
        ArgumentVariable(_) | CapturedVariable => {
            assert!(!bcx.fcx
                        .debug_context
                        .get_ref(cx, span)
                        .source_locations_enabled
                        .get());
            set_debug_location(cx, UnknownLocation);
        }
        _ => { /* nothing to do */ }
    }
}

fn file_metadata(cx: &CrateContext, full_path: &str) -> DIFile {
    match debug_context(cx).created_files.borrow().get(full_path) {
        Some(file_metadata) => return *file_metadata,
        None => ()
    }

    debug!("file_metadata: {}", full_path);

    // FIXME (#9639): This needs to handle non-utf8 paths
    let work_dir = cx.sess().working_dir.to_str().unwrap();
    let file_name =
        if full_path.starts_with(work_dir) {
            &full_path[work_dir.len() + 1..full_path.len()]
        } else {
            full_path
        };

    let file_name = CString::new(file_name).unwrap();
    let work_dir = CString::new(work_dir).unwrap();
    let file_metadata = unsafe {
        llvm::LLVMDIBuilderCreateFile(DIB(cx), file_name.as_ptr(),
                                      work_dir.as_ptr())
    };

    let mut created_files = debug_context(cx).created_files.borrow_mut();
    created_files.insert(full_path.to_string(), file_metadata);
    return file_metadata;
}

/// Finds the scope metadata node for the given AST node.
fn scope_metadata(fcx: &FunctionContext,
                  node_id: ast::NodeId,
                  error_reporting_span: Span)
               -> DIScope {
    let scope_map = &fcx.debug_context
                        .get_ref(fcx.ccx, error_reporting_span)
                        .scope_map;
    match scope_map.borrow().get(&node_id).cloned() {
        Some(scope_metadata) => scope_metadata,
        None => {
            let node = fcx.ccx.tcx().map.get(node_id);

            fcx.ccx.sess().span_bug(error_reporting_span,
                &format!("debuginfo: Could not find scope info for node {:?}",
                        node));
        }
    }
}

fn diverging_type_metadata(cx: &CrateContext) -> DIType {
    unsafe {
        llvm::LLVMDIBuilderCreateBasicType(
            DIB(cx),
            "!\0".as_ptr() as *const _,
            bytes_to_bits(0),
            bytes_to_bits(0),
            DW_ATE_unsigned)
    }
}

fn basic_type_metadata<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                                 t: Ty<'tcx>) -> DIType {

    debug!("basic_type_metadata: {:?}", t);

    let (name, encoding) = match t.sty {
        ty::ty_tup(ref elements) if elements.is_empty() =>
            ("()".to_string(), DW_ATE_unsigned),
        ty::ty_bool => ("bool".to_string(), DW_ATE_boolean),
        ty::ty_char => ("char".to_string(), DW_ATE_unsigned_char),
        ty::ty_int(int_ty) => match int_ty {
            ast::TyIs => ("isize".to_string(), DW_ATE_signed),
            ast::TyI8 => ("i8".to_string(), DW_ATE_signed),
            ast::TyI16 => ("i16".to_string(), DW_ATE_signed),
            ast::TyI32 => ("i32".to_string(), DW_ATE_signed),
            ast::TyI64 => ("i64".to_string(), DW_ATE_signed)
        },
        ty::ty_uint(uint_ty) => match uint_ty {
            ast::TyUs => ("usize".to_string(), DW_ATE_unsigned),
            ast::TyU8 => ("u8".to_string(), DW_ATE_unsigned),
            ast::TyU16 => ("u16".to_string(), DW_ATE_unsigned),
            ast::TyU32 => ("u32".to_string(), DW_ATE_unsigned),
            ast::TyU64 => ("u64".to_string(), DW_ATE_unsigned)
        },
        ty::ty_float(float_ty) => match float_ty {
            ast::TyF32 => ("f32".to_string(), DW_ATE_float),
            ast::TyF64 => ("f64".to_string(), DW_ATE_float),
        },
        _ => cx.sess().bug("debuginfo::basic_type_metadata - t is invalid type")
    };

    let llvm_type = type_of::type_of(cx, t);
    let (size, align) = size_and_align_of(cx, llvm_type);
    let name = CString::new(name).unwrap();
    let ty_metadata = unsafe {
        llvm::LLVMDIBuilderCreateBasicType(
            DIB(cx),
            name.as_ptr(),
            bytes_to_bits(size),
            bytes_to_bits(align),
            encoding)
    };

    return ty_metadata;
}

fn pointer_type_metadata<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                                   pointer_type: Ty<'tcx>,
                                   pointee_type_metadata: DIType)
                                   -> DIType {
    let pointer_llvm_type = type_of::type_of(cx, pointer_type);
    let (pointer_size, pointer_align) = size_and_align_of(cx, pointer_llvm_type);
    let name = compute_debuginfo_type_name(cx, pointer_type, false);
    let name = CString::new(name).unwrap();
    let ptr_metadata = unsafe {
        llvm::LLVMDIBuilderCreatePointerType(
            DIB(cx),
            pointee_type_metadata,
            bytes_to_bits(pointer_size),
            bytes_to_bits(pointer_align),
            name.as_ptr())
    };
    return ptr_metadata;
}

//=-----------------------------------------------------------------------------
// Common facilities for record-like types (structs, enums, tuples)
//=-----------------------------------------------------------------------------

enum MemberOffset {
    FixedMemberOffset { bytes: usize },
    // For ComputedMemberOffset, the offset is read from the llvm type definition
    ComputedMemberOffset
}

// Description of a type member, which can either be a regular field (as in
// structs or tuples) or an enum variant
struct MemberDescription {
    name: String,
    llvm_type: Type,
    type_metadata: DIType,
    offset: MemberOffset,
    flags: c_uint
}

// A factory for MemberDescriptions. It produces a list of member descriptions
// for some record-like type. MemberDescriptionFactories are used to defer the
// creation of type member descriptions in order to break cycles arising from
// recursive type definitions.
enum MemberDescriptionFactory<'tcx> {
    StructMDF(StructMemberDescriptionFactory<'tcx>),
    TupleMDF(TupleMemberDescriptionFactory<'tcx>),
    EnumMDF(EnumMemberDescriptionFactory<'tcx>),
    VariantMDF(VariantMemberDescriptionFactory<'tcx>)
}

impl<'tcx> MemberDescriptionFactory<'tcx> {
    fn create_member_descriptions<'a>(&self, cx: &CrateContext<'a, 'tcx>)
                                      -> Vec<MemberDescription> {
        match *self {
            StructMDF(ref this) => {
                this.create_member_descriptions(cx)
            }
            TupleMDF(ref this) => {
                this.create_member_descriptions(cx)
            }
            EnumMDF(ref this) => {
                this.create_member_descriptions(cx)
            }
            VariantMDF(ref this) => {
                this.create_member_descriptions(cx)
            }
        }
    }
}

// A description of some recursive type. It can either be already finished (as
// with FinalMetadata) or it is not yet finished, but contains all information
// needed to generate the missing parts of the description. See the documentation
// section on Recursive Types at the top of this file for more information.
enum RecursiveTypeDescription<'tcx> {
    UnfinishedMetadata {
        unfinished_type: Ty<'tcx>,
        unique_type_id: UniqueTypeId,
        metadata_stub: DICompositeType,
        llvm_type: Type,
        member_description_factory: MemberDescriptionFactory<'tcx>,
    },
    FinalMetadata(DICompositeType)
}

fn create_and_register_recursive_type_forward_declaration<'a, 'tcx>(
    cx: &CrateContext<'a, 'tcx>,
    unfinished_type: Ty<'tcx>,
    unique_type_id: UniqueTypeId,
    metadata_stub: DICompositeType,
    llvm_type: Type,
    member_description_factory: MemberDescriptionFactory<'tcx>)
 -> RecursiveTypeDescription<'tcx> {

    // Insert the stub into the TypeMap in order to allow for recursive references
    let mut type_map = debug_context(cx).type_map.borrow_mut();
    type_map.register_unique_id_with_metadata(cx, unique_type_id, metadata_stub);
    type_map.register_type_with_metadata(cx, unfinished_type, metadata_stub);

    UnfinishedMetadata {
        unfinished_type: unfinished_type,
        unique_type_id: unique_type_id,
        metadata_stub: metadata_stub,
        llvm_type: llvm_type,
        member_description_factory: member_description_factory,
    }
}

impl<'tcx> RecursiveTypeDescription<'tcx> {
    // Finishes up the description of the type in question (mostly by providing
    // descriptions of the fields of the given type) and returns the final type metadata.
    fn finalize<'a>(&self, cx: &CrateContext<'a, 'tcx>) -> MetadataCreationResult {
        match *self {
            FinalMetadata(metadata) => MetadataCreationResult::new(metadata, false),
            UnfinishedMetadata {
                unfinished_type,
                unique_type_id,
                metadata_stub,
                llvm_type,
                ref member_description_factory,
                ..
            } => {
                // Make sure that we have a forward declaration of the type in
                // the TypeMap so that recursive references are possible. This
                // will always be the case if the RecursiveTypeDescription has
                // been properly created through the
                // create_and_register_recursive_type_forward_declaration() function.
                {
                    let type_map = debug_context(cx).type_map.borrow();
                    if type_map.find_metadata_for_unique_id(unique_type_id).is_none() ||
                       type_map.find_metadata_for_type(unfinished_type).is_none() {
                        cx.sess().bug(&format!("Forward declaration of potentially recursive type \
                                              '{}' was not found in TypeMap!",
                                              ppaux::ty_to_string(cx.tcx(), unfinished_type))
                                      );
                    }
                }

                // ... then create the member descriptions ...
                let member_descriptions =
                    member_description_factory.create_member_descriptions(cx);

                // ... and attach them to the stub to complete it.
                set_members_of_composite_type(cx,
                                              metadata_stub,
                                              llvm_type,
                                              &member_descriptions[..]);
                return MetadataCreationResult::new(metadata_stub, true);
            }
        }
    }
}


//=-----------------------------------------------------------------------------
// Structs
//=-----------------------------------------------------------------------------

