base.rs

// Copyright 2012-2015 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.

//! Translate the completed AST to the LLVM IR.
//!
//! Some functions here, such as trans_block and trans_expr, return a value --
//! the result of the translation to LLVM -- while others, such as trans_fn
//! and trans_item, are called only for the side effect of adding a
//! particular definition to the LLVM IR output we're producing.
//!
//! Hopefully useful general knowledge about trans:
//!
//!   * There's no way to find out the Ty type of a ValueRef.  Doing so
//!     would be "trying to get the eggs out of an omelette" (credit:
//!     pcwalton).  You can, instead, find out its TypeRef by calling val_ty,
//!     but one TypeRef corresponds to many `Ty`s; for instance, tup(int, int,
//!     int) and rec(x=int, y=int, z=int) will have the same TypeRef.

#![allow(non_camel_case_types)]

pub use self::ValueOrigin::*;

use super::CrateTranslation;
use super::ModuleTranslation;

use back::{link, symbol_names};
use lint;
use llvm::{BasicBlockRef, Linkage, ValueRef, Vector, get_param};
use llvm;
use rustc::cfg;
use rustc::hir::def_id::DefId;
use rustc::infer;
use middle::lang_items::{LangItem, ExchangeMallocFnLangItem, StartFnLangItem};
use middle::weak_lang_items;
use rustc::hir::pat_util::simple_name;
use rustc::ty::subst::{self, Substs};
use rustc::traits;
use rustc::ty::{self, Ty, TyCtxt, TypeFoldable};
use rustc::ty::adjustment::CustomCoerceUnsized;
use rustc::dep_graph::DepNode;
use rustc::hir::map as hir_map;
use rustc::util::common::time;
use rustc::mir::mir_map::MirMap;
use session::config::{self, NoDebugInfo, FullDebugInfo};
use session::Session;
use _match;
use abi::{self, Abi, FnType};
use adt;
use attributes;
use build::*;
use builder::{Builder, noname};
use callee::{Callee, CallArgs, ArgExprs, ArgVals};
use cleanup::{self, CleanupMethods, DropHint};
use closure;
use common::{Block, C_bool, C_bytes_in_context, C_i32, C_int, C_uint, C_integral};
use collector::{self, TransItem, TransItemState, TransItemCollectionMode};
use common::{C_null, C_struct_in_context, C_u64, C_u8, C_undef};
use common::{CrateContext, DropFlagHintsMap, Field, FunctionContext};
use common::{Result, NodeIdAndSpan, VariantInfo};
use common::{node_id_type, fulfill_obligation};
use common::{type_is_immediate, type_is_zero_size, val_ty};
use common;
use consts;
use context::{SharedCrateContext, CrateContextList};
use controlflow;
use datum;
use debuginfo::{self, DebugLoc, ToDebugLoc};
use declare;
use expr;
use glue;
use inline;
use machine;
use machine::{llalign_of_min, llsize_of, llsize_of_real};
use meth;
use mir;
use monomorphize::{self, Instance};
use partitioning::{self, PartitioningStrategy, InstantiationMode};
use symbol_names_test;
use tvec;
use type_::Type;
use type_of;
use type_of::*;
use value::Value;
use Disr;
use util::common::indenter;
use util::sha2::Sha256;
use util::nodemap::{NodeMap, NodeSet};

use arena::TypedArena;
use libc::c_uint;
use std::ffi::{CStr, CString};
use std::cell::{Cell, RefCell};
use std::collections::{HashMap, HashSet};
use std::str;
use std::{i8, i16, i32, i64};
use syntax::codemap::{Span, DUMMY_SP};
use syntax::parse::token::InternedString;
use syntax::attr::AttrMetaMethods;
use syntax::attr;
use rustc::hir::intravisit::{self, Visitor};
use rustc::hir;
use syntax::ast;

thread_local! {
    static TASK_LOCAL_INSN_KEY: RefCell<Option<Vec<&'static str>>> = {
        RefCell::new(None)
    }
}

pub fn with_insn_ctxt<F>(blk: F)
    where F: FnOnce(&[&'static str])
{
    TASK_LOCAL_INSN_KEY.with(move |slot| {
        slot.borrow().as_ref().map(move |s| blk(s));
    })
}

pub fn init_insn_ctxt() {
    TASK_LOCAL_INSN_KEY.with(|slot| {
        *slot.borrow_mut() = Some(Vec::new());
    });
}

pub struct _InsnCtxt {
    _cannot_construct_outside_of_this_module: (),
}

impl Drop for _InsnCtxt {
    fn drop(&mut self) {
        TASK_LOCAL_INSN_KEY.with(|slot| {
            match slot.borrow_mut().as_mut() {
                Some(ctx) => {
                    ctx.pop();
                }
                None => {}
            }
        })
    }
}

pub fn push_ctxt(s: &'static str) -> _InsnCtxt {
    debug!("new InsnCtxt: {}", s);
    TASK_LOCAL_INSN_KEY.with(|slot| {
        if let Some(ctx) = slot.borrow_mut().as_mut() {
            ctx.push(s)
        }
    });
    _InsnCtxt {
        _cannot_construct_outside_of_this_module: (),
    }
}

pub struct StatRecorder<'a, 'tcx: 'a> {
    ccx: &'a CrateContext<'a, 'tcx>,
    name: Option<String>,
    istart: usize,
}

impl<'a, 'tcx> StatRecorder<'a, 'tcx> {
    pub fn new(ccx: &'a CrateContext<'a, 'tcx>, name: String) -> StatRecorder<'a, 'tcx> {
        let istart = ccx.stats().n_llvm_insns.get();
        StatRecorder {
            ccx: ccx,
            name: Some(name),
            istart: istart,
        }
    }
}

impl<'a, 'tcx> Drop for StatRecorder<'a, 'tcx> {
    fn drop(&mut self) {
        if self.ccx.sess().trans_stats() {
            let iend = self.ccx.stats().n_llvm_insns.get();
            self.ccx
                .stats()
                .fn_stats
                .borrow_mut()
                .push((self.name.take().unwrap(), iend - self.istart));
            self.ccx.stats().n_fns.set(self.ccx.stats().n_fns.get() + 1);
            // Reset LLVM insn count to avoid compound costs.
            self.ccx.stats().n_llvm_insns.set(self.istart);
        }
    }
}

pub fn kind_for_closure(ccx: &CrateContext, closure_id: DefId) -> ty::ClosureKind {
    *ccx.tcx().tables.borrow().closure_kinds.get(&closure_id).unwrap()
}

fn require_alloc_fn<'blk, 'tcx>(bcx: Block<'blk, 'tcx>, info_ty: Ty<'tcx>, it: LangItem) -> DefId {
    match bcx.tcx().lang_items.require(it) {
        Ok(id) => id,
        Err(s) => {
            bcx.sess().fatal(&format!("allocation of `{}` {}", info_ty, s));
        }
    }
}

// The following malloc_raw_dyn* functions allocate a box to contain
// a given type, but with a potentially dynamic size.

pub fn malloc_raw_dyn<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
                                  llty_ptr: Type,
                                  info_ty: Ty<'tcx>,
                                  size: ValueRef,
                                  align: ValueRef,
                                  debug_loc: DebugLoc)
                                  -> Result<'blk, 'tcx> {
    let _icx = push_ctxt("malloc_raw_exchange");

    // Allocate space:
    let def_id = require_alloc_fn(bcx, info_ty, ExchangeMallocFnLangItem);
    let r = Callee::def(bcx.ccx(), def_id, bcx.tcx().mk_substs(Substs::empty()))
        .call(bcx, debug_loc, ArgVals(&[size, align]), None);

    Result::new(r.bcx, PointerCast(r.bcx, r.val, llty_ptr))
}


pub fn bin_op_to_icmp_predicate(op: hir::BinOp_,
                                signed: bool)
                                -> llvm::IntPredicate {
    match op {
        hir::BiEq => llvm::IntEQ,
        hir::BiNe => llvm::IntNE,
        hir::BiLt => if signed { llvm::IntSLT } else { llvm::IntULT },
        hir::BiLe => if signed { llvm::IntSLE } else { llvm::IntULE },
        hir::BiGt => if signed { llvm::IntSGT } else { llvm::IntUGT },
        hir::BiGe => if signed { llvm::IntSGE } else { llvm::IntUGE },
        op => {
            bug!("comparison_op_to_icmp_predicate: expected comparison operator, \
                  found {:?}",
                 op)
        }
    }
}

pub fn bin_op_to_fcmp_predicate(op: hir::BinOp_) -> llvm::RealPredicate {
    match op {
        hir::BiEq => llvm::RealOEQ,
        hir::BiNe => llvm::RealUNE,
        hir::BiLt => llvm::RealOLT,
        hir::BiLe => llvm::RealOLE,
        hir::BiGt => llvm::RealOGT,
        hir::BiGe => llvm::RealOGE,
        op => {
            bug!("comparison_op_to_fcmp_predicate: expected comparison operator, \
                  found {:?}",
                 op);
        }
    }
}

pub fn compare_fat_ptrs<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
                                    lhs_addr: ValueRef,
                                    lhs_extra: ValueRef,
                                    rhs_addr: ValueRef,
                                    rhs_extra: ValueRef,
                                    _t: Ty<'tcx>,
                                    op: hir::BinOp_,
                                    debug_loc: DebugLoc)
                                    -> ValueRef {
    match op {
        hir::BiEq => {
            let addr_eq = ICmp(bcx, llvm::IntEQ, lhs_addr, rhs_addr, debug_loc);
            let extra_eq = ICmp(bcx, llvm::IntEQ, lhs_extra, rhs_extra, debug_loc);
            And(bcx, addr_eq, extra_eq, debug_loc)
        }
        hir::BiNe => {
            let addr_eq = ICmp(bcx, llvm::IntNE, lhs_addr, rhs_addr, debug_loc);
            let extra_eq = ICmp(bcx, llvm::IntNE, lhs_extra, rhs_extra, debug_loc);
            Or(bcx, addr_eq, extra_eq, debug_loc)
        }
        hir::BiLe | hir::BiLt | hir::BiGe | hir::BiGt => {
            // a OP b ~ a.0 STRICT(OP) b.0 | (a.0 == b.0 && a.1 OP a.1)
            let (op, strict_op) = match op {
                hir::BiLt => (llvm::IntULT, llvm::IntULT),
                hir::BiLe => (llvm::IntULE, llvm::IntULT),
                hir::BiGt => (llvm::IntUGT, llvm::IntUGT),
                hir::BiGe => (llvm::IntUGE, llvm::IntUGT),
                _ => bug!(),
            };

            let addr_eq = ICmp(bcx, llvm::IntEQ, lhs_addr, rhs_addr, debug_loc);
            let extra_op = ICmp(bcx, op, lhs_extra, rhs_extra, debug_loc);
            let addr_eq_extra_op = And(bcx, addr_eq, extra_op, debug_loc);

            let addr_strict = ICmp(bcx, strict_op, lhs_addr, rhs_addr, debug_loc);
            Or(bcx, addr_strict, addr_eq_extra_op, debug_loc)
        }
        _ => {
            bug!("unexpected fat ptr binop");
        }
    }
}

pub fn compare_scalar_types<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
                                        lhs: ValueRef,
                                        rhs: ValueRef,
                                        t: Ty<'tcx>,
                                        op: hir::BinOp_,
                                        debug_loc: DebugLoc)
                                        -> ValueRef {
    match t.sty {
        ty::TyTuple(ref tys) if tys.is_empty() => {
            // We don't need to do actual comparisons for nil.
            // () == () holds but () < () does not.
            match op {
                hir::BiEq | hir::BiLe | hir::BiGe => return C_bool(bcx.ccx(), true),
                hir::BiNe | hir::BiLt | hir::BiGt => return C_bool(bcx.ccx(), false),
                // refinements would be nice
                _ => bug!("compare_scalar_types: must be a comparison operator"),
            }
        }
        ty::TyFnDef(..) | ty::TyFnPtr(_) | ty::TyBool | ty::TyUint(_) | ty::TyChar => {
            ICmp(bcx,
                 bin_op_to_icmp_predicate(op, false),
                 lhs,
                 rhs,
                 debug_loc)
        }
        ty::TyRawPtr(mt) if common::type_is_sized(bcx.tcx(), mt.ty) => {
            ICmp(bcx,
                 bin_op_to_icmp_predicate(op, false),
                 lhs,
                 rhs,
                 debug_loc)
        }
        ty::TyRawPtr(_) => {
            let lhs_addr = Load(bcx, GEPi(bcx, lhs, &[0, abi::FAT_PTR_ADDR]));
            let lhs_extra = Load(bcx, GEPi(bcx, lhs, &[0, abi::FAT_PTR_EXTRA]));

            let rhs_addr = Load(bcx, GEPi(bcx, rhs, &[0, abi::FAT_PTR_ADDR]));
            let rhs_extra = Load(bcx, GEPi(bcx, rhs, &[0, abi::FAT_PTR_EXTRA]));
            compare_fat_ptrs(bcx,
                             lhs_addr,
                             lhs_extra,
                             rhs_addr,
                             rhs_extra,
                             t,
                             op,
                             debug_loc)
        }
        ty::TyInt(_) => {
            ICmp(bcx,
                 bin_op_to_icmp_predicate(op, true),
                 lhs,
                 rhs,
                 debug_loc)
        }
        ty::TyFloat(_) => {
            FCmp(bcx,
                 bin_op_to_fcmp_predicate(op),
                 lhs,
                 rhs,
                 debug_loc)
        }
        // Should never get here, because t is scalar.
        _ => bug!("non-scalar type passed to compare_scalar_types"),
    }
}

pub fn compare_simd_types<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
                                      lhs: ValueRef,
                                      rhs: ValueRef,
                                      t: Ty<'tcx>,
                                      ret_ty: Type,
                                      op: hir::BinOp_,
                                      debug_loc: DebugLoc)
                                      -> ValueRef {
    let signed = match t.sty {
        ty::TyFloat(_) => {
            let cmp = bin_op_to_fcmp_predicate(op);
            return SExt(bcx, FCmp(bcx, cmp, lhs, rhs, debug_loc), ret_ty);
        },
        ty::TyUint(_) => false,
        ty::TyInt(_) => true,
        _ => bug!("compare_simd_types: invalid SIMD type"),
    };

    let cmp = bin_op_to_icmp_predicate(op, signed);
    // LLVM outputs an `< size x i1 >`, so we need to perform a sign extension
    // to get the correctly sized type. This will compile to a single instruction
    // once the IR is converted to assembly if the SIMD instruction is supported
    // by the target architecture.
    SExt(bcx, ICmp(bcx, cmp, lhs, rhs, debug_loc), ret_ty)
}

// Iterates through the elements of a structural type.
pub fn iter_structural_ty<'blk, 'tcx, F>(cx: Block<'blk, 'tcx>,
                                         av: ValueRef,
                                         t: Ty<'tcx>,
                                         mut f: F)
                                         -> Block<'blk, 'tcx>
    where F: FnMut(Block<'blk, 'tcx>, ValueRef, Ty<'tcx>) -> Block<'blk, 'tcx>
{
    let _icx = push_ctxt("iter_structural_ty");

    fn iter_variant<'blk, 'tcx, F>(cx: Block<'blk, 'tcx>,
                                   repr: &adt::Repr<'tcx>,
                                   av: adt::MaybeSizedValue,
                                   variant: ty::VariantDef<'tcx>,
                                   substs: &Substs<'tcx>,
                                   f: &mut F)
                                   -> Block<'blk, 'tcx>
        where F: FnMut(Block<'blk, 'tcx>, ValueRef, Ty<'tcx>) -> Block<'blk, 'tcx>
    {
        let _icx = push_ctxt("iter_variant");
        let tcx = cx.tcx();
        let mut cx = cx;

        for (i, field) in variant.fields.iter().enumerate() {
            let arg = monomorphize::field_ty(tcx, substs, field);
            cx = f(cx,
                   adt::trans_field_ptr(cx, repr, av, Disr::from(variant.disr_val), i),
                   arg);
        }
        return cx;
    }

    let value = if common::type_is_sized(cx.tcx(), t) {
        adt::MaybeSizedValue::sized(av)
    } else {
        let data = Load(cx, expr::get_dataptr(cx, av));
        let info = Load(cx, expr::get_meta(cx, av));
        adt::MaybeSizedValue::unsized_(data, info)
    };

    let mut cx = cx;
    match t.sty {
        ty::TyStruct(..) => {
            let repr = adt::represent_type(cx.ccx(), t);
            let VariantInfo { fields, discr } = VariantInfo::from_ty(cx.tcx(), t, None);
            for (i, &Field(_, field_ty)) in fields.iter().enumerate() {
                let llfld_a = adt::trans_field_ptr(cx, &repr, value, Disr::from(discr), i);

                let val = if common::type_is_sized(cx.tcx(), field_ty) {
                    llfld_a
                } else {
                    let scratch = datum::rvalue_scratch_datum(cx, field_ty, "__fat_ptr_iter");
                    Store(cx, llfld_a, expr::get_dataptr(cx, scratch.val));
                    Store(cx, value.meta, expr::get_meta(cx, scratch.val));
                    scratch.val
                };
                cx = f(cx, val, field_ty);
            }
        }
        ty::TyClosure(_, ref substs) => {
            let repr = adt::represent_type(cx.ccx(), t);
            for (i, upvar_ty) in substs.upvar_tys.iter().enumerate() {
                let llupvar = adt::trans_field_ptr(cx, &repr, value, Disr(0), i);
                cx = f(cx, llupvar, upvar_ty);
            }
        }
        ty::TyArray(_, n) => {
            let (base, len) = tvec::get_fixed_base_and_len(cx, value.value, n);
            let unit_ty = t.sequence_element_type(cx.tcx());
            cx = tvec::iter_vec_raw(cx, base, unit_ty, len, f);
        }
        ty::TySlice(_) | ty::TyStr => {
            let unit_ty = t.sequence_element_type(cx.tcx());
            cx = tvec::iter_vec_raw(cx, value.value, unit_ty, value.meta, f);
        }
        ty::TyTuple(ref args) => {
            let repr = adt::represent_type(cx.ccx(), t);
            for (i, arg) in args.iter().enumerate() {
                let llfld_a = adt::trans_field_ptr(cx, &repr, value, Disr(0), i);
                cx = f(cx, llfld_a, *arg);
            }
        }
        ty::TyEnum(en, substs) => {
            let fcx = cx.fcx;
            let ccx = fcx.ccx;

            let repr = adt::represent_type(ccx, t);
            let n_variants = en.variants.len();

            // NB: we must hit the discriminant first so that structural
            // comparison know not to proceed when the discriminants differ.

            match adt::trans_switch(cx, &repr, av, false) {
                (_match::Single, None) => {
                    if n_variants != 0 {
                        assert!(n_variants == 1);
                        cx = iter_variant(cx, &repr, adt::MaybeSizedValue::sized(av),
                                          &en.variants[0], substs, &mut f);
                    }
                }
                (_match::Switch, Some(lldiscrim_a)) => {
                    cx = f(cx, lldiscrim_a, cx.tcx().types.isize);

                    // Create a fall-through basic block for the "else" case of
                    // the switch instruction we're about to generate. Note that
                    // we do **not** use an Unreachable instruction here, even
                    // though most of the time this basic block will never be hit.
                    //
                    // When an enum is dropped it's contents are currently
                    // overwritten to DTOR_DONE, which means the discriminant
                    // could have changed value to something not within the actual
                    // range of the discriminant. Currently this function is only
                    // used for drop glue so in this case we just return quickly
                    // from the outer function, and any other use case will only
                    // call this for an already-valid enum in which case the `ret
                    // void` will never be hit.
                    let ret_void_cx = fcx.new_temp_block("enum-iter-ret-void");
                    RetVoid(ret_void_cx, DebugLoc::None);
                    let llswitch = Switch(cx, lldiscrim_a, ret_void_cx.llbb, n_variants);
                    let next_cx = fcx.new_temp_block("enum-iter-next");

                    for variant in &en.variants {
                        let variant_cx = fcx.new_temp_block(&format!("enum-iter-variant-{}",
                                                                     &variant.disr_val
                                                                             .to_string()));
                        let case_val = adt::trans_case(cx, &repr, Disr::from(variant.disr_val));
                        AddCase(llswitch, case_val, variant_cx.llbb);
                        let variant_cx = iter_variant(variant_cx,
                                                      &repr,
                                                      value,
                                                      variant,
                                                      substs,
                                                      &mut f);
                        Br(variant_cx, next_cx.llbb, DebugLoc::None);
                    }
                    cx = next_cx;
                }
                _ => ccx.sess().unimpl("value from adt::trans_switch in iter_structural_ty"),
            }
        }
        _ => {
            cx.sess().unimpl(&format!("type in iter_structural_ty: {}", t))
        }
    }
    return cx;
}


/// Retrieve the information we are losing (making dynamic) in an unsizing
/// adjustment.
///
/// The `old_info` argument is a bit funny. It is intended for use
/// in an upcast, where the new vtable for an object will be drived
/// from the old one.
pub fn unsized_info<'ccx, 'tcx>(ccx: &CrateContext<'ccx, 'tcx>,
                                source: Ty<'tcx>,
                                target: Ty<'tcx>,
                                old_info: Option<ValueRef>)
                                -> ValueRef {
    let (source, target) = ccx.tcx().struct_lockstep_tails(source, target);
    match (&source.sty, &target.sty) {
        (&ty::TyArray(_, len), &ty::TySlice(_)) => C_uint(ccx, len),
        (&ty::TyTrait(_), &ty::TyTrait(_)) => {
            // For now, upcasts are limited to changes in marker
            // traits, and hence never actually require an actual
            // change to the vtable.
            old_info.expect("unsized_info: missing old info for trait upcast")
        }
        (_, &ty::TyTrait(box ty::TraitTy { ref principal, .. })) => {
            // Note that we preserve binding levels here:
            let substs = principal.0.substs.with_self_ty(source).erase_regions();
            let substs = ccx.tcx().mk_substs(substs);
            let trait_ref = ty::Binder(ty::TraitRef {
                def_id: principal.def_id(),
                substs: substs,
            });
            consts::ptrcast(meth::get_vtable(ccx, trait_ref),
                            Type::vtable_ptr(ccx))
        }
        _ => bug!("unsized_info: invalid unsizing {:?} -> {:?}",
                                     source,
                                     target),
    }
}

/// Coerce `src` to `dst_ty`. `src_ty` must be a thin pointer.
pub fn unsize_thin_ptr<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
                                   src: ValueRef,
                                   src_ty: Ty<'tcx>,
                                   dst_ty: Ty<'tcx>)
                                   -> (ValueRef, ValueRef) {
    debug!("unsize_thin_ptr: {:?} => {:?}", src_ty, dst_ty);
    match (&src_ty.sty, &dst_ty.sty) {
        (&ty::TyBox(a), &ty::TyBox(b)) |
        (&ty::TyRef(_, ty::TypeAndMut { ty: a, .. }),
         &ty::TyRef(_, ty::TypeAndMut { ty: b, .. })) |
        (&ty::TyRef(_, ty::TypeAndMut { ty: a, .. }),
         &ty::TyRawPtr(ty::TypeAndMut { ty: b, .. })) |
        (&ty::TyRawPtr(ty::TypeAndMut { ty: a, .. }),
         &ty::TyRawPtr(ty::TypeAndMut { ty: b, .. })) => {
            assert!(common::type_is_sized(bcx.tcx(), a));
            let ptr_ty = type_of::in_memory_type_of(bcx.ccx(), b).ptr_to();
            (PointerCast(bcx, src, ptr_ty),
             unsized_info(bcx.ccx(), a, b, None))
        }
        _ => bug!("unsize_thin_ptr: called on bad types"),
    }
}

/// Coerce `src`, which is a reference to a value of type `src_ty`,
/// to a value of type `dst_ty` and store the result in `dst`
pub fn coerce_unsized_into<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
                                       src: ValueRef,
                                       src_ty: Ty<'tcx>,
                                       dst: ValueRef,
                                       dst_ty: Ty<'tcx>) {
    match (&src_ty.sty, &dst_ty.sty) {
        (&ty::TyBox(..), &ty::TyBox(..)) |
        (&ty::TyRef(..), &ty::TyRef(..)) |
        (&ty::TyRef(..), &ty::TyRawPtr(..)) |
        (&ty::TyRawPtr(..), &ty::TyRawPtr(..)) => {
            let (base, info) = if common::type_is_fat_ptr(bcx.tcx(), src_ty) {
                // fat-ptr to fat-ptr unsize preserves the vtable
                load_fat_ptr(bcx, src, src_ty)
            } else {
                let base = load_ty(bcx, src, src_ty);
                unsize_thin_ptr(bcx, base, src_ty, dst_ty)
            };
            store_fat_ptr(bcx, base, info, dst, dst_ty);
        }