// Creates MemberDescriptions for the fields of a struct
struct StructMemberDescriptionFactory<'tcx> {
    fields: Vec<ty::field<'tcx>>,
    is_simd: bool,
    span: Span,
}

impl<'tcx> StructMemberDescriptionFactory<'tcx> {
    fn create_member_descriptions<'a>(&self, cx: &CrateContext<'a, 'tcx>)
                                      -> Vec<MemberDescription> {
        if self.fields.len() == 0 {
            return Vec::new();
        }

        let field_size = if self.is_simd {
            machine::llsize_of_alloc(cx, type_of::type_of(cx, self.fields[0].mt.ty)) as usize
        } else {
            0xdeadbeef
        };

        self.fields.iter().enumerate().map(|(i, field)| {
            let name = if field.name == special_idents::unnamed_field.name {
                "".to_string()
            } else {
                token::get_name(field.name).to_string()
            };

            let offset = if self.is_simd {
                assert!(field_size != 0xdeadbeef);
                FixedMemberOffset { bytes: i * field_size }
            } else {
                ComputedMemberOffset
            };

            MemberDescription {
                name: name,
                llvm_type: type_of::type_of(cx, field.mt.ty),
                type_metadata: type_metadata(cx, field.mt.ty, self.span),
                offset: offset,
                flags: FLAGS_NONE,
            }
        }).collect()
    }
}


fn prepare_struct_metadata<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                                     struct_type: Ty<'tcx>,
                                     def_id: ast::DefId,
                                     substs: &subst::Substs<'tcx>,
                                     unique_type_id: UniqueTypeId,
                                     span: Span)
                                     -> RecursiveTypeDescription<'tcx> {
    let struct_name = compute_debuginfo_type_name(cx, struct_type, false);
    let struct_llvm_type = type_of::type_of(cx, struct_type);

    let (containing_scope, _) = get_namespace_and_span_for_item(cx, def_id);

    let struct_metadata_stub = create_struct_stub(cx,
                                                  struct_llvm_type,
                                                  &struct_name[..],
                                                  unique_type_id,
                                                  containing_scope);

    let mut fields = ty::struct_fields(cx.tcx(), def_id, substs);

    // The `Ty` values returned by `ty::struct_fields` can still contain
    // `ty_projection` variants, so normalize those away.
    for field in &mut fields {
        field.mt.ty = monomorphize::normalize_associated_type(cx.tcx(), &field.mt.ty);
    }

    create_and_register_recursive_type_forward_declaration(
        cx,
        struct_type,
        unique_type_id,
        struct_metadata_stub,
        struct_llvm_type,
        StructMDF(StructMemberDescriptionFactory {
            fields: fields,
            is_simd: ty::type_is_simd(cx.tcx(), struct_type),
            span: span,
        })
    )
}


//=-----------------------------------------------------------------------------
// Tuples
//=-----------------------------------------------------------------------------

// Creates MemberDescriptions for the fields of a tuple
struct TupleMemberDescriptionFactory<'tcx> {
    component_types: Vec<Ty<'tcx>>,
    span: Span,
}

impl<'tcx> TupleMemberDescriptionFactory<'tcx> {
    fn create_member_descriptions<'a>(&self, cx: &CrateContext<'a, 'tcx>)
                                      -> Vec<MemberDescription> {
        self.component_types.iter().map(|&component_type| {
            MemberDescription {
                name: "".to_string(),
                llvm_type: type_of::type_of(cx, component_type),
                type_metadata: type_metadata(cx, component_type, self.span),
                offset: ComputedMemberOffset,
                flags: FLAGS_NONE,
            }
        }).collect()
    }
}

fn prepare_tuple_metadata<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                                    tuple_type: Ty<'tcx>,
                                    component_types: &[Ty<'tcx>],
                                    unique_type_id: UniqueTypeId,
                                    span: Span)
                                    -> RecursiveTypeDescription<'tcx> {
    let tuple_name = compute_debuginfo_type_name(cx, tuple_type, false);
    let tuple_llvm_type = type_of::type_of(cx, tuple_type);

    create_and_register_recursive_type_forward_declaration(
        cx,
        tuple_type,
        unique_type_id,
        create_struct_stub(cx,
                           tuple_llvm_type,
                           &tuple_name[..],
                           unique_type_id,
                           UNKNOWN_SCOPE_METADATA),
        tuple_llvm_type,
        TupleMDF(TupleMemberDescriptionFactory {
            component_types: component_types.to_vec(),
            span: span,
        })
    )
}


//=-----------------------------------------------------------------------------
// Enums
//=-----------------------------------------------------------------------------

// Describes the members of an enum value: An enum is described as a union of
// structs in DWARF. This MemberDescriptionFactory provides the description for
// the members of this union; so for every variant of the given enum, this factory
// will produce one MemberDescription (all with no name and a fixed offset of
// zero bytes).
struct EnumMemberDescriptionFactory<'tcx> {
    enum_type: Ty<'tcx>,
    type_rep: Rc<adt::Repr<'tcx>>,
    variants: Rc<Vec<Rc<ty::VariantInfo<'tcx>>>>,
    discriminant_type_metadata: Option<DIType>,
    containing_scope: DIScope,
    file_metadata: DIFile,
    span: Span,
}

impl<'tcx> EnumMemberDescriptionFactory<'tcx> {
    fn create_member_descriptions<'a>(&self, cx: &CrateContext<'a, 'tcx>)
                                      -> Vec<MemberDescription> {
        match *self.type_rep {
            adt::General(_, ref struct_defs, _) => {
                let discriminant_info = RegularDiscriminant(self.discriminant_type_metadata
                    .expect(""));

                struct_defs
                    .iter()
                    .enumerate()
                    .map(|(i, struct_def)| {
                        let (variant_type_metadata,
                             variant_llvm_type,
                             member_desc_factory) =
                            describe_enum_variant(cx,
                                                  self.enum_type,
                                                  struct_def,
                                                  &*(*self.variants)[i],
                                                  discriminant_info,
                                                  self.containing_scope,
                                                  self.span);

                        let member_descriptions = member_desc_factory
                            .create_member_descriptions(cx);

                        set_members_of_composite_type(cx,
                                                      variant_type_metadata,
                                                      variant_llvm_type,
                                                      &member_descriptions[..]);
                        MemberDescription {
                            name: "".to_string(),
                            llvm_type: variant_llvm_type,
                            type_metadata: variant_type_metadata,
                            offset: FixedMemberOffset { bytes: 0 },
                            flags: FLAGS_NONE
                        }
                    }).collect()
            },
            adt::Univariant(ref struct_def, _) => {
                assert!(self.variants.len() <= 1);

                if self.variants.len() == 0 {
                    vec![]
                } else {
                    let (variant_type_metadata,
                         variant_llvm_type,
                         member_description_factory) =
                        describe_enum_variant(cx,
                                              self.enum_type,
                                              struct_def,
                                              &*(*self.variants)[0],
                                              NoDiscriminant,
                                              self.containing_scope,
                                              self.span);

                    let member_descriptions =
                        member_description_factory.create_member_descriptions(cx);

                    set_members_of_composite_type(cx,
                                                  variant_type_metadata,
                                                  variant_llvm_type,
                                                  &member_descriptions[..]);
                    vec![
                        MemberDescription {
                            name: "".to_string(),
                            llvm_type: variant_llvm_type,
                            type_metadata: variant_type_metadata,
                            offset: FixedMemberOffset { bytes: 0 },
                            flags: FLAGS_NONE
                        }
                    ]
                }
            }
            adt::RawNullablePointer { nndiscr: non_null_variant_index, nnty, .. } => {
                // As far as debuginfo is concerned, the pointer this enum
                // represents is still wrapped in a struct. This is to make the
                // DWARF representation of enums uniform.

                // First create a description of the artificial wrapper struct:
                let non_null_variant = &(*self.variants)[non_null_variant_index as usize];
                let non_null_variant_name = token::get_name(non_null_variant.name);

                // The llvm type and metadata of the pointer
                let non_null_llvm_type = type_of::type_of(cx, nnty);
                let non_null_type_metadata = type_metadata(cx, nnty, self.span);

                // The type of the artificial struct wrapping the pointer
                let artificial_struct_llvm_type = Type::struct_(cx,
                                                                &[non_null_llvm_type],
                                                                false);

                // For the metadata of the wrapper struct, we need to create a
                // MemberDescription of the struct's single field.
                let sole_struct_member_description = MemberDescription {
                    name: match non_null_variant.arg_names {
                        Some(ref names) => token::get_ident(names[0]).to_string(),
                        None => "".to_string()
                    },
                    llvm_type: non_null_llvm_type,
                    type_metadata: non_null_type_metadata,
                    offset: FixedMemberOffset { bytes: 0 },
                    flags: FLAGS_NONE
                };

                let unique_type_id = debug_context(cx).type_map
                                                      .borrow_mut()
                                                      .get_unique_type_id_of_enum_variant(
                                                          cx,
                                                          self.enum_type,
                                                          &non_null_variant_name);

                // Now we can create the metadata of the artificial struct
                let artificial_struct_metadata =
                    composite_type_metadata(cx,
                                            artificial_struct_llvm_type,
                                            &non_null_variant_name,
                                            unique_type_id,
                                            &[sole_struct_member_description],
                                            self.containing_scope,
                                            self.file_metadata,
                                            codemap::DUMMY_SP);

                // Encode the information about the null variant in the union
                // member's name.
                let null_variant_index = (1 - non_null_variant_index) as usize;
                let null_variant_name = token::get_name((*self.variants)[null_variant_index].name);
                let union_member_name = format!("RUST$ENCODED$ENUM${}${}",
                                                0,
                                                null_variant_name);

                // Finally create the (singleton) list of descriptions of union
                // members.
                vec![
                    MemberDescription {
                        name: union_member_name,
                        llvm_type: artificial_struct_llvm_type,
                        type_metadata: artificial_struct_metadata,
                        offset: FixedMemberOffset { bytes: 0 },
                        flags: FLAGS_NONE
                    }
                ]
            },
            adt::StructWrappedNullablePointer { nonnull: ref struct_def,
                                                nndiscr,
                                                ref discrfield, ..} => {
                // Create a description of the non-null variant
                let (variant_type_metadata, variant_llvm_type, member_description_factory) =
                    describe_enum_variant(cx,
                                          self.enum_type,
                                          struct_def,
                                          &*(*self.variants)[nndiscr as usize],
                                          OptimizedDiscriminant,
                                          self.containing_scope,
                                          self.span);

                let variant_member_descriptions =
                    member_description_factory.create_member_descriptions(cx);

                set_members_of_composite_type(cx,
                                              variant_type_metadata,
                                              variant_llvm_type,
                                              &variant_member_descriptions[..]);

                // Encode the information about the null variant in the union
                // member's name.
                let null_variant_index = (1 - nndiscr) as usize;
                let null_variant_name = token::get_name((*self.variants)[null_variant_index].name);
                let discrfield = discrfield.iter()
                                           .skip(1)
                                           .map(|x| x.to_string())
                                           .collect::<Vec<_>>().connect("$");
                let union_member_name = format!("RUST$ENCODED$ENUM${}${}",
                                                discrfield,
                                                null_variant_name);

                // Create the (singleton) list of descriptions of union members.
                vec![
                    MemberDescription {
                        name: union_member_name,
                        llvm_type: variant_llvm_type,
                        type_metadata: variant_type_metadata,
                        offset: FixedMemberOffset { bytes: 0 },
                        flags: FLAGS_NONE
                    }
                ]
            },
            adt::CEnum(..) => cx.sess().span_bug(self.span, "This should be unreachable.")
        }
    }
}

// Creates MemberDescriptions for the fields of a single enum variant.
struct VariantMemberDescriptionFactory<'tcx> {
    args: Vec<(String, Ty<'tcx>)>,
    discriminant_type_metadata: Option<DIType>,
    span: Span,
}

impl<'tcx> VariantMemberDescriptionFactory<'tcx> {
    fn create_member_descriptions<'a>(&self, cx: &CrateContext<'a, 'tcx>)
                                      -> Vec<MemberDescription> {
        self.args.iter().enumerate().map(|(i, &(ref name, ty))| {
            MemberDescription {
                name: name.to_string(),
                llvm_type: type_of::type_of(cx, ty),
                type_metadata: match self.discriminant_type_metadata {
                    Some(metadata) if i == 0 => metadata,
                    _ => type_metadata(cx, ty, self.span)
                },
                offset: ComputedMemberOffset,
                flags: FLAGS_NONE
            }
        }).collect()
    }
}

#[derive(Copy, Clone)]
enum EnumDiscriminantInfo {
    RegularDiscriminant(DIType),
    OptimizedDiscriminant,
    NoDiscriminant
}

// Returns a tuple of (1) type_metadata_stub of the variant, (2) the llvm_type
// of the variant, and (3) a MemberDescriptionFactory for producing the
// descriptions of the fields of the variant. This is a rudimentary version of a
// full RecursiveTypeDescription.
fn describe_enum_variant<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                                   enum_type: Ty<'tcx>,
                                   struct_def: &adt::Struct<'tcx>,
                                   variant_info: &ty::VariantInfo<'tcx>,
                                   discriminant_info: EnumDiscriminantInfo,
                                   containing_scope: DIScope,
                                   span: Span)
                                   -> (DICompositeType, Type, MemberDescriptionFactory<'tcx>) {
    let variant_llvm_type =
        Type::struct_(cx, &struct_def.fields
                                    .iter()
                                    .map(|&t| type_of::type_of(cx, t))
                                    .collect::<Vec<_>>()
                                    ,
                      struct_def.packed);
    // Could do some consistency checks here: size, align, field count, discr type

    let variant_name = token::get_name(variant_info.name);
    let variant_name = &variant_name;
    let unique_type_id = debug_context(cx).type_map
                                          .borrow_mut()
                                          .get_unique_type_id_of_enum_variant(
                                              cx,
                                              enum_type,
                                              variant_name);

    let metadata_stub = create_struct_stub(cx,
                                           variant_llvm_type,
                                           variant_name,
                                           unique_type_id,
                                           containing_scope);

    // Get the argument names from the enum variant info
    let mut arg_names: Vec<_> = match variant_info.arg_names {
        Some(ref names) => {
            names.iter()
                 .map(|ident| {
                     token::get_ident(*ident).to_string()
                 }).collect()
        }
        None => variant_info.args.iter().map(|_| "".to_string()).collect()
    };

    // If this is not a univariant enum, there is also the discriminant field.
    match discriminant_info {
        RegularDiscriminant(_) => arg_names.insert(0, "RUST$ENUM$DISR".to_string()),
        _ => { /* do nothing */ }
    };

    // Build an array of (field name, field type) pairs to be captured in the factory closure.
    let args: Vec<(String, Ty)> = arg_names.iter()
        .zip(struct_def.fields.iter())
        .map(|(s, &t)| (s.to_string(), t))
        .collect();

    let member_description_factory =
        VariantMDF(VariantMemberDescriptionFactory {
            args: args,
            discriminant_type_metadata: match discriminant_info {
                RegularDiscriminant(discriminant_type_metadata) => {
                    Some(discriminant_type_metadata)
                }
                _ => None
            },
            span: span,
        });

    (metadata_stub, variant_llvm_type, member_description_factory)
}

fn prepare_enum_metadata<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                                   enum_type: Ty<'tcx>,
                                   enum_def_id: ast::DefId,
                                   unique_type_id: UniqueTypeId,
                                   span: Span)
                                   -> RecursiveTypeDescription<'tcx> {
    let enum_name = compute_debuginfo_type_name(cx, enum_type, false);

    let (containing_scope, definition_span) = get_namespace_and_span_for_item(cx, enum_def_id);
    let loc = span_start(cx, definition_span);
    let file_metadata = file_metadata(cx, &loc.file.name);

    let variants = ty::enum_variants(cx.tcx(), enum_def_id);

    let enumerators_metadata: Vec<DIDescriptor> = variants
        .iter()
        .map(|v| {
            let token = token::get_name(v.name);
            let name = CString::new(token.as_bytes()).unwrap();
            unsafe {
                llvm::LLVMDIBuilderCreateEnumerator(
                    DIB(cx),
                    name.as_ptr(),
                    v.disr_val as u64)
            }
        })
        .collect();

    let discriminant_type_metadata = |inttype| {
        // We can reuse the type of the discriminant for all monomorphized
        // instances of an enum because it doesn't depend on any type parameters.
        // The def_id, uniquely identifying the enum's polytype acts as key in
        // this cache.
        let cached_discriminant_type_metadata = debug_context(cx).created_enum_disr_types
                                                                 .borrow()
                                                                 .get(&enum_def_id).cloned();
        match cached_discriminant_type_metadata {
            Some(discriminant_type_metadata) => discriminant_type_metadata,
            None => {
                let discriminant_llvm_type = adt::ll_inttype(cx, inttype);
                let (discriminant_size, discriminant_align) =
                    size_and_align_of(cx, discriminant_llvm_type);
                let discriminant_base_type_metadata =
                    type_metadata(cx,
                                  adt::ty_of_inttype(cx.tcx(), inttype),
                                  codemap::DUMMY_SP);
                let discriminant_name = get_enum_discriminant_name(cx, enum_def_id);

                let name = CString::new(discriminant_name.as_bytes()).unwrap();
                let discriminant_type_metadata = unsafe {
                    llvm::LLVMDIBuilderCreateEnumerationType(
                        DIB(cx),
                        containing_scope,
                        name.as_ptr(),
                        UNKNOWN_FILE_METADATA,
                        UNKNOWN_LINE_NUMBER,
                        bytes_to_bits(discriminant_size),
                        bytes_to_bits(discriminant_align),
                        create_DIArray(DIB(cx), &enumerators_metadata),
                        discriminant_base_type_metadata)
                };

                debug_context(cx).created_enum_disr_types
                                 .borrow_mut()
                                 .insert(enum_def_id, discriminant_type_metadata);

                discriminant_type_metadata
            }
        }
    };

    let type_rep = adt::represent_type(cx, enum_type);

    let discriminant_type_metadata = match *type_rep {
        adt::CEnum(inttype, _, _) => {
            return FinalMetadata(discriminant_type_metadata(inttype))
        },
        adt::RawNullablePointer { .. }           |
        adt::StructWrappedNullablePointer { .. } |
        adt::Univariant(..)                      => None,
        adt::General(inttype, _, _) => Some(discriminant_type_metadata(inttype)),
    };

    let enum_llvm_type = type_of::type_of(cx, enum_type);
    let (enum_type_size, enum_type_align) = size_and_align_of(cx, enum_llvm_type);

    let unique_type_id_str = debug_context(cx)
                             .type_map
                             .borrow()
                             .get_unique_type_id_as_string(unique_type_id);

    let enum_name = CString::new(enum_name).unwrap();
    let unique_type_id_str = CString::new(unique_type_id_str.as_bytes()).unwrap();
    let enum_metadata = unsafe {
        llvm::LLVMDIBuilderCreateUnionType(
        DIB(cx),
        containing_scope,
        enum_name.as_ptr(),
        UNKNOWN_FILE_METADATA,
        UNKNOWN_LINE_NUMBER,
        bytes_to_bits(enum_type_size),
        bytes_to_bits(enum_type_align),
        0, // Flags
        ptr::null_mut(),
        0, // RuntimeLang
        unique_type_id_str.as_ptr())
    };

    return create_and_register_recursive_type_forward_declaration(
        cx,
        enum_type,
        unique_type_id,
        enum_metadata,
        enum_llvm_type,
        EnumMDF(EnumMemberDescriptionFactory {
            enum_type: enum_type,
            type_rep: type_rep.clone(),
            variants: variants,
            discriminant_type_metadata: discriminant_type_metadata,
            containing_scope: containing_scope,
            file_metadata: file_metadata,
            span: span,
        }),
    );

    fn get_enum_discriminant_name(cx: &CrateContext,
                                  def_id: ast::DefId)
                                  -> token::InternedString {
        let name = if def_id.krate == ast::LOCAL_CRATE {
            cx.tcx().map.get_path_elem(def_id.node).name()
        } else {
            csearch::get_item_path(cx.tcx(), def_id).last().unwrap().name()
        };

        token::get_name(name)
    }
}

/// Creates debug information for a composite type, that is, anything that
/// results in a LLVM struct.
///
/// Examples of Rust types to use this are: structs, tuples, boxes, vecs, and enums.
fn composite_type_metadata(cx: &CrateContext,
                           composite_llvm_type: Type,
                           composite_type_name: &str,
                           composite_type_unique_id: UniqueTypeId,
                           member_descriptions: &[MemberDescription],
                           containing_scope: DIScope,