        // This can be extended to enums and tuples in the future.
        // (&ty::TyEnum(def_id_a, _), &ty::TyEnum(def_id_b, _)) |
        (&ty::TyStruct(def_a, _), &ty::TyStruct(def_b, _)) => {
            assert_eq!(def_a, def_b);

            let src_repr = adt::represent_type(bcx.ccx(), src_ty);
            let src_fields = match &*src_repr {
                &adt::Repr::Univariant(ref s, _) => &s.fields,
                _ => bug!("struct has non-univariant repr"),
            };
            let dst_repr = adt::represent_type(bcx.ccx(), dst_ty);
            let dst_fields = match &*dst_repr {
                &adt::Repr::Univariant(ref s, _) => &s.fields,
                _ => bug!("struct has non-univariant repr"),
            };

            let src = adt::MaybeSizedValue::sized(src);
            let dst = adt::MaybeSizedValue::sized(dst);

            let iter = src_fields.iter().zip(dst_fields).enumerate();
            for (i, (src_fty, dst_fty)) in iter {
                if type_is_zero_size(bcx.ccx(), dst_fty) {
                    continue;
                }

                let src_f = adt::trans_field_ptr(bcx, &src_repr, src, Disr(0), i);
                let dst_f = adt::trans_field_ptr(bcx, &dst_repr, dst, Disr(0), i);
                if src_fty == dst_fty {
                    memcpy_ty(bcx, dst_f, src_f, src_fty);
                } else {
                    coerce_unsized_into(bcx, src_f, src_fty, dst_f, dst_fty);
                }
            }
        }
        _ => bug!("coerce_unsized_into: invalid coercion {:?} -> {:?}",
                  src_ty,
                  dst_ty),
    }
}

pub fn custom_coerce_unsize_info<'ccx, 'tcx>(ccx: &SharedCrateContext<'ccx, 'tcx>,
                                             source_ty: Ty<'tcx>,
                                             target_ty: Ty<'tcx>)
                                             -> CustomCoerceUnsized {
    let trait_substs = Substs::new(subst::VecPerParamSpace::new(vec![target_ty],
                                                                vec![source_ty],
                                                                Vec::new()),
                                   subst::VecPerParamSpace::empty());

    let trait_ref = ty::Binder(ty::TraitRef {
        def_id: ccx.tcx().lang_items.coerce_unsized_trait().unwrap(),
        substs: ccx.tcx().mk_substs(trait_substs)
    });

    match fulfill_obligation(ccx, DUMMY_SP, trait_ref) {
        traits::VtableImpl(traits::VtableImplData { impl_def_id, .. }) => {
            ccx.tcx().custom_coerce_unsized_kind(impl_def_id)
        }
        vtable => {
            bug!("invalid CoerceUnsized vtable: {:?}", vtable);
        }
    }
}

pub fn cast_shift_expr_rhs(cx: Block, op: hir::BinOp_, lhs: ValueRef, rhs: ValueRef) -> ValueRef {
    cast_shift_rhs(op, lhs, rhs, |a, b| Trunc(cx, a, b), |a, b| ZExt(cx, a, b))
}

pub fn cast_shift_const_rhs(op: hir::BinOp_, lhs: ValueRef, rhs: ValueRef) -> ValueRef {
    cast_shift_rhs(op,
                   lhs,
                   rhs,
                   |a, b| unsafe { llvm::LLVMConstTrunc(a, b.to_ref()) },
                   |a, b| unsafe { llvm::LLVMConstZExt(a, b.to_ref()) })
}

fn cast_shift_rhs<F, G>(op: hir::BinOp_,
                        lhs: ValueRef,
                        rhs: ValueRef,
                        trunc: F,
                        zext: G)
                        -> ValueRef
    where F: FnOnce(ValueRef, Type) -> ValueRef,
          G: FnOnce(ValueRef, Type) -> ValueRef
{
    // Shifts may have any size int on the rhs
    if op.is_shift() {
        let mut rhs_llty = val_ty(rhs);
        let mut lhs_llty = val_ty(lhs);
        if rhs_llty.kind() == Vector {
            rhs_llty = rhs_llty.element_type()
        }
        if lhs_llty.kind() == Vector {
            lhs_llty = lhs_llty.element_type()
        }
        let rhs_sz = rhs_llty.int_width();
        let lhs_sz = lhs_llty.int_width();
        if lhs_sz < rhs_sz {
            trunc(rhs, lhs_llty)
        } else if lhs_sz > rhs_sz {
            // FIXME (#1877: If shifting by negative
            // values becomes not undefined then this is wrong.
            zext(rhs, lhs_llty)
        } else {
            rhs
        }
    } else {
        rhs
    }
}

pub fn llty_and_min_for_signed_ty<'blk, 'tcx>(cx: Block<'blk, 'tcx>,
                                              val_t: Ty<'tcx>)
                                              -> (Type, u64) {
    match val_t.sty {
        ty::TyInt(t) => {
            let llty = Type::int_from_ty(cx.ccx(), t);
            let min = match t {
                ast::IntTy::Is if llty == Type::i32(cx.ccx()) => i32::MIN as u64,
                ast::IntTy::Is => i64::MIN as u64,
                ast::IntTy::I8 => i8::MIN as u64,
                ast::IntTy::I16 => i16::MIN as u64,
                ast::IntTy::I32 => i32::MIN as u64,
                ast::IntTy::I64 => i64::MIN as u64,
            };
            (llty, min)
        }
        _ => bug!(),
    }
}

pub fn fail_if_zero_or_overflows<'blk, 'tcx>(cx: Block<'blk, 'tcx>,
                                             call_info: NodeIdAndSpan,
                                             divrem: hir::BinOp,
                                             lhs: ValueRef,
                                             rhs: ValueRef,
                                             rhs_t: Ty<'tcx>)
                                             -> Block<'blk, 'tcx> {
    let (zero_text, overflow_text) = if divrem.node == hir::BiDiv {
        ("attempted to divide by zero",
         "attempted to divide with overflow")
    } else {
        ("attempted remainder with a divisor of zero",
         "attempted remainder with overflow")
    };
    let debug_loc = call_info.debug_loc();

    let (is_zero, is_signed) = match rhs_t.sty {
        ty::TyInt(t) => {
            let zero = C_integral(Type::int_from_ty(cx.ccx(), t), 0, false);
            (ICmp(cx, llvm::IntEQ, rhs, zero, debug_loc), true)
        }
        ty::TyUint(t) => {
            let zero = C_integral(Type::uint_from_ty(cx.ccx(), t), 0, false);
            (ICmp(cx, llvm::IntEQ, rhs, zero, debug_loc), false)
        }
        ty::TyStruct(def, _) if def.is_simd() => {
            let mut res = C_bool(cx.ccx(), false);
            for i in 0..rhs_t.simd_size(cx.tcx()) {
                res = Or(cx,
                         res,
                         IsNull(cx, ExtractElement(cx, rhs, C_int(cx.ccx(), i as i64))),
                         debug_loc);
            }
            (res, false)
        }
        _ => {
            bug!("fail-if-zero on unexpected type: {}", rhs_t);
        }
    };
    let bcx = with_cond(cx, is_zero, |bcx| {
        controlflow::trans_fail(bcx, call_info, InternedString::new(zero_text))
    });

    // To quote LLVM's documentation for the sdiv instruction:
    //
    //      Division by zero leads to undefined behavior. Overflow also leads
    //      to undefined behavior; this is a rare case, but can occur, for
    //      example, by doing a 32-bit division of -2147483648 by -1.
    //
    // In order to avoid undefined behavior, we perform runtime checks for
    // signed division/remainder which would trigger overflow. For unsigned
    // integers, no action beyond checking for zero need be taken.
    if is_signed {
        let (llty, min) = llty_and_min_for_signed_ty(cx, rhs_t);
        let minus_one = ICmp(bcx,
                             llvm::IntEQ,
                             rhs,
                             C_integral(llty, !0, false),
                             debug_loc);
        with_cond(bcx, minus_one, |bcx| {
            let is_min = ICmp(bcx,
                              llvm::IntEQ,
                              lhs,
                              C_integral(llty, min, true),
                              debug_loc);
            with_cond(bcx, is_min, |bcx| {
                controlflow::trans_fail(bcx, call_info, InternedString::new(overflow_text))
            })
        })
    } else {
        bcx
    }
}

pub fn invoke<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
                          llfn: ValueRef,
                          llargs: &[ValueRef],
                          debug_loc: DebugLoc)
                          -> (ValueRef, Block<'blk, 'tcx>) {
    let _icx = push_ctxt("invoke_");
    if bcx.unreachable.get() {
        return (C_null(Type::i8(bcx.ccx())), bcx);
    }

    match bcx.opt_node_id {
        None => {
            debug!("invoke at ???");
        }
        Some(id) => {
            debug!("invoke at {}", bcx.tcx().map.node_to_string(id));
        }
    }

    if need_invoke(bcx) {
        debug!("invoking {:?} at {:?}", Value(llfn), bcx.llbb);
        for &llarg in llargs {
            debug!("arg: {:?}", Value(llarg));
        }
        let normal_bcx = bcx.fcx.new_temp_block("normal-return");
        let landing_pad = bcx.fcx.get_landing_pad();

        let llresult = Invoke(bcx,
                              llfn,
                              &llargs[..],
                              normal_bcx.llbb,
                              landing_pad,
                              debug_loc);
        return (llresult, normal_bcx);
    } else {
        debug!("calling {:?} at {:?}", Value(llfn), bcx.llbb);
        for &llarg in llargs {
            debug!("arg: {:?}", Value(llarg));
        }

        let llresult = Call(bcx, llfn, &llargs[..], debug_loc);
        return (llresult, bcx);
    }
}

/// Returns whether this session's target will use SEH-based unwinding.
///
/// This is only true for MSVC targets, and even then the 64-bit MSVC target
/// currently uses SEH-ish unwinding with DWARF info tables to the side (same as
/// 64-bit MinGW) instead of "full SEH".
pub fn wants_msvc_seh(sess: &Session) -> bool {
    sess.target.target.options.is_like_msvc
}

pub fn avoid_invoke(bcx: Block) -> bool {
    bcx.sess().no_landing_pads() || bcx.lpad().is_some()
}

pub fn need_invoke(bcx: Block) -> bool {
    if avoid_invoke(bcx) {
        false
    } else {
        bcx.fcx.needs_invoke()
    }
}

pub fn load_if_immediate<'blk, 'tcx>(cx: Block<'blk, 'tcx>, v: ValueRef, t: Ty<'tcx>) -> ValueRef {
    let _icx = push_ctxt("load_if_immediate");
    if type_is_immediate(cx.ccx(), t) {
        return load_ty(cx, v, t);
    }
    return v;
}

/// Helper for loading values from memory. Does the necessary conversion if the in-memory type
/// differs from the type used for SSA values. Also handles various special cases where the type
/// gives us better information about what we are loading.
pub fn load_ty<'blk, 'tcx>(cx: Block<'blk, 'tcx>, ptr: ValueRef, t: Ty<'tcx>) -> ValueRef {
    if cx.unreachable.get() {
        return C_undef(type_of::type_of(cx.ccx(), t));
    }
    load_ty_builder(&B(cx), ptr, t)
}

pub fn load_ty_builder<'a, 'tcx>(b: &Builder<'a, 'tcx>, ptr: ValueRef, t: Ty<'tcx>) -> ValueRef {
    let ccx = b.ccx;
    if type_is_zero_size(ccx, t) {
        return C_undef(type_of::type_of(ccx, t));
    }

    unsafe {
        let global = llvm::LLVMIsAGlobalVariable(ptr);
        if !global.is_null() && llvm::LLVMIsGlobalConstant(global) == llvm::True {
            let val = llvm::LLVMGetInitializer(global);
            if !val.is_null() {
                if t.is_bool() {
                    return llvm::LLVMConstTrunc(val, Type::i1(ccx).to_ref());
                }
                return val;
            }
        }
    }

    if t.is_bool() {
        b.trunc(b.load_range_assert(ptr, 0, 2, llvm::False), Type::i1(ccx))
    } else if t.is_char() {
        // a char is a Unicode codepoint, and so takes values from 0
        // to 0x10FFFF inclusive only.
        b.load_range_assert(ptr, 0, 0x10FFFF + 1, llvm::False)
    } else if (t.is_region_ptr() || t.is_unique()) &&
              !common::type_is_fat_ptr(ccx.tcx(), t) {
        b.load_nonnull(ptr)
    } else {
        b.load(ptr)
    }
}