                           // Ignore source location information as long as it
                           // can't be reconstructed for non-local crates.
                           _file_metadata: DIFile,
                           _definition_span: Span)
                        -> DICompositeType {
    // Create the (empty) struct metadata node ...
    let composite_type_metadata = create_struct_stub(cx,
                                                     composite_llvm_type,
                                                     composite_type_name,
                                                     composite_type_unique_id,
                                                     containing_scope);
    // ... and immediately create and add the member descriptions.
    set_members_of_composite_type(cx,
                                  composite_type_metadata,
                                  composite_llvm_type,
                                  member_descriptions);

    return composite_type_metadata;
}

fn set_members_of_composite_type(cx: &CrateContext,
                                 composite_type_metadata: DICompositeType,
                                 composite_llvm_type: Type,
                                 member_descriptions: &[MemberDescription]) {
    // In some rare cases LLVM metadata uniquing would lead to an existing type
    // description being used instead of a new one created in create_struct_stub.
    // This would cause a hard to trace assertion in DICompositeType::SetTypeArray().
    // The following check makes sure that we get a better error message if this
    // should happen again due to some regression.
    {
        let mut composite_types_completed =
            debug_context(cx).composite_types_completed.borrow_mut();
        if composite_types_completed.contains(&composite_type_metadata) {
            let (llvm_version_major, llvm_version_minor) = unsafe {
                (llvm::LLVMVersionMajor(), llvm::LLVMVersionMinor())
            };

            let actual_llvm_version = llvm_version_major * 1000000 + llvm_version_minor * 1000;
            let min_supported_llvm_version = 3 * 1000000 + 4 * 1000;

            if actual_llvm_version < min_supported_llvm_version {
                cx.sess().warn(&format!("This version of rustc was built with LLVM \
                                        {}.{}. Rustc just ran into a known \
                                        debuginfo corruption problem thatoften \
                                        occurs with LLVM versions below 3.4. \
                                        Please use a rustc built with anewer \
                                        version of LLVM.",
                                       llvm_version_major,
                                       llvm_version_minor));
            } else {
                cx.sess().bug("debuginfo::set_members_of_composite_type() - \
                               Already completed forward declaration re-encountered.");
            }
        } else {
            composite_types_completed.insert(composite_type_metadata);
        }
    }

    let member_metadata: Vec<DIDescriptor> = member_descriptions
        .iter()
        .enumerate()
        .map(|(i, member_description)| {
            let (member_size, member_align) = size_and_align_of(cx, member_description.llvm_type);
            let member_offset = match member_description.offset {
                FixedMemberOffset { bytes } => bytes as u64,
                ComputedMemberOffset => machine::llelement_offset(cx, composite_llvm_type, i)
            };

            let member_name = member_description.name.as_bytes();
            let member_name = CString::new(member_name).unwrap();
            unsafe {
                llvm::LLVMDIBuilderCreateMemberType(
                    DIB(cx),
                    composite_type_metadata,
                    member_name.as_ptr(),
                    UNKNOWN_FILE_METADATA,
                    UNKNOWN_LINE_NUMBER,
                    bytes_to_bits(member_size),
                    bytes_to_bits(member_align),
                    bytes_to_bits(member_offset),
                    member_description.flags,
                    member_description.type_metadata)
            }
        })
        .collect();

    unsafe {
        let type_array = create_DIArray(DIB(cx), &member_metadata[..]);
        llvm::LLVMDICompositeTypeSetTypeArray(DIB(cx), composite_type_metadata, type_array);
    }
}

// A convenience wrapper around LLVMDIBuilderCreateStructType(). Does not do any
// caching, does not add any fields to the struct. This can be done later with
// set_members_of_composite_type().
fn create_struct_stub(cx: &CrateContext,
                      struct_llvm_type: Type,
                      struct_type_name: &str,
                      unique_type_id: UniqueTypeId,
                      containing_scope: DIScope)
                   -> DICompositeType {
    let (struct_size, struct_align) = size_and_align_of(cx, struct_llvm_type);

    let unique_type_id_str = debug_context(cx).type_map
                                              .borrow()
                                              .get_unique_type_id_as_string(unique_type_id);
    let name = CString::new(struct_type_name).unwrap();
    let unique_type_id = CString::new(unique_type_id_str.as_bytes()).unwrap();
    let metadata_stub = unsafe {
        // LLVMDIBuilderCreateStructType() wants an empty array. A null
        // pointer will lead to hard to trace and debug LLVM assertions
        // later on in llvm/lib/IR/Value.cpp.
        let empty_array = create_DIArray(DIB(cx), &[]);

        llvm::LLVMDIBuilderCreateStructType(
            DIB(cx),
            containing_scope,
            name.as_ptr(),
            UNKNOWN_FILE_METADATA,
            UNKNOWN_LINE_NUMBER,
            bytes_to_bits(struct_size),
            bytes_to_bits(struct_align),
            0,
            ptr::null_mut(),
            empty_array,
            0,
            ptr::null_mut(),
            unique_type_id.as_ptr())
    };

    return metadata_stub;
}

fn fixed_vec_metadata<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                                unique_type_id: UniqueTypeId,
                                element_type: Ty<'tcx>,
                                len: Option<u64>,
                                span: Span)
                                -> MetadataCreationResult {
    let element_type_metadata = type_metadata(cx, element_type, span);

    return_if_metadata_created_in_meantime!(cx, unique_type_id);

    let element_llvm_type = type_of::type_of(cx, element_type);
    let (element_type_size, element_type_align) = size_and_align_of(cx, element_llvm_type);

    let (array_size_in_bytes, upper_bound) = match len {
        Some(len) => (element_type_size * len, len as c_longlong),
        None => (0, -1)
    };

    let subrange = unsafe {
        llvm::LLVMDIBuilderGetOrCreateSubrange(DIB(cx), 0, upper_bound)
    };

    let subscripts = create_DIArray(DIB(cx), &[subrange]);
    let metadata = unsafe {
        llvm::LLVMDIBuilderCreateArrayType(
            DIB(cx),
            bytes_to_bits(array_size_in_bytes),
            bytes_to_bits(element_type_align),
            element_type_metadata,
            subscripts)
    };

    return MetadataCreationResult::new(metadata, false);
}

fn vec_slice_metadata<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                                vec_type: Ty<'tcx>,
                                element_type: Ty<'tcx>,
                                unique_type_id: UniqueTypeId,
                                span: Span)
                                -> MetadataCreationResult {
    let data_ptr_type = ty::mk_ptr(cx.tcx(), ty::mt {
        ty: element_type,
        mutbl: ast::MutImmutable
    });

    let element_type_metadata = type_metadata(cx, data_ptr_type, span);

    return_if_metadata_created_in_meantime!(cx, unique_type_id);

    let slice_llvm_type = type_of::type_of(cx, vec_type);
    let slice_type_name = compute_debuginfo_type_name(cx, vec_type, true);

    let member_llvm_types = slice_llvm_type.field_types();
    assert!(slice_layout_is_correct(cx,
                                    &member_llvm_types[..],
                                    element_type));
    let member_descriptions = [
        MemberDescription {
            name: "data_ptr".to_string(),
            llvm_type: member_llvm_types[0],
            type_metadata: element_type_metadata,
            offset: ComputedMemberOffset,
            flags: FLAGS_NONE
        },
        MemberDescription {
            name: "length".to_string(),
            llvm_type: member_llvm_types[1],
            type_metadata: type_metadata(cx, cx.tcx().types.usize, span),
            offset: ComputedMemberOffset,
            flags: FLAGS_NONE
        },
    ];

    assert!(member_descriptions.len() == member_llvm_types.len());

    let loc = span_start(cx, span);
    let file_metadata = file_metadata(cx, &loc.file.name);

    let metadata = composite_type_metadata(cx,
                                           slice_llvm_type,
                                           &slice_type_name[..],
                                           unique_type_id,
                                           &member_descriptions,
                                           UNKNOWN_SCOPE_METADATA,
                                           file_metadata,
                                           span);
    return MetadataCreationResult::new(metadata, false);

    fn slice_layout_is_correct<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                                         member_llvm_types: &[Type],
                                         element_type: Ty<'tcx>)
                                         -> bool {
        member_llvm_types.len() == 2 &&
        member_llvm_types[0] == type_of::type_of(cx, element_type).ptr_to() &&
        member_llvm_types[1] == cx.int_type()
    }
}

fn subroutine_type_metadata<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                                      unique_type_id: UniqueTypeId,
                                      signature: &ty::PolyFnSig<'tcx>,
                                      span: Span)
                                      -> MetadataCreationResult
{
    let signature = ty::erase_late_bound_regions(cx.tcx(), signature);

    let mut signature_metadata: Vec<DIType> = Vec::with_capacity(signature.inputs.len() + 1);

    // return type
    signature_metadata.push(match signature.output {
        ty::FnConverging(ret_ty) => match ret_ty.sty {
            ty::ty_tup(ref tys) if tys.is_empty() => ptr::null_mut(),
            _ => type_metadata(cx, ret_ty, span)
        },
        ty::FnDiverging => diverging_type_metadata(cx)
    });

    // regular arguments
    for &argument_type in &signature.inputs {
        signature_metadata.push(type_metadata(cx, argument_type, span));
    }

    return_if_metadata_created_in_meantime!(cx, unique_type_id);

    return MetadataCreationResult::new(
        unsafe {
            llvm::LLVMDIBuilderCreateSubroutineType(
                DIB(cx),
                UNKNOWN_FILE_METADATA,
                create_DIArray(DIB(cx), &signature_metadata[..]))
        },
        false);
}

// FIXME(1563) This is all a bit of a hack because 'trait pointer' is an ill-
// defined concept. For the case of an actual trait pointer (i.e., Box<Trait>,
// &Trait), trait_object_type should be the whole thing (e.g, Box<Trait>) and
// trait_type should be the actual trait (e.g., Trait). Where the trait is part
// of a DST struct, there is no trait_object_type and the results of this
// function will be a little bit weird.
fn trait_pointer_metadata<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                                    trait_type: Ty<'tcx>,
                                    trait_object_type: Option<Ty<'tcx>>,
                                    unique_type_id: UniqueTypeId)
                                    -> DIType {
    // The implementation provided here is a stub. It makes sure that the trait
    // type is assigned the correct name, size, namespace, and source location.
    // But it does not describe the trait's methods.