/// Helper for storing values in memory. Does the necessary conversion if the in-memory type
/// differs from the type used for SSA values.
pub fn store_ty<'blk, 'tcx>(cx: Block<'blk, 'tcx>, v: ValueRef, dst: ValueRef, t: Ty<'tcx>) {
    if cx.unreachable.get() {
        return;
    }

    debug!("store_ty: {:?} : {:?} <- {:?}", Value(dst), t, Value(v));

    if common::type_is_fat_ptr(cx.tcx(), t) {
        Store(cx,
              ExtractValue(cx, v, abi::FAT_PTR_ADDR),
              expr::get_dataptr(cx, dst));
        Store(cx,
              ExtractValue(cx, v, abi::FAT_PTR_EXTRA),
              expr::get_meta(cx, dst));
    } else {
        Store(cx, from_immediate(cx, v), dst);
    }
}

pub fn store_fat_ptr<'blk, 'tcx>(cx: Block<'blk, 'tcx>,
                                 data: ValueRef,
                                 extra: ValueRef,
                                 dst: ValueRef,
                                 _ty: Ty<'tcx>) {
    // FIXME: emit metadata
    Store(cx, data, expr::get_dataptr(cx, dst));
    Store(cx, extra, expr::get_meta(cx, dst));
}

pub fn load_fat_ptr<'blk, 'tcx>(cx: Block<'blk, 'tcx>,
                                src: ValueRef,
                                _ty: Ty<'tcx>)
                                -> (ValueRef, ValueRef) {
    // FIXME: emit metadata
    (Load(cx, expr::get_dataptr(cx, src)),
     Load(cx, expr::get_meta(cx, src)))
}

pub fn from_immediate(bcx: Block, val: ValueRef) -> ValueRef {
    if val_ty(val) == Type::i1(bcx.ccx()) {
        ZExt(bcx, val, Type::i8(bcx.ccx()))
    } else {
        val
    }
}

pub fn to_immediate(bcx: Block, val: ValueRef, ty: Ty) -> ValueRef {
    if ty.is_bool() {
        Trunc(bcx, val, Type::i1(bcx.ccx()))
    } else {
        val
    }
}

pub fn init_local<'blk, 'tcx>(bcx: Block<'blk, 'tcx>, local: &hir::Local) -> Block<'blk, 'tcx> {
    debug!("init_local(bcx={}, local.id={})", bcx.to_str(), local.id);
    let _indenter = indenter();
    let _icx = push_ctxt("init_local");
    _match::store_local(bcx, local)
}

pub fn raw_block<'blk, 'tcx>(fcx: &'blk FunctionContext<'blk, 'tcx>,
                             llbb: BasicBlockRef)
                             -> Block<'blk, 'tcx> {
    common::BlockS::new(llbb, None, fcx)
}

pub fn with_cond<'blk, 'tcx, F>(bcx: Block<'blk, 'tcx>, val: ValueRef, f: F) -> Block<'blk, 'tcx>
    where F: FnOnce(Block<'blk, 'tcx>) -> Block<'blk, 'tcx>
{
    let _icx = push_ctxt("with_cond");

    if bcx.unreachable.get() || common::const_to_opt_uint(val) == Some(0) {
        return bcx;
    }

    let fcx = bcx.fcx;
    let next_cx = fcx.new_temp_block("next");
    let cond_cx = fcx.new_temp_block("cond");
    CondBr(bcx, val, cond_cx.llbb, next_cx.llbb, DebugLoc::None);
    let after_cx = f(cond_cx);
    if !after_cx.terminated.get() {
        Br(after_cx, next_cx.llbb, DebugLoc::None);
    }
    next_cx
}

enum Lifetime { Start, End }

// If LLVM lifetime intrinsic support is enabled (i.e. optimizations
// on), and `ptr` is nonzero-sized, then extracts the size of `ptr`
// and the intrinsic for `lt` and passes them to `emit`, which is in
// charge of generating code to call the passed intrinsic on whatever
// block of generated code is targetted for the intrinsic.
//
// If LLVM lifetime intrinsic support is disabled (i.e.  optimizations
// off) or `ptr` is zero-sized, then no-op (does not call `emit`).
fn core_lifetime_emit<'blk, 'tcx, F>(ccx: &'blk CrateContext<'blk, 'tcx>,
                                     ptr: ValueRef,
                                     lt: Lifetime,
                                     emit: F)
    where F: FnOnce(&'blk CrateContext<'blk, 'tcx>, machine::llsize, ValueRef)
{
    if ccx.sess().opts.optimize == config::OptLevel::No {
        return;
    }

    let _icx = push_ctxt(match lt {
        Lifetime::Start => "lifetime_start",
        Lifetime::End => "lifetime_end"
    });

    let size = machine::llsize_of_alloc(ccx, val_ty(ptr).element_type());
    if size == 0 {
        return;
    }

    let lifetime_intrinsic = ccx.get_intrinsic(match lt {
        Lifetime::Start => "llvm.lifetime.start",
        Lifetime::End => "llvm.lifetime.end"
    });
    emit(ccx, size, lifetime_intrinsic)
}

pub fn call_lifetime_start(cx: Block, ptr: ValueRef) {
    core_lifetime_emit(cx.ccx(), ptr, Lifetime::Start, |ccx, size, lifetime_start| {
        let ptr = PointerCast(cx, ptr, Type::i8p(ccx));
        Call(cx,
             lifetime_start,
             &[C_u64(ccx, size), ptr],
             DebugLoc::None);
    })
}

pub fn call_lifetime_end(cx: Block, ptr: ValueRef) {
    core_lifetime_emit(cx.ccx(), ptr, Lifetime::End, |ccx, size, lifetime_end| {
        let ptr = PointerCast(cx, ptr, Type::i8p(ccx));
        Call(cx,
             lifetime_end,
             &[C_u64(ccx, size), ptr],
             DebugLoc::None);
    })
}

// Generates code for resumption of unwind at the end of a landing pad.
pub fn trans_unwind_resume(bcx: Block, lpval: ValueRef) {
    if !bcx.sess().target.target.options.custom_unwind_resume {
        Resume(bcx, lpval);
    } else {
        let exc_ptr = ExtractValue(bcx, lpval, 0);
        bcx.fcx.eh_unwind_resume()
            .call(bcx, DebugLoc::None, ArgVals(&[exc_ptr]), None);
    }
}

pub fn call_memcpy<'bcx, 'tcx>(b: &Builder<'bcx, 'tcx>,
                               dst: ValueRef,
                               src: ValueRef,
                               n_bytes: ValueRef,
                               align: u32) {
    let _icx = push_ctxt("call_memcpy");
    let ccx = b.ccx;
    let ptr_width = &ccx.sess().target.target.target_pointer_width[..];
    let key = format!("llvm.memcpy.p0i8.p0i8.i{}", ptr_width);
    let memcpy = ccx.get_intrinsic(&key);
    let src_ptr = b.pointercast(src, Type::i8p(ccx));
    let dst_ptr = b.pointercast(dst, Type::i8p(ccx));
    let size = b.intcast(n_bytes, ccx.int_type());
    let align = C_i32(ccx, align as i32);
    let volatile = C_bool(ccx, false);
    b.call(memcpy, &[dst_ptr, src_ptr, size, align, volatile], None);
}

pub fn memcpy_ty<'blk, 'tcx>(bcx: Block<'blk, 'tcx>, dst: ValueRef, src: ValueRef, t: Ty<'tcx>) {
    let _icx = push_ctxt("memcpy_ty");
    let ccx = bcx.ccx();

    if type_is_zero_size(ccx, t) || bcx.unreachable.get() {
        return;
    }

    if t.is_structural() {
        let llty = type_of::type_of(ccx, t);
        let llsz = llsize_of(ccx, llty);
        let llalign = type_of::align_of(ccx, t);
        call_memcpy(&B(bcx), dst, src, llsz, llalign as u32);
    } else if common::type_is_fat_ptr(bcx.tcx(), t) {
        let (data, extra) = load_fat_ptr(bcx, src, t);
        store_fat_ptr(bcx, data, extra, dst, t);
    } else {
        store_ty(bcx, load_ty(bcx, src, t), dst, t);
    }
}

pub fn drop_done_fill_mem<'blk, 'tcx>(cx: Block<'blk, 'tcx>, llptr: ValueRef, t: Ty<'tcx>) {
    if cx.unreachable.get() {
        return;
    }
    let _icx = push_ctxt("drop_done_fill_mem");
    let bcx = cx;
    memfill(&B(bcx), llptr, t, adt::DTOR_DONE);
}

pub fn init_zero_mem<'blk, 'tcx>(cx: Block<'blk, 'tcx>, llptr: ValueRef, t: Ty<'tcx>) {
    if cx.unreachable.get() {
        return;
    }
    let _icx = push_ctxt("init_zero_mem");
    let bcx = cx;
    memfill(&B(bcx), llptr, t, 0);
}

// Always use this function instead of storing a constant byte to the memory
// in question. e.g. if you store a zero constant, LLVM will drown in vreg
// allocation for large data structures, and the generated code will be
// awful. (A telltale sign of this is large quantities of
// `mov [byte ptr foo],0` in the generated code.)
fn memfill<'a, 'tcx>(b: &Builder<'a, 'tcx>, llptr: ValueRef, ty: Ty<'tcx>, byte: u8) {
    let _icx = push_ctxt("memfill");
    let ccx = b.ccx;
    let llty = type_of::type_of(ccx, ty);
    let llptr = b.pointercast(llptr, Type::i8(ccx).ptr_to());
    let llzeroval = C_u8(ccx, byte);
    let size = machine::llsize_of(ccx, llty);
    let align = C_i32(ccx, type_of::align_of(ccx, ty) as i32);
    call_memset(b, llptr, llzeroval, size, align, false);
}

pub fn call_memset<'bcx, 'tcx>(b: &Builder<'bcx, 'tcx>,
                               ptr: ValueRef,
                               fill_byte: ValueRef,
                               size: ValueRef,
                               align: ValueRef,
                               volatile: bool) {
    let ccx = b.ccx;
    let ptr_width = &ccx.sess().target.target.target_pointer_width[..];
    let intrinsic_key = format!("llvm.memset.p0i8.i{}", ptr_width);
    let llintrinsicfn = ccx.get_intrinsic(&intrinsic_key);
    let volatile = C_bool(ccx, volatile);
    b.call(llintrinsicfn, &[ptr, fill_byte, size, align, volatile], None);
}


/// In general, when we create an scratch value in an alloca, the
/// creator may not know if the block (that initializes the scratch
/// with the desired value) actually dominates the cleanup associated
/// with the scratch value.
///
/// To deal with this, when we do an alloca (at the *start* of whole
/// function body), we optionally can also set the associated
/// dropped-flag state of the alloca to "dropped."
#[derive(Copy, Clone, Debug)]
pub enum InitAlloca {
    /// Indicates that the state should have its associated drop flag
    /// set to "dropped" at the point of allocation.
    Dropped,
    /// Indicates the value of the associated drop flag is irrelevant.
    /// The embedded string literal is a programmer provided argument
    /// for why. This is a safeguard forcing compiler devs to
    /// document; it might be a good idea to also emit this as a
    /// comment with the alloca itself when emitting LLVM output.ll.
    Uninit(&'static str),
}


pub fn alloc_ty<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
                            t: Ty<'tcx>,
                            name: &str) -> ValueRef {
    // pnkfelix: I do not know why alloc_ty meets the assumptions for
    // passing Uninit, but it was never needed (even back when we had
    // the original boolean `zero` flag on `lvalue_scratch_datum`).
    alloc_ty_init(bcx, t, InitAlloca::Uninit("all alloc_ty are uninit"), name)
}

/// This variant of `fn alloc_ty` does not necessarily assume that the
/// alloca should be created with no initial value. Instead the caller
/// controls that assumption via the `init` flag.
///
/// Note that if the alloca *is* initialized via `init`, then we will
/// also inject an `llvm.lifetime.start` before that initialization
/// occurs, and thus callers should not call_lifetime_start
/// themselves.  But if `init` says "uninitialized", then callers are
/// in charge of choosing where to call_lifetime_start and
/// subsequently populate the alloca.
///
/// (See related discussion on PR #30823.)
pub fn alloc_ty_init<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
                             t: Ty<'tcx>,
                             init: InitAlloca,
                             name: &str) -> ValueRef {
    let _icx = push_ctxt("alloc_ty");
    let ccx = bcx.ccx();
    let ty = type_of::type_of(ccx, t);
    assert!(!t.has_param_types());
    match init {
        InitAlloca::Dropped => alloca_dropped(bcx, t, name),
        InitAlloca::Uninit(_) => alloca(bcx, ty, name),
    }
}

pub fn alloca_dropped<'blk, 'tcx>(cx: Block<'blk, 'tcx>, ty: Ty<'tcx>, name: &str) -> ValueRef {
    let _icx = push_ctxt("alloca_dropped");
    let llty = type_of::type_of(cx.ccx(), ty);
    if cx.unreachable.get() {
        unsafe { return llvm::LLVMGetUndef(llty.ptr_to().to_ref()); }
    }
    let p = alloca(cx, llty, name);
    let b = cx.fcx.ccx.builder();
    b.position_before(cx.fcx.alloca_insert_pt.get().unwrap());

    // This is just like `call_lifetime_start` (but latter expects a
    // Block, which we do not have for `alloca_insert_pt`).
    core_lifetime_emit(cx.ccx(), p, Lifetime::Start, |ccx, size, lifetime_start| {
        let ptr = b.pointercast(p, Type::i8p(ccx));
        b.call(lifetime_start, &[C_u64(ccx, size), ptr], None);
    });
    memfill(&b, p, ty, adt::DTOR_DONE);
    p
}

pub fn alloca(cx: Block, ty: Type, name: &str) -> ValueRef {
    let _icx = push_ctxt("alloca");
    if cx.unreachable.get() {
        unsafe {
            return llvm::LLVMGetUndef(ty.ptr_to().to_ref());
        }
    }
    DebugLoc::None.apply(cx.fcx);
    Alloca(cx, ty, name)
}

pub fn set_value_name(val: ValueRef, name: &str) {
    unsafe {
        let name = CString::new(name).unwrap();
        llvm::LLVMSetValueName(val, name.as_ptr());
    }
}

struct FindNestedReturn {
    found: bool,
}

impl FindNestedReturn {
    fn new() -> FindNestedReturn {
        FindNestedReturn {
            found: false,
        }
    }
}

impl<'v> Visitor<'v> for FindNestedReturn {
    fn visit_expr(&mut self, e: &hir::Expr) {
        match e.node {
            hir::ExprRet(..) => {
                self.found = true;
            }
            _ => intravisit::walk_expr(self, e),
        }
    }
}

fn build_cfg(tcx: &TyCtxt, id: ast::NodeId) -> (ast::NodeId, Option<cfg::CFG>) {
    let blk = match tcx.map.find(id) {
        Some(hir_map::NodeItem(i)) => {
            match i.node {
                hir::ItemFn(_, _, _, _, _, ref blk) => {
                    blk
                }
                _ => bug!("unexpected item variant in has_nested_returns"),
            }
        }
        Some(hir_map::NodeTraitItem(trait_item)) => {
            match trait_item.node {
                hir::MethodTraitItem(_, Some(ref body)) => body,
                _ => {
                    bug!("unexpected variant: trait item other than a provided method in \
                          has_nested_returns")
                }
            }
        }
        Some(hir_map::NodeImplItem(impl_item)) => {
            match impl_item.node {
                hir::ImplItemKind::Method(_, ref body) => body,
                _ => {
                    bug!("unexpected variant: non-method impl item in has_nested_returns")
                }
            }
        }
        Some(hir_map::NodeExpr(e)) => {
            match e.node {
                hir::ExprClosure(_, _, ref blk, _) => blk,
                _ => bug!("unexpected expr variant in has_nested_returns"),
            }
        }
        Some(hir_map::NodeVariant(..)) |
        Some(hir_map::NodeStructCtor(..)) => return (ast::DUMMY_NODE_ID, None),

        // glue, shims, etc
        None if id == ast::DUMMY_NODE_ID => return (ast::DUMMY_NODE_ID, None),

        _ => bug!("unexpected variant in has_nested_returns: {}",
                  tcx.node_path_str(id)),
    };

    (blk.id, Some(cfg::CFG::new(tcx, blk)))
}

// Checks for the presence of "nested returns" in a function.
// Nested returns are when the inner expression of a return expression
// (the 'expr' in 'return expr') contains a return expression. Only cases
// where the outer return is actually reachable are considered. Implicit
// returns from the end of blocks are considered as well.
//
// This check is needed to handle the case where the inner expression is
// part of a larger expression that may have already partially-filled the
// return slot alloca. This can cause errors related to clean-up due to
// the clobbering of the existing value in the return slot.
fn has_nested_returns(tcx: &TyCtxt, cfg: &cfg::CFG, blk_id: ast::NodeId) -> bool {
    for index in cfg.graph.depth_traverse(cfg.entry) {
        let n = cfg.graph.node_data(index);
        match tcx.map.find(n.id()) {
            Some(hir_map::NodeExpr(ex)) => {
                if let hir::ExprRet(Some(ref ret_expr)) = ex.node {
                    let mut visitor = FindNestedReturn::new();
                    intravisit::walk_expr(&mut visitor, &ret_expr);
                    if visitor.found {
                        return true;
                    }
                }
            }
            Some(hir_map::NodeBlock(blk)) if blk.id == blk_id => {
                let mut visitor = FindNestedReturn::new();
                walk_list!(&mut visitor, visit_expr, &blk.expr);
                if visitor.found {
                    return true;
                }
            }
            _ => {}
        }
    }

    return false;
}

impl<'blk, 'tcx> FunctionContext<'blk, 'tcx> {
    /// Create a function context for the given function.
    /// Beware that you must call `fcx.init` or `fcx.bind_args`
    /// before doing anything with the returned function context.
    pub fn new(ccx: &'blk CrateContext<'blk, 'tcx>,
               llfndecl: ValueRef,
               fn_ty: FnType,
               definition: Option<(Instance<'tcx>, &ty::FnSig<'tcx>, Abi)>,
               block_arena: &'blk TypedArena<common::BlockS<'blk, 'tcx>>)
               -> FunctionContext<'blk, 'tcx> {
        let (param_substs, def_id) = match definition {
            Some((instance, _, _)) => {
                common::validate_substs(instance.substs);
                (instance.substs, Some(instance.def))
            }
            None => (ccx.tcx().mk_substs(Substs::empty()), None)
        };

        let inlined_did = def_id.and_then(|def_id| inline::get_local_instance(ccx, def_id));
        let inlined_id = inlined_did.and_then(|id| ccx.tcx().map.as_local_node_id(id));
        let local_id = def_id.and_then(|id| ccx.tcx().map.as_local_node_id(id));

        debug!("FunctionContext::new({})",
               definition.map_or(String::new(), |d| d.0.to_string()));

        let cfg = inlined_id.map(|id| build_cfg(ccx.tcx(), id));
        let nested_returns = if let Some((blk_id, Some(ref cfg))) = cfg {
            has_nested_returns(ccx.tcx(), cfg, blk_id)
        } else {
            false
        };

        let check_attrs = |attrs: &[ast::Attribute]| {
            let default_to_mir = ccx.sess().opts.debugging_opts.orbit;
            let invert = if default_to_mir { "rustc_no_mir" } else { "rustc_mir" };
            (default_to_mir ^ attrs.iter().any(|item| item.check_name(invert)),
             attrs.iter().any(|item| item.check_name("no_debug")))
        };

        let (use_mir, no_debug) = if let Some(id) = local_id {
            check_attrs(ccx.tcx().map.attrs(id))
        } else if let Some(def_id) = def_id {
            check_attrs(&ccx.sess().cstore.item_attrs(def_id))
        } else {
            check_attrs(&[])
        };

        let mir = if use_mir {
            def_id.and_then(|id| ccx.get_mir(id))
        } else {
            None
        };

        let debug_context = if let (false, Some(definition)) = (no_debug, definition) {
            let (instance, sig, abi) = definition;
            debuginfo::create_function_debug_context(ccx, instance, sig, abi, llfndecl)
        } else {
            debuginfo::empty_function_debug_context(ccx)
        };

        FunctionContext {
            needs_ret_allocas: nested_returns && mir.is_none(),
            mir: mir,
            llfn: llfndecl,
            llretslotptr: Cell::new(None),
            param_env: ccx.tcx().empty_parameter_environment(),
            alloca_insert_pt: Cell::new(None),
            llreturn: Cell::new(None),
            landingpad_alloca: Cell::new(None),
            lllocals: RefCell::new(NodeMap()),
            llupvars: RefCell::new(NodeMap()),
            lldropflag_hints: RefCell::new(DropFlagHintsMap::new()),
            fn_ty: fn_ty,
            param_substs: param_substs,
            span: inlined_id.and_then(|id| ccx.tcx().map.opt_span(id)),
            block_arena: block_arena,
            lpad_arena: TypedArena::new(),
            ccx: ccx,
            debug_context: debug_context,
            scopes: RefCell::new(Vec::new()),
            cfg: cfg.and_then(|(_, cfg)| cfg)
        }
    }

    /// Performs setup on a newly created function, creating the entry
    /// scope block and allocating space for the return pointer.
    pub fn init(&'blk self, skip_retptr: bool, fn_did: Option<DefId>)
                -> Block<'blk, 'tcx> {
        let entry_bcx = self.new_temp_block("entry-block");

        // Use a dummy instruction as the insertion point for all allocas.
        // This is later removed in FunctionContext::cleanup.
        self.alloca_insert_pt.set(Some(unsafe {
            Load(entry_bcx, C_null(Type::i8p(self.ccx)));
            llvm::LLVMGetFirstInstruction(entry_bcx.llbb)
        }));

        if !self.fn_ty.ret.is_ignore() && !skip_retptr {
            // We normally allocate the llretslotptr, unless we
            // have been instructed to skip it for immediate return
            // values, or there is nothing to return at all.

            // We create an alloca to hold a pointer of type `ret.original_ty`
            // which will hold the pointer to the right alloca which has the
            // final ret value
            let llty = self.fn_ty.ret.memory_ty(self.ccx);
            let slot = if self.needs_ret_allocas {
                // Let's create the stack slot
                let slot = AllocaFcx(self, llty.ptr_to(), "llretslotptr");

                // and if we're using an out pointer, then store that in our newly made slot
                if self.fn_ty.ret.is_indirect() {
                    let outptr = get_param(self.llfn, 0);

                    let b = self.ccx.builder();
                    b.position_before(self.alloca_insert_pt.get().unwrap());
                    b.store(outptr, slot);
                }

                slot
            } else {
                // But if there are no nested returns, we skip the indirection
                // and have a single retslot
                if self.fn_ty.ret.is_indirect() {
                    get_param(self.llfn, 0)
                } else {
                    AllocaFcx(self, llty, "sret_slot")
                }
            };

            self.llretslotptr.set(Some(slot));
        }

        // Create the drop-flag hints for every unfragmented path in the function.
        let tcx = self.ccx.tcx();
        let tables = tcx.tables.borrow();
        let mut hints = self.lldropflag_hints.borrow_mut();
        let fragment_infos = tcx.fragment_infos.borrow();

        // Intern table for drop-flag hint datums.
        let mut seen = HashMap::new();

        let fragment_infos = fn_did.and_then(|did| fragment_infos.get(&did));
        if let Some(fragment_infos) = fragment_infos {
            for &info in fragment_infos {

                let make_datum = |id| {
                    let init_val = C_u8(self.ccx, adt::DTOR_NEEDED_HINT);
                    let llname = &format!("dropflag_hint_{}", id);
                    debug!("adding hint {}", llname);
                    let ty = tcx.types.u8;
                    let ptr = alloc_ty(entry_bcx, ty, llname);
                    Store(entry_bcx, init_val, ptr);
                    let flag = datum::Lvalue::new_dropflag_hint("FunctionContext::init");
                    datum::Datum::new(ptr, ty, flag)
                };

                let (var, datum) = match info {
                    ty::FragmentInfo::Moved { var, .. } |
                    ty::FragmentInfo::Assigned { var, .. } => {
                        let opt_datum = seen.get(&var).cloned().unwrap_or_else(|| {
                            let ty = tables.node_types[&var];
                            if self.type_needs_drop(ty) {
                                let datum = make_datum(var);
                                seen.insert(var, Some(datum.clone()));
                                Some(datum)
                            } else {
                                // No drop call needed, so we don't need a dropflag hint
                                None
                            }
                        });
                        if let Some(datum) = opt_datum {
                            (var, datum)
                        } else {
                            continue
                        }
                    }
                };
                match info {
                    ty::FragmentInfo::Moved { move_expr: expr_id, .. } => {
                        debug!("FragmentInfo::Moved insert drop hint for {}", expr_id);
                        hints.insert(expr_id, DropHint::new(var, datum));
                    }
                    ty::FragmentInfo::Assigned { assignee_id: expr_id, .. } => {
                        debug!("FragmentInfo::Assigned insert drop hint for {}", expr_id);
                        hints.insert(expr_id, DropHint::new(var, datum));
                    }
                }
            }
        }

        entry_bcx
    }

    /// Creates lvalue datums for each of the incoming function arguments,
    /// matches all argument patterns against them to produce bindings,
    /// and returns the entry block (see FunctionContext::init).
    fn bind_args(&'blk self,
                 args: &[hir::Arg],
                 abi: Abi,
                 id: ast::NodeId,
                 closure_env: closure::ClosureEnv,
                 arg_scope: cleanup::CustomScopeIndex)
                 -> Block<'blk, 'tcx> {
        let _icx = push_ctxt("FunctionContext::bind_args");
        let fn_did = self.ccx.tcx().map.local_def_id(id);
        let mut bcx = self.init(false, Some(fn_did));
        let arg_scope_id = cleanup::CustomScope(arg_scope);

        let mut idx = 0;
        let mut llarg_idx = self.fn_ty.ret.is_indirect() as usize;

        let has_tupled_arg = match closure_env {
            closure::ClosureEnv::NotClosure => abi == Abi::RustCall,
            closure::ClosureEnv::Closure(..) => {
                closure_env.load(bcx, arg_scope_id);
                let env_arg = &self.fn_ty.args[idx];
                idx += 1;
                if env_arg.pad.is_some() {
                    llarg_idx += 1;
                }
                if !env_arg.is_ignore() {
                    llarg_idx += 1;
                }
                false
            }
        };
        let tupled_arg_id = if has_tupled_arg {
            args[args.len() - 1].id
        } else {
            ast::DUMMY_NODE_ID
        };