    let def_id = match trait_type.sty {
        ty::ty_trait(ref data) => data.principal_def_id(),
        _ => {
            let pp_type_name = ppaux::ty_to_string(cx.tcx(), trait_type);
            cx.sess().bug(&format!("debuginfo: Unexpected trait-object type in \
                                   trait_pointer_metadata(): {}",
                                   &pp_type_name[..]));
        }
    };

    let trait_object_type = trait_object_type.unwrap_or(trait_type);
    let trait_type_name =
        compute_debuginfo_type_name(cx, trait_object_type, false);

    let (containing_scope, _) = get_namespace_and_span_for_item(cx, def_id);

    let trait_llvm_type = type_of::type_of(cx, trait_object_type);

    composite_type_metadata(cx,
                            trait_llvm_type,
                            &trait_type_name[..],
                            unique_type_id,
                            &[],
                            containing_scope,
                            UNKNOWN_FILE_METADATA,
                            codemap::DUMMY_SP)
}

fn type_metadata<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                           t: Ty<'tcx>,
                           usage_site_span: Span)
                           -> DIType {
    // Get the unique type id of this type.
    let unique_type_id = {
        let mut type_map = debug_context(cx).type_map.borrow_mut();
        // First, try to find the type in TypeMap. If we have seen it before, we
        // can exit early here.
        match type_map.find_metadata_for_type(t) {
            Some(metadata) => {
                return metadata;
            },
            None => {
                // The Ty is not in the TypeMap but maybe we have already seen
                // an equivalent type (e.g. only differing in region arguments).
                // In order to find out, generate the unique type id and look
                // that up.
                let unique_type_id = type_map.get_unique_type_id_of_type(cx, t);
                match type_map.find_metadata_for_unique_id(unique_type_id) {
                    Some(metadata) => {
                        // There is already an equivalent type in the TypeMap.
                        // Register this Ty as an alias in the cache and
                        // return the cached metadata.
                        type_map.register_type_with_metadata(cx, t, metadata);
                        return metadata;
                    },
                    None => {
                        // There really is no type metadata for this type, so
                        // proceed by creating it.
                        unique_type_id
                    }
                }
            }
        }
    };

    debug!("type_metadata: {:?}", t);

    let sty = &t.sty;
    let MetadataCreationResult { metadata, already_stored_in_typemap } = match *sty {
        ty::ty_bool     |
        ty::ty_char     |
        ty::ty_int(_)   |
        ty::ty_uint(_)  |
        ty::ty_float(_) => {
            MetadataCreationResult::new(basic_type_metadata(cx, t), false)
        }
        ty::ty_tup(ref elements) if elements.is_empty() => {
            MetadataCreationResult::new(basic_type_metadata(cx, t), false)
        }
        ty::ty_enum(def_id, _) => {
            prepare_enum_metadata(cx, t, def_id, unique_type_id, usage_site_span).finalize(cx)
        }
        ty::ty_vec(typ, len) => {
            fixed_vec_metadata(cx, unique_type_id, typ, len.map(|x| x as u64), usage_site_span)
        }
        ty::ty_str => {
            fixed_vec_metadata(cx, unique_type_id, cx.tcx().types.i8, None, usage_site_span)
        }
        ty::ty_trait(..) => {
            MetadataCreationResult::new(
                        trait_pointer_metadata(cx, t, None, unique_type_id),
            false)
        }
        ty::ty_uniq(ty) | ty::ty_ptr(ty::mt{ty, ..}) | ty::ty_rptr(_, ty::mt{ty, ..}) => {
            match ty.sty {
                ty::ty_vec(typ, None) => {
                    vec_slice_metadata(cx, t, typ, unique_type_id, usage_site_span)
                }
                ty::ty_str => {
                    vec_slice_metadata(cx, t, cx.tcx().types.u8, unique_type_id, usage_site_span)
                }
                ty::ty_trait(..) => {
                    MetadataCreationResult::new(
                        trait_pointer_metadata(cx, ty, Some(t), unique_type_id),
                        false)
                }
                _ => {
                    let pointee_metadata = type_metadata(cx, ty, usage_site_span);

                    match debug_context(cx).type_map
                                           .borrow()
                                           .find_metadata_for_unique_id(unique_type_id) {
                        Some(metadata) => return metadata,
                        None => { /* proceed normally */ }
                    };

                    MetadataCreationResult::new(pointer_type_metadata(cx, t, pointee_metadata),
                                                false)
                }
            }
        }
        ty::ty_bare_fn(_, ref barefnty) => {
            subroutine_type_metadata(cx, unique_type_id, &barefnty.sig, usage_site_span)
        }
        ty::ty_closure(def_id, substs) => {
            let typer = NormalizingClosureTyper::new(cx.tcx());
            let sig = typer.closure_type(def_id, substs).sig;
            subroutine_type_metadata(cx, unique_type_id, &sig, usage_site_span)
        }
        ty::ty_struct(def_id, substs) => {
            prepare_struct_metadata(cx,
                                    t,
                                    def_id,
                                    substs,
                                    unique_type_id,
                                    usage_site_span).finalize(cx)
        }
        ty::ty_tup(ref elements) => {
            prepare_tuple_metadata(cx,
                                   t,
                                   &elements[..],
                                   unique_type_id,
                                   usage_site_span).finalize(cx)
        }
        _ => {
            cx.sess().bug(&format!("debuginfo: unexpected type in type_metadata: {:?}",
                                  sty))
        }
    };

    {
        let mut type_map = debug_context(cx).type_map.borrow_mut();

        if already_stored_in_typemap {
            // Also make sure that we already have a TypeMap entry entry for the unique type id.
            let metadata_for_uid = match type_map.find_metadata_for_unique_id(unique_type_id) {
                Some(metadata) => metadata,
                None => {
                    let unique_type_id_str =
                        type_map.get_unique_type_id_as_string(unique_type_id);
                    let error_message = format!("Expected type metadata for unique \
                                                 type id '{}' to already be in \
                                                 the debuginfo::TypeMap but it \
                                                 was not. (Ty = {})",
                                                &unique_type_id_str[..],
                                                ppaux::ty_to_string(cx.tcx(), t));
                    cx.sess().span_bug(usage_site_span, &error_message[..]);
                }
            };

            match type_map.find_metadata_for_type(t) {
                Some(metadata) => {
                    if metadata != metadata_for_uid {
                        let unique_type_id_str =
                            type_map.get_unique_type_id_as_string(unique_type_id);
                        let error_message = format!("Mismatch between Ty and \
                                                     UniqueTypeId maps in \
                                                     debuginfo::TypeMap. \
                                                     UniqueTypeId={}, Ty={}",
                            &unique_type_id_str[..],
                            ppaux::ty_to_string(cx.tcx(), t));
                        cx.sess().span_bug(usage_site_span, &error_message[..]);
                    }
                }
                None => {
                    type_map.register_type_with_metadata(cx, t, metadata);
                }
            }
        } else {
            type_map.register_type_with_metadata(cx, t, metadata);
            type_map.register_unique_id_with_metadata(cx, unique_type_id, metadata);
        }
    }

    metadata
}

struct MetadataCreationResult {
    metadata: DIType,
    already_stored_in_typemap: bool
}

impl MetadataCreationResult {
    fn new(metadata: DIType, already_stored_in_typemap: bool) -> MetadataCreationResult {
        MetadataCreationResult {
            metadata: metadata,
            already_stored_in_typemap: already_stored_in_typemap
        }
    }
}

#[derive(Copy, Clone, PartialEq)]
enum InternalDebugLocation {
    KnownLocation { scope: DIScope, line: usize, col: usize },
    UnknownLocation
}

impl InternalDebugLocation {
    fn new(scope: DIScope, line: usize, col: usize) -> InternalDebugLocation {
        KnownLocation {
            scope: scope,
            line: line,
            col: col,
        }
    }
}

fn set_debug_location(cx: &CrateContext, debug_location: InternalDebugLocation) {
    if debug_location == debug_context(cx).current_debug_location.get() {
        return;
    }

    let metadata_node;

    match debug_location {
        KnownLocation { scope, line, .. } => {
            // Always set the column to zero like Clang and GCC
            let col = UNKNOWN_COLUMN_NUMBER;
            debug!("setting debug location to {} {}", line, col);

            unsafe {
                metadata_node = llvm::LLVMDIBuilderCreateDebugLocation(
                    debug_context(cx).llcontext,
                    line as c_uint,
                    col as c_uint,
                    scope,
                    ptr::null_mut());
            }
        }
        UnknownLocation => {
            debug!("clearing debug location ");
            metadata_node = ptr::null_mut();
        }
    };

    unsafe {
        llvm::LLVMSetCurrentDebugLocation(cx.raw_builder(), metadata_node);
    }

    debug_context(cx).current_debug_location.set(debug_location);
}

//=-----------------------------------------------------------------------------
//  Utility Functions
//=-----------------------------------------------------------------------------

fn contains_nodebug_attribute(attributes: &[ast::Attribute]) -> bool {
    attributes.iter().any(|attr| {
        let meta_item: &ast::MetaItem = &*attr.node.value;
        match meta_item.node {
            ast::MetaWord(ref value) => &value[..] == "no_debug",
            _ => false
        }
    })
}

/// Return codemap::Loc corresponding to the beginning of the span
fn span_start(cx: &CrateContext, span: Span) -> codemap::Loc {
    cx.sess().codemap().lookup_char_pos(span.lo)
}

fn size_and_align_of(cx: &CrateContext, llvm_type: Type) -> (u64, u64) {
    (machine::llsize_of_alloc(cx, llvm_type), machine::llalign_of_min(cx, llvm_type) as u64)
}

fn bytes_to_bits(bytes: u64) -> u64 {
    bytes * 8
}

#[inline]
fn debug_context<'a, 'tcx>(cx: &'a CrateContext<'a, 'tcx>)
                           -> &'a CrateDebugContext<'tcx> {
    let debug_context: &'a CrateDebugContext<'tcx> = cx.dbg_cx().as_ref().unwrap();
    debug_context
}

#[inline]
#[allow(non_snake_case)]
fn DIB(cx: &CrateContext) -> DIBuilderRef {
    cx.dbg_cx().as_ref().unwrap().builder
}

fn fn_should_be_ignored(fcx: &FunctionContext) -> bool {
    match fcx.debug_context {
        FunctionDebugContext::RegularContext(_) => false,
        _ => true
    }
}

fn assert_type_for_node_id(cx: &CrateContext,
                           node_id: ast::NodeId,
                           error_reporting_span: Span) {
    if !cx.tcx().node_types().contains_key(&node_id) {
        cx.sess().span_bug(error_reporting_span,
                           "debuginfo: Could not find type for node id!");
    }
}

fn get_namespace_and_span_for_item(cx: &CrateContext, def_id: ast::DefId)
                                   -> (DIScope, Span) {
    let containing_scope = namespace_for_item(cx, def_id).scope;
    let definition_span = if def_id.krate == ast::LOCAL_CRATE {
        cx.tcx().map.span(def_id.node)
    } else {
        // For external items there is no span information
        codemap::DUMMY_SP
    };