        // Return an array wrapping the ValueRefs that we get from `get_param` for
        // each argument into datums.
        //
        // For certain mode/type combinations, the raw llarg values are passed
        // by value.  However, within the fn body itself, we want to always
        // have all locals and arguments be by-ref so that we can cancel the
        // cleanup and for better interaction with LLVM's debug info.  So, if
        // the argument would be passed by value, we store it into an alloca.
        // This alloca should be optimized away by LLVM's mem-to-reg pass in
        // the event it's not truly needed.
        let uninit_reason = InitAlloca::Uninit("fn_arg populate dominates dtor");
        for hir_arg in args {
            let arg_ty = node_id_type(bcx, hir_arg.id);
            let arg_datum = if hir_arg.id != tupled_arg_id {
                let arg = &self.fn_ty.args[idx];
                idx += 1;
                if arg.is_indirect() && bcx.sess().opts.debuginfo != FullDebugInfo {
                    // Don't copy an indirect argument to an alloca, the caller
                    // already put it in a temporary alloca and gave it up, unless
                    // we emit extra-debug-info, which requires local allocas :(.
                    let llarg = get_param(self.llfn, llarg_idx as c_uint);
                    llarg_idx += 1;
                    self.schedule_lifetime_end(arg_scope_id, llarg);
                    self.schedule_drop_mem(arg_scope_id, llarg, arg_ty, None);

                    datum::Datum::new(llarg,
                                    arg_ty,
                                    datum::Lvalue::new("FunctionContext::bind_args"))
                } else {
                    unpack_datum!(bcx, datum::lvalue_scratch_datum(bcx, arg_ty, "",
                                                                   uninit_reason,
                                                                   arg_scope_id, |bcx, dst| {
                        debug!("FunctionContext::bind_args: {:?}: {:?}", hir_arg, arg_ty);
                        let b = &bcx.build();
                        if common::type_is_fat_ptr(bcx.tcx(), arg_ty) {
                            let meta = &self.fn_ty.args[idx];
                            idx += 1;
                            arg.store_fn_arg(b, &mut llarg_idx, expr::get_dataptr(bcx, dst));
                            meta.store_fn_arg(b, &mut llarg_idx, expr::get_meta(bcx, dst));
                        } else {
                            arg.store_fn_arg(b, &mut llarg_idx, dst);
                        }
                        bcx
                    }))
                }
            } else {
                // FIXME(pcwalton): Reduce the amount of code bloat this is responsible for.
                let tupled_arg_tys = match arg_ty.sty {
                    ty::TyTuple(ref tys) => tys,
                    _ => bug!("last argument of `rust-call` fn isn't a tuple?!")
                };

                unpack_datum!(bcx, datum::lvalue_scratch_datum(bcx,
                                                            arg_ty,
                                                            "tupled_args",
                                                            uninit_reason,
                                                            arg_scope_id,
                                                            |bcx, llval| {
                    debug!("FunctionContext::bind_args: tupled {:?}: {:?}", hir_arg, arg_ty);
                    for (j, &tupled_arg_ty) in tupled_arg_tys.iter().enumerate() {
                        let dst = StructGEP(bcx, llval, j);
                        let arg = &self.fn_ty.args[idx];
                        idx += 1;
                        let b = &bcx.build();
                        if common::type_is_fat_ptr(bcx.tcx(), tupled_arg_ty) {
                            let meta = &self.fn_ty.args[idx];
                            idx += 1;
                            arg.store_fn_arg(b, &mut llarg_idx, expr::get_dataptr(bcx, dst));
                            meta.store_fn_arg(b, &mut llarg_idx, expr::get_meta(bcx, dst));
                        } else {
                            arg.store_fn_arg(b, &mut llarg_idx, dst);
                        }
                    }
                    bcx
                }))
            };

            let pat = &hir_arg.pat;
            bcx = if let Some(name) = simple_name(pat) {
                // Generate nicer LLVM for the common case of fn a pattern
                // like `x: T`
                set_value_name(arg_datum.val, &bcx.name(name));
                self.lllocals.borrow_mut().insert(pat.id, arg_datum);
                bcx
            } else {
                // General path. Copy out the values that are used in the
                // pattern.
                _match::bind_irrefutable_pat(bcx, pat, arg_datum.match_input(), arg_scope_id)
            };
            debuginfo::create_argument_metadata(bcx, hir_arg);
        }

        bcx
    }

    /// Ties up the llstaticallocas -> llloadenv -> lltop edges,
    /// and builds the return block.
    pub fn finish(&'blk self, last_bcx: Block<'blk, 'tcx>,
                  ret_debug_loc: DebugLoc) {
        let _icx = push_ctxt("FunctionContext::finish");

        let ret_cx = match self.llreturn.get() {
            Some(llreturn) => {
                if !last_bcx.terminated.get() {
                    Br(last_bcx, llreturn, DebugLoc::None);
                }
                raw_block(self, llreturn)
            }
            None => last_bcx,
        };

        self.build_return_block(ret_cx, ret_debug_loc);

        DebugLoc::None.apply(self);
        self.cleanup();
    }

    // Builds the return block for a function.
    pub fn build_return_block(&self, ret_cx: Block<'blk, 'tcx>,
                              ret_debug_location: DebugLoc) {
        if self.llretslotptr.get().is_none() ||
           ret_cx.unreachable.get() ||
           (!self.needs_ret_allocas && self.fn_ty.ret.is_indirect()) {
            return RetVoid(ret_cx, ret_debug_location);
        }

        let retslot = if self.needs_ret_allocas {
            Load(ret_cx, self.llretslotptr.get().unwrap())
        } else {
            self.llretslotptr.get().unwrap()
        };
        let retptr = Value(retslot);
        let llty = self.fn_ty.ret.original_ty;
        match (retptr.get_dominating_store(ret_cx), self.fn_ty.ret.cast) {
            // If there's only a single store to the ret slot, we can directly return
            // the value that was stored and omit the store and the alloca.
            // However, we only want to do this when there is no cast needed.
            (Some(s), None) => {
                let mut retval = s.get_operand(0).unwrap().get();
                s.erase_from_parent();

                if retptr.has_no_uses() {
                    retptr.erase_from_parent();
                }

                if self.fn_ty.ret.is_indirect() {
                    Store(ret_cx, retval, get_param(self.llfn, 0));
                    RetVoid(ret_cx, ret_debug_location)
                } else {
                    if llty == Type::i1(self.ccx) {
                        retval = Trunc(ret_cx, retval, llty);
                    }
                    Ret(ret_cx, retval, ret_debug_location)
                }
            }
            (_, cast_ty) if self.fn_ty.ret.is_indirect() => {
                // Otherwise, copy the return value to the ret slot.
                assert_eq!(cast_ty, None);
                let llsz = llsize_of(self.ccx, self.fn_ty.ret.ty);
                let llalign = llalign_of_min(self.ccx, self.fn_ty.ret.ty);
                call_memcpy(&B(ret_cx), get_param(self.llfn, 0),
                            retslot, llsz, llalign as u32);
                RetVoid(ret_cx, ret_debug_location)
            }
            (_, Some(cast_ty)) => {
                let load = Load(ret_cx, PointerCast(ret_cx, retslot, cast_ty.ptr_to()));
                let llalign = llalign_of_min(self.ccx, self.fn_ty.ret.ty);
                unsafe {
                    llvm::LLVMSetAlignment(load, llalign);
                }
                Ret(ret_cx, load, ret_debug_location)
            }
            (_, None) => {
                let retval = if llty == Type::i1(self.ccx) {
                    let val = LoadRangeAssert(ret_cx, retslot, 0, 2, llvm::False);
                    Trunc(ret_cx, val, llty)
                } else {
                    Load(ret_cx, retslot)
                };
                Ret(ret_cx, retval, ret_debug_location)
            }
        }
    }
}

/// Builds an LLVM function out of a source function.
///
/// If the function closes over its environment a closure will be returned.
pub fn trans_closure<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
                               decl: &hir::FnDecl,
                               body: &hir::Block,
                               llfndecl: ValueRef,
                               instance: Instance<'tcx>,
                               inlined_id: ast::NodeId,
                               sig: &ty::FnSig<'tcx>,
                               abi: Abi,
                               closure_env: closure::ClosureEnv) {
    ccx.stats().n_closures.set(ccx.stats().n_closures.get() + 1);

    if collector::collecting_debug_information(ccx) {
        ccx.record_translation_item_as_generated(TransItem::Fn(instance));
    }

    let _icx = push_ctxt("trans_closure");
    attributes::emit_uwtable(llfndecl, true);

    debug!("trans_closure(..., {})", instance);

    let fn_ty = FnType::new(ccx, abi, sig, &[]);

    let (arena, fcx): (TypedArena<_>, FunctionContext);
    arena = TypedArena::new();
    fcx = FunctionContext::new(ccx, llfndecl, fn_ty, Some((instance, sig, abi)), &arena);

    if fcx.mir.is_some() {
        return mir::trans_mir(&fcx);
    }

    debuginfo::fill_scope_map_for_function(&fcx, decl, body, inlined_id);

    // cleanup scope for the incoming arguments
    let fn_cleanup_debug_loc = debuginfo::get_cleanup_debug_loc_for_ast_node(
        ccx, inlined_id, body.span, true);
    let arg_scope = fcx.push_custom_cleanup_scope_with_debug_loc(fn_cleanup_debug_loc);

    // Set up arguments to the function.
    debug!("trans_closure: function: {:?}", Value(fcx.llfn));
    let bcx = fcx.bind_args(&decl.inputs, abi, inlined_id, closure_env, arg_scope);

    // Up until here, IR instructions for this function have explicitly not been annotated with
    // source code location, so we don't step into call setup code. From here on, source location
    // emitting should be enabled.
    debuginfo::start_emitting_source_locations(&fcx);

    let dest = if fcx.fn_ty.ret.is_ignore() {
        expr::Ignore
    } else {
        expr::SaveIn(fcx.get_ret_slot(bcx, "iret_slot"))
    };

    // This call to trans_block is the place where we bridge between
    // translation calls that don't have a return value (trans_crate,
    // trans_mod, trans_item, et cetera) and those that do
    // (trans_block, trans_expr, et cetera).
    let mut bcx = controlflow::trans_block(bcx, body, dest);

    match dest {
        expr::SaveIn(slot) if fcx.needs_ret_allocas => {
            Store(bcx, slot, fcx.llretslotptr.get().unwrap());
        }
        _ => {}
    }

    match fcx.llreturn.get() {
        Some(_) => {
            Br(bcx, fcx.return_exit_block(), DebugLoc::None);
            fcx.pop_custom_cleanup_scope(arg_scope);
        }
        None => {
            // Microoptimization writ large: avoid creating a separate
            // llreturn basic block
            bcx = fcx.pop_and_trans_custom_cleanup_scope(bcx, arg_scope);
        }
    };

    // Put return block after all other blocks.
    // This somewhat improves single-stepping experience in debugger.
    unsafe {
        let llreturn = fcx.llreturn.get();
        if let Some(llreturn) = llreturn {
            llvm::LLVMMoveBasicBlockAfter(llreturn, bcx.llbb);
        }
    }

    // Insert the mandatory first few basic blocks before lltop.
    fcx.finish(bcx, fn_cleanup_debug_loc.debug_loc());
}

/// Creates an LLVM function corresponding to a source language function.
pub fn trans_fn<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
                          decl: &hir::FnDecl,
                          body: &hir::Block,
                          llfndecl: ValueRef,
                          param_substs: &'tcx Substs<'tcx>,
                          id: ast::NodeId) {
    let _s = StatRecorder::new(ccx, ccx.tcx().node_path_str(id));
    debug!("trans_fn(param_substs={:?})", param_substs);
    let _icx = push_ctxt("trans_fn");
    let def_id = if let Some(&def_id) = ccx.external_srcs().borrow().get(&id) {
        def_id
    } else {
        ccx.tcx().map.local_def_id(id)
    };
    let fn_ty = ccx.tcx().lookup_item_type(def_id).ty;
    let fn_ty = monomorphize::apply_param_substs(ccx.tcx(), param_substs, &fn_ty);
    let sig = ccx.tcx().erase_late_bound_regions(fn_ty.fn_sig());
    let sig = infer::normalize_associated_type(ccx.tcx(), &sig);
    let abi = fn_ty.fn_abi();
    trans_closure(ccx,
                  decl,
                  body,
                  llfndecl,
                  Instance::new(def_id, param_substs),
                  id,
                  &sig,
                  abi,
                  closure::ClosureEnv::NotClosure);
}

pub fn trans_named_tuple_constructor<'blk, 'tcx>(mut bcx: Block<'blk, 'tcx>,
                                                 ctor_ty: Ty<'tcx>,
                                                 disr: Disr,
                                                 args: CallArgs,
                                                 dest: expr::Dest,
                                                 debug_loc: DebugLoc)
                                                 -> Result<'blk, 'tcx> {

    let ccx = bcx.fcx.ccx;

    let sig = ccx.tcx().erase_late_bound_regions(&ctor_ty.fn_sig());
    let sig = infer::normalize_associated_type(ccx.tcx(), &sig);
    let result_ty = sig.output.unwrap();

    // Get location to store the result. If the user does not care about
    // the result, just make a stack slot
    let llresult = match dest {
        expr::SaveIn(d) => d,
        expr::Ignore => {
            if !type_is_zero_size(ccx, result_ty) {
                let llresult = alloc_ty(bcx, result_ty, "constructor_result");
                call_lifetime_start(bcx, llresult);
                llresult
            } else {
                C_undef(type_of::type_of(ccx, result_ty).ptr_to())
            }
        }
    };

    if !type_is_zero_size(ccx, result_ty) {
        match args {
            ArgExprs(exprs) => {
                let fields = exprs.iter().map(|x| &**x).enumerate().collect::<Vec<_>>();
                bcx = expr::trans_adt(bcx,
                                      result_ty,
                                      disr,
                                      &fields[..],
                                      None,
                                      expr::SaveIn(llresult),
                                      debug_loc);
            }
            _ => bug!("expected expr as arguments for variant/struct tuple constructor"),
        }
    } else {
        // Just eval all the expressions (if any). Since expressions in Rust can have arbitrary
        // contents, there could be side-effects we need from them.
        match args {
            ArgExprs(exprs) => {
                for expr in exprs {
                    bcx = expr::trans_into(bcx, expr, expr::Ignore);
                }
            }
            _ => (),
        }
    }

    // If the caller doesn't care about the result
    // drop the temporary we made
    let bcx = match dest {
        expr::SaveIn(_) => bcx,
        expr::Ignore => {
            let bcx = glue::drop_ty(bcx, llresult, result_ty, debug_loc);
            if !type_is_zero_size(ccx, result_ty) {
                call_lifetime_end(bcx, llresult);
            }
            bcx
        }
    };

    Result::new(bcx, llresult)
}

pub fn trans_ctor_shim<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
                                 ctor_id: ast::NodeId,
                                 disr: Disr,
                                 param_substs: &'tcx Substs<'tcx>,
                                 llfndecl: ValueRef) {
    let ctor_ty = ccx.tcx().node_id_to_type(ctor_id);
    let ctor_ty = monomorphize::apply_param_substs(ccx.tcx(), param_substs, &ctor_ty);

    let sig = ccx.tcx().erase_late_bound_regions(&ctor_ty.fn_sig());
    let sig = infer::normalize_associated_type(ccx.tcx(), &sig);
    let fn_ty = FnType::new(ccx, Abi::Rust, &sig, &[]);

    let (arena, fcx): (TypedArena<_>, FunctionContext);
    arena = TypedArena::new();
    fcx = FunctionContext::new(ccx, llfndecl, fn_ty, None, &arena);
    let bcx = fcx.init(false, None);

    assert!(!fcx.needs_ret_allocas);

    if !fcx.fn_ty.ret.is_ignore() {
        let dest = fcx.get_ret_slot(bcx, "eret_slot");
        let dest_val = adt::MaybeSizedValue::sized(dest); // Can return unsized value
        let repr = adt::represent_type(ccx, sig.output.unwrap());
        let mut llarg_idx = fcx.fn_ty.ret.is_indirect() as usize;
        let mut arg_idx = 0;
        for (i, arg_ty) in sig.inputs.into_iter().enumerate() {
            let lldestptr = adt::trans_field_ptr(bcx, &repr, dest_val, Disr::from(disr), i);
            let arg = &fcx.fn_ty.args[arg_idx];
            arg_idx += 1;
            let b = &bcx.build();
            if common::type_is_fat_ptr(bcx.tcx(), arg_ty) {
                let meta = &fcx.fn_ty.args[arg_idx];
                arg_idx += 1;
                arg.store_fn_arg(b, &mut llarg_idx, expr::get_dataptr(bcx, lldestptr));
                meta.store_fn_arg(b, &mut llarg_idx, expr::get_meta(bcx, lldestptr));
            } else {
                arg.store_fn_arg(b, &mut llarg_idx, lldestptr);
            }
        }
        adt::trans_set_discr(bcx, &repr, dest, disr);
    }

    fcx.finish(bcx, DebugLoc::None);
}

fn enum_variant_size_lint(ccx: &CrateContext, enum_def: &hir::EnumDef, sp: Span, id: ast::NodeId) {
    let mut sizes = Vec::new(); // does no allocation if no pushes, thankfully

    let print_info = ccx.sess().print_enum_sizes();

    let levels = ccx.tcx().node_lint_levels.borrow();
    let lint_id = lint::LintId::of(lint::builtin::VARIANT_SIZE_DIFFERENCES);
    let lvlsrc = levels.get(&(id, lint_id));
    let is_allow = lvlsrc.map_or(true, |&(lvl, _)| lvl == lint::Allow);

    if is_allow && !print_info {
        // we're not interested in anything here
        return;
    }

    let ty = ccx.tcx().node_id_to_type(id);
    let avar = adt::represent_type(ccx, ty);
    match *avar {
        adt::General(_, ref variants, _) => {
            for var in variants {
                let mut size = 0;
                for field in var.fields.iter().skip(1) {
                    // skip the discriminant
                    size += llsize_of_real(ccx, sizing_type_of(ccx, *field));
                }
                sizes.push(size);
            }
        },
        _ => { /* its size is either constant or unimportant */ }
    }

    let (largest, slargest, largest_index) = sizes.iter().enumerate().fold((0, 0, 0),
        |(l, s, li), (idx, &size)|
            if size > l {
                (size, l, idx)
            } else if size > s {
                (l, size, li)
            } else {
                (l, s, li)
            }
    );

    // FIXME(#30505) Should use logging for this.
    if print_info {
        let llty = type_of::sizing_type_of(ccx, ty);

        let sess = &ccx.tcx().sess;
        sess.span_note_without_error(sp,
                                     &format!("total size: {} bytes", llsize_of_real(ccx, llty)));
        match *avar {
            adt::General(..) => {
                for (i, var) in enum_def.variants.iter().enumerate() {
                    ccx.tcx()
                       .sess
                       .span_note_without_error(var.span,
                                                &format!("variant data: {} bytes", sizes[i]));
                }
            }
            _ => {}
        }
    }

    // we only warn if the largest variant is at least thrice as large as
    // the second-largest.
    if !is_allow && largest > slargest * 3 && slargest > 0 {
        // Use lint::raw_emit_lint rather than sess.add_lint because the lint-printing
        // pass for the latter already ran.
        lint::raw_struct_lint(&ccx.tcx().sess,
                              &ccx.tcx().sess.lint_store.borrow(),
                              lint::builtin::VARIANT_SIZE_DIFFERENCES,
                              *lvlsrc.unwrap(),
                              Some(sp),
                              &format!("enum variant is more than three times larger ({} bytes) \
                                        than the next largest (ignoring padding)",
                                       largest))
            .span_note(enum_def.variants[largest_index].span,
                       "this variant is the largest")
            .emit();
    }
}

pub fn llvm_linkage_by_name(name: &str) -> Option<Linkage> {
    // Use the names from src/llvm/docs/LangRef.rst here. Most types are only
    // applicable to variable declarations and may not really make sense for
    // Rust code in the first place but whitelist them anyway and trust that
    // the user knows what s/he's doing. Who knows, unanticipated use cases
    // may pop up in the future.
    //
    // ghost, dllimport, dllexport and linkonce_odr_autohide are not supported
    // and don't have to be, LLVM treats them as no-ops.
    match name {
        "appending" => Some(llvm::AppendingLinkage),
        "available_externally" => Some(llvm::AvailableExternallyLinkage),
        "common" => Some(llvm::CommonLinkage),
        "extern_weak" => Some(llvm::ExternalWeakLinkage),
        "external" => Some(llvm::ExternalLinkage),
        "internal" => Some(llvm::InternalLinkage),
        "linkonce" => Some(llvm::LinkOnceAnyLinkage),
        "linkonce_odr" => Some(llvm::LinkOnceODRLinkage),
        "private" => Some(llvm::PrivateLinkage),
        "weak" => Some(llvm::WeakAnyLinkage),
        "weak_odr" => Some(llvm::WeakODRLinkage),
        _ => None,
    }
}


/// Enum describing the origin of an LLVM `Value`, for linkage purposes.
#[derive(Copy, Clone)]
pub enum ValueOrigin {
    /// The LLVM `Value` is in this context because the corresponding item was
    /// assigned to the current compilation unit.
    OriginalTranslation,
    /// The `Value`'s corresponding item was assigned to some other compilation
    /// unit, but the `Value` was translated in this context anyway because the
    /// item is marked `#[inline]`.
    InlinedCopy,
}

/// Set the appropriate linkage for an LLVM `ValueRef` (function or global).
/// If the `llval` is the direct translation of a specific Rust item, `id`
/// should be set to the `NodeId` of that item.  (This mapping should be
/// 1-to-1, so monomorphizations and drop/visit glue should have `id` set to
/// `None`.)  `llval_origin` indicates whether `llval` is the translation of an
/// item assigned to `ccx`'s compilation unit or an inlined copy of an item
/// assigned to a different compilation unit.
pub fn update_linkage(ccx: &CrateContext,
                      llval: ValueRef,
                      id: Option<ast::NodeId>,
                      llval_origin: ValueOrigin) {
    match llval_origin {
        InlinedCopy => {
            // `llval` is a translation of an item defined in a separate
            // compilation unit.  This only makes sense if there are at least
            // two compilation units.
            assert!(ccx.sess().opts.cg.codegen_units > 1);
            // `llval` is a copy of something defined elsewhere, so use
            // `AvailableExternallyLinkage` to avoid duplicating code in the
            // output.
            llvm::SetLinkage(llval, llvm::AvailableExternallyLinkage);
            return;
        },
        OriginalTranslation => {},
    }

    if let Some(id) = id {
        let item = ccx.tcx().map.get(id);
        if let hir_map::NodeItem(i) = item {
            if let Some(name) = attr::first_attr_value_str_by_name(&i.attrs, "linkage") {
                if let Some(linkage) = llvm_linkage_by_name(&name) {
                    llvm::SetLinkage(llval, linkage);
                } else {
                    ccx.sess().span_fatal(i.span, "invalid linkage specified");
                }
                return;
            }
        }
    }

    let (is_reachable, is_generic) = if let Some(id) = id {
        (ccx.reachable().contains(&id), false)
    } else {
        (false, true)
    };

    // We need external linkage for items reachable from other translation units, this include
    // other codegen units in case of parallel compilations.
    if is_reachable || ccx.sess().opts.cg.codegen_units > 1 {
        if is_generic {
            // This only happens with multiple codegen units, in which case we need to use weak_odr
            // linkage because other crates might expose the same symbol. We cannot use
            // linkonce_odr here because the symbol might then get dropped before the other codegen
            // units get to link it.
            llvm::SetUniqueComdat(ccx.llmod(), llval);
            llvm::SetLinkage(llval, llvm::WeakODRLinkage);
        } else {
            llvm::SetLinkage(llval, llvm::ExternalLinkage);
        }
    } else {
        llvm::SetLinkage(llval, llvm::InternalLinkage);
    }
}

fn set_global_section(ccx: &CrateContext, llval: ValueRef, i: &hir::Item) {
    match attr::first_attr_value_str_by_name(&i.attrs, "link_section") {
        Some(sect) => {
            if contains_null(&sect) {
                ccx.sess().fatal(&format!("Illegal null byte in link_section value: `{}`", &sect));
            }
            unsafe {
                let buf = CString::new(sect.as_bytes()).unwrap();
                llvm::LLVMSetSection(llval, buf.as_ptr());
            }
        },
        None => ()
    }
}

pub fn trans_item(ccx: &CrateContext, item: &hir::Item) {
    let _icx = push_ctxt("trans_item");

    let tcx = ccx.tcx();
    let from_external = ccx.external_srcs().borrow().contains_key(&item.id);

    match item.node {
        hir::ItemFn(ref decl, _, _, _, ref generics, ref body) => {
            if !generics.is_type_parameterized() {
                let trans_everywhere = attr::requests_inline(&item.attrs);
                // Ignore `trans_everywhere` for cross-crate inlined items
                // (`from_external`).  `trans_item` will be called once for each
                // compilation unit that references the item, so it will still get
                // translated everywhere it's needed.
                for (ref ccx, is_origin) in ccx.maybe_iter(!from_external && trans_everywhere) {
                    let def_id = tcx.map.local_def_id(item.id);
                    let empty_substs = ccx.empty_substs_for_def_id(def_id);
                    let llfn = Callee::def(ccx, def_id, empty_substs).reify(ccx).val;
                    trans_fn(ccx, &decl, &body, llfn, empty_substs, item.id);
                    set_global_section(ccx, llfn, item);
                    update_linkage(ccx,
                                   llfn,
                                   Some(item.id),
                                   if is_origin {
                                       OriginalTranslation
                                   } else {
                                       InlinedCopy
                                   });