    (containing_scope, definition_span)
}

// This procedure builds the *scope map* for a given function, which maps any
// given ast::NodeId in the function's AST to the correct DIScope metadata instance.
//
// This builder procedure walks the AST in execution order and keeps track of
// what belongs to which scope, creating DIScope DIEs along the way, and
// introducing *artificial* lexical scope descriptors where necessary. These
// artificial scopes allow GDB to correctly handle name shadowing.
fn create_scope_map(cx: &CrateContext,
                    args: &[ast::Arg],
                    fn_entry_block: &ast::Block,
                    fn_metadata: DISubprogram,
                    fn_ast_id: ast::NodeId)
                 -> NodeMap<DIScope> {
    let mut scope_map = NodeMap();

    let def_map = &cx.tcx().def_map;

    struct ScopeStackEntry {
        scope_metadata: DIScope,
        ident: Option<ast::Ident>
    }

    let mut scope_stack = vec!(ScopeStackEntry { scope_metadata: fn_metadata,
                                                 ident: None });
    scope_map.insert(fn_ast_id, fn_metadata);

    // Push argument identifiers onto the stack so arguments integrate nicely
    // with variable shadowing.
    for arg in args {
        pat_util::pat_bindings(def_map, &*arg.pat, |_, node_id, _, path1| {
            scope_stack.push(ScopeStackEntry { scope_metadata: fn_metadata,
                                               ident: Some(path1.node) });
            scope_map.insert(node_id, fn_metadata);
        })
    }

    // Clang creates a separate scope for function bodies, so let's do this too.
    with_new_scope(cx,
                   fn_entry_block.span,
                   &mut scope_stack,
                   &mut scope_map,
                   |cx, scope_stack, scope_map| {
        walk_block(cx, fn_entry_block, scope_stack, scope_map);
    });

    return scope_map;


    // local helper functions for walking the AST.
    fn with_new_scope<F>(cx: &CrateContext,
                         scope_span: Span,
                         scope_stack: &mut Vec<ScopeStackEntry> ,
                         scope_map: &mut NodeMap<DIScope>,
                         inner_walk: F) where
        F: FnOnce(&CrateContext, &mut Vec<ScopeStackEntry>, &mut NodeMap<DIScope>),
    {
        // Create a new lexical scope and push it onto the stack
        let loc = cx.sess().codemap().lookup_char_pos(scope_span.lo);
        let file_metadata = file_metadata(cx, &loc.file.name);
        let parent_scope = scope_stack.last().unwrap().scope_metadata;

        let scope_metadata = unsafe {
            llvm::LLVMDIBuilderCreateLexicalBlock(
                DIB(cx),
                parent_scope,
                file_metadata,
                loc.line as c_uint,
                loc.col.to_usize() as c_uint)
        };

        scope_stack.push(ScopeStackEntry { scope_metadata: scope_metadata,
                                           ident: None });

        inner_walk(cx, scope_stack, scope_map);

        // pop artificial scopes
        while scope_stack.last().unwrap().ident.is_some() {
            scope_stack.pop();
        }

        if scope_stack.last().unwrap().scope_metadata != scope_metadata {
            cx.sess().span_bug(scope_span, "debuginfo: Inconsistency in scope management.");
        }

        scope_stack.pop();
    }

    fn walk_block(cx: &CrateContext,
                  block: &ast::Block,
                  scope_stack: &mut Vec<ScopeStackEntry> ,
                  scope_map: &mut NodeMap<DIScope>) {
        scope_map.insert(block.id, scope_stack.last().unwrap().scope_metadata);

        // The interesting things here are statements and the concluding expression.
        for statement in &block.stmts {
            scope_map.insert(ast_util::stmt_id(&**statement),
                             scope_stack.last().unwrap().scope_metadata);

            match statement.node {
                ast::StmtDecl(ref decl, _) =>
                    walk_decl(cx, &**decl, scope_stack, scope_map),
                ast::StmtExpr(ref exp, _) |
                ast::StmtSemi(ref exp, _) =>
                    walk_expr(cx, &**exp, scope_stack, scope_map),
                ast::StmtMac(..) => () // Ignore macros (which should be expanded anyway).
            }
        }

        if let Some(ref exp) = block.expr {
            walk_expr(cx, &**exp, scope_stack, scope_map);
        }
    }

    fn walk_decl(cx: &CrateContext,
                 decl: &ast::Decl,
                 scope_stack: &mut Vec<ScopeStackEntry> ,
                 scope_map: &mut NodeMap<DIScope>) {
        match *decl {
            codemap::Spanned { node: ast::DeclLocal(ref local), .. } => {
                scope_map.insert(local.id, scope_stack.last().unwrap().scope_metadata);

                walk_pattern(cx, &*local.pat, scope_stack, scope_map);

                if let Some(ref exp) = local.init {
                    walk_expr(cx, &**exp, scope_stack, scope_map);
                }
            }
            _ => ()
        }
    }

    fn walk_pattern(cx: &CrateContext,
                    pat: &ast::Pat,
                    scope_stack: &mut Vec<ScopeStackEntry> ,
                    scope_map: &mut NodeMap<DIScope>) {

        let def_map = &cx.tcx().def_map;

        // Unfortunately, we cannot just use pat_util::pat_bindings() or
        // ast_util::walk_pat() here because we have to visit *all* nodes in
        // order to put them into the scope map. The above functions don't do that.
        match pat.node {
            ast::PatIdent(_, ref path1, ref sub_pat_opt) => {

                // Check if this is a binding. If so we need to put it on the
                // scope stack and maybe introduce an artificial scope
                if pat_util::pat_is_binding(def_map, &*pat) {

                    let ident = path1.node;

                    // LLVM does not properly generate 'DW_AT_start_scope' fields
                    // for variable DIEs. For this reason we have to introduce
                    // an artificial scope at bindings whenever a variable with
                    // the same name is declared in *any* parent scope.
                    //
                    // Otherwise the following error occurs:
                    //
                    // let x = 10;
                    //
                    // do_something(); // 'gdb print x' correctly prints 10
                    //
                    // {
                    //     do_something(); // 'gdb print x' prints 0, because it
                    //                     // already reads the uninitialized 'x'
                    //                     // from the next line...
                    //     let x = 100;
                    //     do_something(); // 'gdb print x' correctly prints 100
                    // }

                    // Is there already a binding with that name?
                    // N.B.: this comparison must be UNhygienic... because
                    // gdb knows nothing about the context, so any two
                    // variables with the same name will cause the problem.
                    let need_new_scope = scope_stack
                        .iter()
                        .any(|entry| entry.ident.iter().any(|i| i.name == ident.name));

                    if need_new_scope {
                        // Create a new lexical scope and push it onto the stack
                        let loc = cx.sess().codemap().lookup_char_pos(pat.span.lo);
                        let file_metadata = file_metadata(cx, &loc.file.name);
                        let parent_scope = scope_stack.last().unwrap().scope_metadata;

                        let scope_metadata = unsafe {
                            llvm::LLVMDIBuilderCreateLexicalBlock(
                                DIB(cx),
                                parent_scope,
                                file_metadata,
                                loc.line as c_uint,
                                loc.col.to_usize() as c_uint)
                        };

                        scope_stack.push(ScopeStackEntry {
                            scope_metadata: scope_metadata,
                            ident: Some(ident)
                        });

                    } else {
                        // Push a new entry anyway so the name can be found
                        let prev_metadata = scope_stack.last().unwrap().scope_metadata;
                        scope_stack.push(ScopeStackEntry {
                            scope_metadata: prev_metadata,
                            ident: Some(ident)
                        });
                    }
                }

                scope_map.insert(pat.id, scope_stack.last().unwrap().scope_metadata);

                if let Some(ref sub_pat) = *sub_pat_opt {
                    walk_pattern(cx, &**sub_pat, scope_stack, scope_map);
                }
            }

            ast::PatWild(_) => {
                scope_map.insert(pat.id, scope_stack.last().unwrap().scope_metadata);
            }

            ast::PatEnum(_, ref sub_pats_opt) => {
                scope_map.insert(pat.id, scope_stack.last().unwrap().scope_metadata);

                if let Some(ref sub_pats) = *sub_pats_opt {
                    for p in sub_pats {
                        walk_pattern(cx, &**p, scope_stack, scope_map);
                    }
                }
            }

            ast::PatStruct(_, ref field_pats, _) => {
                scope_map.insert(pat.id, scope_stack.last().unwrap().scope_metadata);

                for &codemap::Spanned {
                    node: ast::FieldPat { pat: ref sub_pat, .. },
                    ..
                } in field_pats.iter() {
                    walk_pattern(cx, &**sub_pat, scope_stack, scope_map);
                }
            }

            ast::PatTup(ref sub_pats) => {
                scope_map.insert(pat.id, scope_stack.last().unwrap().scope_metadata);

                for sub_pat in sub_pats {
                    walk_pattern(cx, &**sub_pat, scope_stack, scope_map);
                }
            }

            ast::PatBox(ref sub_pat) | ast::PatRegion(ref sub_pat, _) => {
                scope_map.insert(pat.id, scope_stack.last().unwrap().scope_metadata);
                walk_pattern(cx, &**sub_pat, scope_stack, scope_map);
            }

            ast::PatLit(ref exp) => {
                scope_map.insert(pat.id, scope_stack.last().unwrap().scope_metadata);
                walk_expr(cx, &**exp, scope_stack, scope_map);
            }

            ast::PatRange(ref exp1, ref exp2) => {
                scope_map.insert(pat.id, scope_stack.last().unwrap().scope_metadata);
                walk_expr(cx, &**exp1, scope_stack, scope_map);
                walk_expr(cx, &**exp2, scope_stack, scope_map);
            }

            ast::PatVec(ref front_sub_pats, ref middle_sub_pats, ref back_sub_pats) => {
                scope_map.insert(pat.id, scope_stack.last().unwrap().scope_metadata);

                for sub_pat in front_sub_pats {
                    walk_pattern(cx, &**sub_pat, scope_stack, scope_map);
                }

                if let Some(ref sub_pat) = *middle_sub_pats {
                    walk_pattern(cx, &**sub_pat, scope_stack, scope_map);
                }

                for sub_pat in back_sub_pats {
                    walk_pattern(cx, &**sub_pat, scope_stack, scope_map);
                }
            }

            ast::PatMac(_) => {
                cx.sess().span_bug(pat.span, "debuginfo::create_scope_map() - \
                                              Found unexpanded macro.");
            }
        }
    }

    fn walk_expr(cx: &CrateContext,
                 exp: &ast::Expr,
                 scope_stack: &mut Vec<ScopeStackEntry> ,
                 scope_map: &mut NodeMap<DIScope>) {

        scope_map.insert(exp.id, scope_stack.last().unwrap().scope_metadata);

        match exp.node {
            ast::ExprLit(_)   |
            ast::ExprBreak(_) |
            ast::ExprAgain(_) |
            ast::ExprPath(..) => {}

            ast::ExprCast(ref sub_exp, _)     |
            ast::ExprAddrOf(_, ref sub_exp)  |
            ast::ExprField(ref sub_exp, _) |
            ast::ExprTupField(ref sub_exp, _) |
            ast::ExprParen(ref sub_exp) =>
                walk_expr(cx, &**sub_exp, scope_stack, scope_map),

            ast::ExprBox(ref place, ref sub_expr) => {
                place.as_ref().map(
                    |e| walk_expr(cx, &**e, scope_stack, scope_map));
                walk_expr(cx, &**sub_expr, scope_stack, scope_map);
            }

            ast::ExprRet(ref exp_opt) => match *exp_opt {
                Some(ref sub_exp) => walk_expr(cx, &**sub_exp, scope_stack, scope_map),
                None => ()
            },

            ast::ExprUnary(_, ref sub_exp) => {
                walk_expr(cx, &**sub_exp, scope_stack, scope_map);
            }

            ast::ExprAssignOp(_, ref lhs, ref rhs) |
            ast::ExprIndex(ref lhs, ref rhs) |
            ast::ExprBinary(_, ref lhs, ref rhs)    => {
                walk_expr(cx, &**lhs, scope_stack, scope_map);
                walk_expr(cx, &**rhs, scope_stack, scope_map);
            }

            ast::ExprRange(ref start, ref end) => {
                start.as_ref().map(|e| walk_expr(cx, &**e, scope_stack, scope_map));
                end.as_ref().map(|e| walk_expr(cx, &**e, scope_stack, scope_map));
            }

            ast::ExprVec(ref init_expressions) |
            ast::ExprTup(ref init_expressions) => {
                for ie in init_expressions {
                    walk_expr(cx, &**ie, scope_stack, scope_map);
                }
            }

            ast::ExprAssign(ref sub_exp1, ref sub_exp2) |
            ast::ExprRepeat(ref sub_exp1, ref sub_exp2) => {
                walk_expr(cx, &**sub_exp1, scope_stack, scope_map);
                walk_expr(cx, &**sub_exp2, scope_stack, scope_map);
            }

            ast::ExprIf(ref cond_exp, ref then_block, ref opt_else_exp) => {
                walk_expr(cx, &**cond_exp, scope_stack, scope_map);

                with_new_scope(cx,
                               then_block.span,
                               scope_stack,
                               scope_map,
                               |cx, scope_stack, scope_map| {
                    walk_block(cx, &**then_block, scope_stack, scope_map);
                });

                match *opt_else_exp {
                    Some(ref else_exp) =>
                        walk_expr(cx, &**else_exp, scope_stack, scope_map),
                    _ => ()
                }
            }

            ast::ExprIfLet(..) => {
                cx.sess().span_bug(exp.span, "debuginfo::create_scope_map() - \
                                              Found unexpanded if-let.");
            }

            ast::ExprWhile(ref cond_exp, ref loop_body, _) => {
                walk_expr(cx, &**cond_exp, scope_stack, scope_map);

                with_new_scope(cx,
                               loop_body.span,
                               scope_stack,
                               scope_map,
                               |cx, scope_stack, scope_map| {
                    walk_block(cx, &**loop_body, scope_stack, scope_map);
                })
            }

            ast::ExprWhileLet(..) => {
                cx.sess().span_bug(exp.span, "debuginfo::create_scope_map() - \
                                              Found unexpanded while-let.");
            }

            ast::ExprForLoop(..) => {
                cx.sess().span_bug(exp.span, "debuginfo::create_scope_map() - \
                                              Found unexpanded for loop.");
            }

            ast::ExprMac(_) => {
                cx.sess().span_bug(exp.span, "debuginfo::create_scope_map() - \
                                              Found unexpanded macro.");
            }

            ast::ExprLoop(ref block, _) |
            ast::ExprBlock(ref block)   => {
                with_new_scope(cx,
                               block.span,
                               scope_stack,
                               scope_map,
                               |cx, scope_stack, scope_map| {
                    walk_block(cx, &**block, scope_stack, scope_map);
                })
            }

            ast::ExprClosure(_, ref decl, ref block) => {
                with_new_scope(cx,
                               block.span,
                               scope_stack,
                               scope_map,
                               |cx, scope_stack, scope_map| {
                    for &ast::Arg { pat: ref pattern, .. } in &decl.inputs {
                        walk_pattern(cx, &**pattern, scope_stack, scope_map);
                    }

                    walk_block(cx, &**block, scope_stack, scope_map);
                })
            }

            ast::ExprCall(ref fn_exp, ref args) => {
                walk_expr(cx, &**fn_exp, scope_stack, scope_map);

                for arg_exp in args {
                    walk_expr(cx, &**arg_exp, scope_stack, scope_map);
                }
            }

            ast::ExprMethodCall(_, _, ref args) => {
                for arg_exp in args {
                    walk_expr(cx, &**arg_exp, scope_stack, scope_map);
                }
            }

            ast::ExprMatch(ref discriminant_exp, ref arms, _) => {
                walk_expr(cx, &**discriminant_exp, scope_stack, scope_map);

                // For each arm we have to first walk the pattern as these might
                // introduce new artificial scopes. It should be sufficient to
                // walk only one pattern per arm, as they all must contain the
                // same binding names.

                for arm_ref in arms {
                    let arm_span = arm_ref.pats[0].span;

                    with_new_scope(cx,
                                   arm_span,
                                   scope_stack,
                                   scope_map,
                                   |cx, scope_stack, scope_map| {
                        for pat in &arm_ref.pats {
                            walk_pattern(cx, &**pat, scope_stack, scope_map);
                        }

                        if let Some(ref guard_exp) = arm_ref.guard {
                            walk_expr(cx, &**guard_exp, scope_stack, scope_map)
                        }

                        walk_expr(cx, &*arm_ref.body, scope_stack, scope_map);
                    })
                }
            }

            ast::ExprStruct(_, ref fields, ref base_exp) => {
                for &ast::Field { expr: ref exp, .. } in fields {
                    walk_expr(cx, &**exp, scope_stack, scope_map);
                }

                match *base_exp {
                    Some(ref exp) => walk_expr(cx, &**exp, scope_stack, scope_map),
                    None => ()
                }
            }

            ast::ExprInlineAsm(ast::InlineAsm { ref inputs,
                                                ref outputs,
                                                .. }) => {
                // inputs, outputs: Vec<(String, P<Expr>)>
                for &(_, ref exp) in inputs {
                    walk_expr(cx, &**exp, scope_stack, scope_map);
                }

                for &(_, ref exp, _) in outputs {
                    walk_expr(cx, &**exp, scope_stack, scope_map);
                }
            }
        }
    }
}


//=-----------------------------------------------------------------------------
// Type Names for Debug Info
//=-----------------------------------------------------------------------------

// Compute the name of the type as it should be stored in debuginfo. Does not do
// any caching, i.e. calling the function twice with the same type will also do
// the work twice. The `qualified` parameter only affects the first level of the
// type name, further levels (i.e. type parameters) are always fully qualified.
fn compute_debuginfo_type_name<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                                         t: Ty<'tcx>,
                                         qualified: bool)
                                         -> String {
    let mut result = String::with_capacity(64);
    push_debuginfo_type_name(cx, t, qualified, &mut result);
    result
}

// Pushes the name of the type as it should be stored in debuginfo on the
// `output` String. See also compute_debuginfo_type_name().
fn push_debuginfo_type_name<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                                      t: Ty<'tcx>,
                                      qualified: bool,
                                      output: &mut String) {
    match t.sty {
        ty::ty_bool              => output.push_str("bool"),
        ty::ty_char              => output.push_str("char"),
        ty::ty_str               => output.push_str("str"),
        ty::ty_int(ast::TyIs)     => output.push_str("isize"),
        ty::ty_int(ast::TyI8)    => output.push_str("i8"),
        ty::ty_int(ast::TyI16)   => output.push_str("i16"),
        ty::ty_int(ast::TyI32)   => output.push_str("i32"),
        ty::ty_int(ast::TyI64)   => output.push_str("i64"),
        ty::ty_uint(ast::TyUs)    => output.push_str("usize"),
        ty::ty_uint(ast::TyU8)   => output.push_str("u8"),
        ty::ty_uint(ast::TyU16)  => output.push_str("u16"),
        ty::ty_uint(ast::TyU32)  => output.push_str("u32"),
        ty::ty_uint(ast::TyU64)  => output.push_str("u64"),
        ty::ty_float(ast::TyF32) => output.push_str("f32"),
        ty::ty_float(ast::TyF64) => output.push_str("f64"),
        ty::ty_struct(def_id, substs) |
        ty::ty_enum(def_id, substs) => {
            push_item_name(cx, def_id, qualified, output);
            push_type_params(cx, substs, output);
        },
        ty::ty_tup(ref component_types) => {
            output.push('(');
            for &component_type in component_types {
                push_debuginfo_type_name(cx, component_type, true, output);
                output.push_str(", ");
            }
            if !component_types.is_empty() {
                output.pop();
                output.pop();
            }
            output.push(')');
        },
        ty::ty_uniq(inner_type) => {
            output.push_str("Box<");
            push_debuginfo_type_name(cx, inner_type, true, output);
            output.push('>');
        },
        ty::ty_ptr(ty::mt { ty: inner_type, mutbl } ) => {
            output.push('*');
            match mutbl {
                ast::MutImmutable => output.push_str("const "),
                ast::MutMutable => output.push_str("mut "),
            }

            push_debuginfo_type_name(cx, inner_type, true, output);
        },
        ty::ty_rptr(_, ty::mt { ty: inner_type, mutbl }) => {
            output.push('&');
            if mutbl == ast::MutMutable {
                output.push_str("mut ");
            }

            push_debuginfo_type_name(cx, inner_type, true, output);
        },
        ty::ty_vec(inner_type, optional_length) => {
            output.push('[');
            push_debuginfo_type_name(cx, inner_type, true, output);

            match optional_length {
                Some(len) => {
                    output.push_str(&format!("; {}", len));
                }
                None => { /* nothing to do */ }
            };

            output.push(']');
        },
        ty::ty_trait(ref trait_data) => {
            let principal = ty::erase_late_bound_regions(cx.tcx(), &trait_data.principal);
            push_item_name(cx, principal.def_id, false, output);
            push_type_params(cx, principal.substs, output);
        },
        ty::ty_bare_fn(_, &ty::BareFnTy{ unsafety, abi, ref sig } ) => {
            if unsafety == ast::Unsafety::Unsafe {
                output.push_str("unsafe ");
            }

            if abi != ::syntax::abi::Rust {
                output.push_str("extern \"");
                output.push_str(abi.name());
                output.push_str("\" ");
            }

            output.push_str("fn(");

            let sig = ty::erase_late_bound_regions(cx.tcx(), sig);
            if sig.inputs.len() > 0 {
                for &parameter_type in &sig.inputs {
                    push_debuginfo_type_name(cx, parameter_type, true, output);
                    output.push_str(", ");
                }
                output.pop();
                output.pop();
            }

            if sig.variadic {
                if sig.inputs.len() > 0 {
                    output.push_str(", ...");
                } else {
                    output.push_str("...");
                }
            }

            output.push(')');

            match sig.output {
                ty::FnConverging(result_type) if ty::type_is_nil(result_type) => {}
                ty::FnConverging(result_type) => {
                    output.push_str(" -> ");
                    push_debuginfo_type_name(cx, result_type, true, output);
                }
                ty::FnDiverging => {
                    output.push_str(" -> !");
                }
            }
        },
        ty::ty_closure(..) => {
            output.push_str("closure");
        }
        ty::ty_err |
        ty::ty_infer(_) |
        ty::ty_projection(..) |
        ty::ty_param(_) => {
            cx.sess().bug(&format!("debuginfo: Trying to create type name for \
                unexpected type: {}", ppaux::ty_to_string(cx.tcx(), t)));
        }
    }

    fn push_item_name(cx: &CrateContext,
                      def_id: ast::DefId,
                      qualified: bool,
                      output: &mut String) {
        ty::with_path(cx.tcx(), def_id, |path| {
            if qualified {
                if def_id.krate == ast::LOCAL_CRATE {
                    output.push_str(crate_root_namespace(cx));
                    output.push_str("::");
                }

                let mut path_element_count = 0;
                for path_element in path {
                    let name = token::get_name(path_element.name());
                    output.push_str(&name);
                    output.push_str("::");
                    path_element_count += 1;
                }

                if path_element_count == 0 {
                    cx.sess().bug("debuginfo: Encountered empty item path!");
                }

                output.pop();
                output.pop();
            } else {
                let name = token::get_name(path.last()
                                               .expect("debuginfo: Empty item path?")
                                               .name());
                output.push_str(&name);
            }
        });
    }

    // Pushes the type parameters in the given `Substs` to the output string.
    // This ignores region parameters, since they can't reliably be
    // reconstructed for items from non-local crates. For local crates, this
    // would be possible but with inlining and LTO we have to use the least
    // common denominator - otherwise we would run into conflicts.
    fn push_type_params<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                                  substs: &subst::Substs<'tcx>,
                                  output: &mut String) {
        if substs.types.is_empty() {
            return;
        }

        output.push('<');

        for &type_parameter in substs.types.iter() {
            push_debuginfo_type_name(cx, type_parameter, true, output);
            output.push_str(", ");
        }

        output.pop();
        output.pop();

        output.push('>');
    }
}


//=-----------------------------------------------------------------------------
// Namespace Handling
//=-----------------------------------------------------------------------------

struct NamespaceTreeNode {
    name: ast::Name,
    scope: DIScope,
    parent: Option<Weak<NamespaceTreeNode>>,
}

impl NamespaceTreeNode {
    fn mangled_name_of_contained_item(&self, item_name: &str) -> String {
        fn fill_nested(node: &NamespaceTreeNode, output: &mut String) {
            match node.parent {
                Some(ref parent) => fill_nested(&*parent.upgrade().unwrap(), output),
                None => {}
            }
            let string = token::get_name(node.name);
            output.push_str(&format!("{}", string.len()));
            output.push_str(&string);
        }

        let mut name = String::from_str("_ZN");
        fill_nested(self, &mut name);
        name.push_str(&format!("{}", item_name.len()));
        name.push_str(item_name);
        name.push('E');
        name
    }
}

fn crate_root_namespace<'a>(cx: &'a CrateContext) -> &'a str {
    &cx.link_meta().crate_name
}

fn namespace_for_item(cx: &CrateContext, def_id: ast::DefId) -> Rc<NamespaceTreeNode> {
    ty::with_path(cx.tcx(), def_id, |path| {
        // prepend crate name if not already present
        let krate = if def_id.krate == ast::LOCAL_CRATE {
            let crate_namespace_ident = token::str_to_ident(crate_root_namespace(cx));
            Some(ast_map::PathMod(crate_namespace_ident.name))
        } else {
            None
        };
        let mut path = krate.into_iter().chain(path).peekable();

        let mut current_key = Vec::new();
        let mut parent_node: Option<Rc<NamespaceTreeNode>> = None;

        // Create/Lookup namespace for each element of the path.
        loop {
            // Emulate a for loop so we can use peek below.
            let path_element = match path.next() {
                Some(e) => e,
                None => break
            };
            // Ignore the name of the item (the last path element).
            if path.peek().is_none() {
                break;
            }

            let name = path_element.name();
            current_key.push(name);

            let existing_node = debug_context(cx).namespace_map.borrow()
                                                 .get(&current_key).cloned();
            let current_node = match existing_node {
                Some(existing_node) => existing_node,
                None => {
                    // create and insert
                    let parent_scope = match parent_node {
                        Some(ref node) => node.scope,
                        None => ptr::null_mut()
                    };
                    let namespace_name = token::get_name(name);
                    let namespace_name = CString::new(namespace_name.as_bytes()).unwrap();
                    let scope = unsafe {
                        llvm::LLVMDIBuilderCreateNameSpace(
                            DIB(cx),
                            parent_scope,
                            namespace_name.as_ptr(),
                            // cannot reconstruct file ...
                            ptr::null_mut(),
                            // ... or line information, but that's not so important.
                            0)
                    };

                    let node = Rc::new(NamespaceTreeNode {
                        name: name,
                        scope: scope,
                        parent: parent_node.map(|parent| parent.downgrade()),
                    });

                    debug_context(cx).namespace_map.borrow_mut()
                                     .insert(current_key.clone(), node.clone());

                    node
                }
            };

            parent_node = Some(current_node);
        }

        match parent_node {
            Some(node) => node,
            None => {
                cx.sess().bug(&format!("debuginfo::namespace_for_item(): \
                                       path too short for {:?}",
                                      def_id));
            }
        }
    })
}


//=-----------------------------------------------------------------------------
// .debug_gdb_scripts binary section
//=-----------------------------------------------------------------------------

/// Inserts a side-effect free instruction sequence that makes sure that the
/// .debug_gdb_scripts global is referenced, so it isn't removed by the linker.
pub fn insert_reference_to_gdb_debug_scripts_section_global(ccx: &CrateContext) {
    if needs_gdb_debug_scripts_section(ccx) {
        let empty = CString::new("").unwrap();
        let gdb_debug_scripts_section_global =
            get_or_insert_gdb_debug_scripts_section_global(ccx);
        unsafe {
            let volative_load_instruction =
                llvm::LLVMBuildLoad(ccx.raw_builder(),
                                    gdb_debug_scripts_section_global,
                                    empty.as_ptr());
            llvm::LLVMSetVolatile(volative_load_instruction, llvm::True);
        }
    }
}

/// Allocates the global variable responsible for the .debug_gdb_scripts binary
/// section.
fn get_or_insert_gdb_debug_scripts_section_global(ccx: &CrateContext)
                                                  -> llvm::ValueRef {
    let section_var_name = b"__rustc_debug_gdb_scripts_section__\0";

    let section_var = unsafe {
        llvm::LLVMGetNamedGlobal(ccx.llmod(),
                                 section_var_name.as_ptr() as *const _)
    };

    if section_var == ptr::null_mut() {
        let section_name = b".debug_gdb_scripts\0";
        let section_contents = b"\x01gdb_load_rust_pretty_printers.py\0";

        unsafe {
            let llvm_type = Type::array(&Type::i8(ccx),
                                        section_contents.len() as u64);
            let section_var = llvm::LLVMAddGlobal(ccx.llmod(),
                                                  llvm_type.to_ref(),
                                                  section_var_name.as_ptr()
                                                    as *const _);
            llvm::LLVMSetSection(section_var, section_name.as_ptr() as *const _);
            llvm::LLVMSetInitializer(section_var, C_bytes(ccx, section_contents));
            llvm::LLVMSetGlobalConstant(section_var, llvm::True);
            llvm::LLVMSetUnnamedAddr(section_var, llvm::True);
            llvm::SetLinkage(section_var, llvm::Linkage::LinkOnceODRLinkage);
            // This should make sure that the whole section is not larger than
            // the string it contains. Otherwise we get a warning from GDB.
            llvm::LLVMSetAlignment(section_var, 1);
            section_var
        }
    } else {
        section_var
    }
}

fn needs_gdb_debug_scripts_section(ccx: &CrateContext) -> bool {
    let omit_gdb_pretty_printer_section =
        attr::contains_name(&ccx.tcx()
                                .map
                                .krate()
                                .attrs,
                            "omit_gdb_pretty_printer_section");

    !omit_gdb_pretty_printer_section &&
    !ccx.sess().target.target.options.is_like_osx &&
    !ccx.sess().target.target.options.is_like_windows &&
    ccx.sess().opts.debuginfo != NoDebugInfo
}