                    if is_entry_fn(ccx.sess(), item.id) {
                        create_entry_wrapper(ccx, item.span, llfn);
                        // check for the #[rustc_error] annotation, which forces an
                        // error in trans. This is used to write compile-fail tests
                        // that actually test that compilation succeeds without
                        // reporting an error.
                        if tcx.has_attr(def_id, "rustc_error") {
                            tcx.sess.span_fatal(item.span, "compilation successful");
                        }
                    }
                }
            }
        }
        hir::ItemImpl(_, _, ref generics, _, _, ref impl_items) => {
            // Both here and below with generic methods, be sure to recurse and look for
            // items that we need to translate.
            if !generics.ty_params.is_empty() {
                return;
            }

            for impl_item in impl_items {
                if let hir::ImplItemKind::Method(ref sig, ref body) = impl_item.node {
                    if sig.generics.ty_params.is_empty() {
                        let trans_everywhere = attr::requests_inline(&impl_item.attrs);
                        for (ref ccx, is_origin) in ccx.maybe_iter(trans_everywhere) {
                            let def_id = tcx.map.local_def_id(impl_item.id);
                            let empty_substs = ccx.empty_substs_for_def_id(def_id);
                            let llfn = Callee::def(ccx, def_id, empty_substs).reify(ccx).val;
                            trans_fn(ccx, &sig.decl, body, llfn, empty_substs, impl_item.id);
                            update_linkage(ccx, llfn, Some(impl_item.id),
                                if is_origin {
                                    OriginalTranslation
                                } else {
                                    InlinedCopy
                                });
                        }
                    }
                }
            }
        }
        hir::ItemEnum(ref enum_definition, ref gens) => {
            if gens.ty_params.is_empty() {
                // sizes only make sense for non-generic types
                enum_variant_size_lint(ccx, enum_definition, item.span, item.id);
            }
        }
        hir::ItemStatic(_, m, ref expr) => {
            let g = match consts::trans_static(ccx, m, expr, item.id, &item.attrs) {
                Ok(g) => g,
                Err(err) => ccx.tcx().sess.span_fatal(expr.span, &err.description()),
            };
            set_global_section(ccx, g, item);
            update_linkage(ccx, g, Some(item.id), OriginalTranslation);
        }
        hir::ItemForeignMod(ref m) => {
            if m.abi == Abi::RustIntrinsic || m.abi == Abi::PlatformIntrinsic {
                return;
            }
            for fi in &m.items {
                let lname = imported_name(fi.name, &fi.attrs).to_string();
                ccx.item_symbols().borrow_mut().insert(fi.id, lname);
            }
        }
        _ => {}
    }
}

pub fn is_entry_fn(sess: &Session, node_id: ast::NodeId) -> bool {
    match *sess.entry_fn.borrow() {
        Some((entry_id, _)) => node_id == entry_id,
        None => false,
    }
}

/// Create the `main` function which will initialise the rust runtime and call users’ main
/// function.
pub fn create_entry_wrapper(ccx: &CrateContext, sp: Span, main_llfn: ValueRef) {
    let et = ccx.sess().entry_type.get().unwrap();
    match et {
        config::EntryMain => {
            create_entry_fn(ccx, sp, main_llfn, true);
        }
        config::EntryStart => create_entry_fn(ccx, sp, main_llfn, false),
        config::EntryNone => {}    // Do nothing.
    }

    fn create_entry_fn(ccx: &CrateContext,
                       sp: Span,
                       rust_main: ValueRef,
                       use_start_lang_item: bool) {
        let llfty = Type::func(&[ccx.int_type(), Type::i8p(ccx).ptr_to()], &ccx.int_type());

        if declare::get_defined_value(ccx, "main").is_some() {
            // FIXME: We should be smart and show a better diagnostic here.
            ccx.sess().struct_span_err(sp, "entry symbol `main` defined multiple times")
                      .help("did you use #[no_mangle] on `fn main`? Use #[start] instead")
                      .emit();
            ccx.sess().abort_if_errors();
            bug!();
        }
        let llfn = declare::declare_cfn(ccx, "main", llfty);

        let llbb = unsafe {
            llvm::LLVMAppendBasicBlockInContext(ccx.llcx(), llfn, "top\0".as_ptr() as *const _)
        };
        let bld = ccx.raw_builder();
        unsafe {
            llvm::LLVMPositionBuilderAtEnd(bld, llbb);

            debuginfo::gdb::insert_reference_to_gdb_debug_scripts_section_global(ccx);

            let (start_fn, args) = if use_start_lang_item {
                let start_def_id = match ccx.tcx().lang_items.require(StartFnLangItem) {
                    Ok(id) => id,
                    Err(s) => ccx.sess().fatal(&s)
                };
                let empty_substs = ccx.tcx().mk_substs(Substs::empty());
                let start_fn = Callee::def(ccx, start_def_id, empty_substs).reify(ccx).val;
                let args = {
                    let opaque_rust_main =
                        llvm::LLVMBuildPointerCast(bld,
                                                   rust_main,
                                                   Type::i8p(ccx).to_ref(),
                                                   "rust_main\0".as_ptr() as *const _);

                    vec![opaque_rust_main, get_param(llfn, 0), get_param(llfn, 1)]
                };
                (start_fn, args)
            } else {
                debug!("using user-defined start fn");
                let args = vec![get_param(llfn, 0 as c_uint), get_param(llfn, 1 as c_uint)];

                (rust_main, args)
            };

            let result = llvm::LLVMRustBuildCall(bld,
                                                 start_fn,
                                                 args.as_ptr(),
                                                 args.len() as c_uint,
                                                 0 as *mut _,
                                                 noname());

            llvm::LLVMBuildRet(bld, result);
        }
    }
}

pub fn exported_name<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
                               instance: Instance<'tcx>,
                               attrs: &[ast::Attribute])
                               -> String {
    let id = ccx.tcx().map.as_local_node_id(instance.def).unwrap();

    match ccx.external_srcs().borrow().get(&id) {
        Some(&did) => {
            let sym = ccx.sess().cstore.item_symbol(did);
            debug!("found item {} in other crate...", sym);
            return sym;
        }
        None => {}
    }

    match attr::find_export_name_attr(ccx.sess().diagnostic(), attrs) {
        // Use provided name
        Some(name) => name.to_string(),
        _ => {
            if attr::contains_name(attrs, "no_mangle") {
                // Don't mangle
                ccx.tcx().map.name(id).as_str().to_string()
            } else {
                match weak_lang_items::link_name(attrs) {
                    Some(name) => name.to_string(),
                    None => {
                        // Usual name mangling
                        symbol_names::exported_name(ccx, &instance)
                    }
                }
            }
        }
    }
}

pub fn imported_name(name: ast::Name, attrs: &[ast::Attribute]) -> InternedString {
    match attr::first_attr_value_str_by_name(attrs, "link_name") {
        Some(ln) => ln.clone(),
        None => match weak_lang_items::link_name(attrs) {
            Some(name) => name,
            None => name.as_str(),
        }
    }
}

fn contains_null(s: &str) -> bool {
    s.bytes().any(|b| b == 0)
}

pub fn write_metadata<'a, 'tcx>(cx: &SharedCrateContext<'a, 'tcx>,
                                krate: &hir::Crate,
                                reachable: &NodeSet,
                                mir_map: &MirMap<'tcx>)
                                -> Vec<u8> {
    use flate;

    let any_library = cx.sess()
                        .crate_types
                        .borrow()
                        .iter()
                        .any(|ty| *ty != config::CrateTypeExecutable);
    if !any_library {
        return Vec::new();
    }

    let cstore = &cx.tcx().sess.cstore;
    let metadata = cstore.encode_metadata(cx.tcx(),
                                          cx.export_map(),
                                          cx.item_symbols(),
                                          cx.link_meta(),
                                          reachable,
                                          mir_map,
                                          krate);
    let mut compressed = cstore.metadata_encoding_version().to_vec();
    compressed.extend_from_slice(&flate::deflate_bytes(&metadata));

    let llmeta = C_bytes_in_context(cx.metadata_llcx(), &compressed[..]);
    let llconst = C_struct_in_context(cx.metadata_llcx(), &[llmeta], false);
    let name = format!("rust_metadata_{}_{}",
                       cx.link_meta().crate_name,
                       cx.link_meta().crate_hash);
    let buf = CString::new(name).unwrap();
    let llglobal = unsafe {
        llvm::LLVMAddGlobal(cx.metadata_llmod(), val_ty(llconst).to_ref(), buf.as_ptr())
    };
    unsafe {
        llvm::LLVMSetInitializer(llglobal, llconst);
        let name =
            cx.tcx().sess.cstore.metadata_section_name(&cx.sess().target.target);
        let name = CString::new(name).unwrap();
        llvm::LLVMSetSection(llglobal, name.as_ptr())
    }
    return metadata;
}

/// Find any symbols that are defined in one compilation unit, but not declared
/// in any other compilation unit.  Give these symbols internal linkage.
fn internalize_symbols(cx: &CrateContextList, reachable: &HashSet<&str>) {
    unsafe {
        let mut declared = HashSet::new();

        // Collect all external declarations in all compilation units.
        for ccx in cx.iter() {
            for val in iter_globals(ccx.llmod()).chain(iter_functions(ccx.llmod())) {
                let linkage = llvm::LLVMGetLinkage(val);
                // We only care about external declarations (not definitions)
                // and available_externally definitions.
                if !(linkage == llvm::ExternalLinkage as c_uint &&
                     llvm::LLVMIsDeclaration(val) != 0) &&
                   !(linkage == llvm::AvailableExternallyLinkage as c_uint) {
                    continue;
                }

                let name = CStr::from_ptr(llvm::LLVMGetValueName(val))
                               .to_bytes()
                               .to_vec();
                declared.insert(name);
            }
        }

        // Examine each external definition.  If the definition is not used in
        // any other compilation unit, and is not reachable from other crates,
        // then give it internal linkage.
        for ccx in cx.iter() {
            for val in iter_globals(ccx.llmod()).chain(iter_functions(ccx.llmod())) {
                let linkage = llvm::LLVMGetLinkage(val);
                // We only care about external definitions.
                if !((linkage == llvm::ExternalLinkage as c_uint ||
                      linkage == llvm::WeakODRLinkage as c_uint) &&
                     llvm::LLVMIsDeclaration(val) == 0) {
                    continue;
                }

                let name = CStr::from_ptr(llvm::LLVMGetValueName(val))
                               .to_bytes()
                               .to_vec();
                if !declared.contains(&name) &&
                   !reachable.contains(str::from_utf8(&name).unwrap()) {
                    llvm::SetLinkage(val, llvm::InternalLinkage);
                    llvm::SetDLLStorageClass(val, llvm::DefaultStorageClass);
                    llvm::UnsetComdat(val);
                }
            }
        }
    }
}

// Create a `__imp_<symbol> = &symbol` global for every public static `symbol`.
// This is required to satisfy `dllimport` references to static data in .rlibs
// when using MSVC linker.  We do this only for data, as linker can fix up
// code references on its own.
// See #26591, #27438
fn create_imps(cx: &CrateContextList) {
    // The x86 ABI seems to require that leading underscores are added to symbol
    // names, so we need an extra underscore on 32-bit. There's also a leading
    // '\x01' here which disables LLVM's symbol mangling (e.g. no extra
    // underscores added in front).
    let prefix = if cx.shared().sess().target.target.target_pointer_width == "32" {
        "\x01__imp__"
    } else {
        "\x01__imp_"
    };
    unsafe {
        for ccx in cx.iter() {
            let exported: Vec<_> = iter_globals(ccx.llmod())
                                       .filter(|&val| {
                                           llvm::LLVMGetLinkage(val) ==
                                           llvm::ExternalLinkage as c_uint &&
                                           llvm::LLVMIsDeclaration(val) == 0
                                       })
                                       .collect();

            let i8p_ty = Type::i8p(&ccx);
            for val in exported {
                let name = CStr::from_ptr(llvm::LLVMGetValueName(val));
                let mut imp_name = prefix.as_bytes().to_vec();
                imp_name.extend(name.to_bytes());
                let imp_name = CString::new(imp_name).unwrap();
                let imp = llvm::LLVMAddGlobal(ccx.llmod(),
                                              i8p_ty.to_ref(),
                                              imp_name.as_ptr() as *const _);
                let init = llvm::LLVMConstBitCast(val, i8p_ty.to_ref());
                llvm::LLVMSetInitializer(imp, init);
                llvm::SetLinkage(imp, llvm::ExternalLinkage);
            }
        }
    }
}

struct ValueIter {
    cur: ValueRef,
    step: unsafe extern "C" fn(ValueRef) -> ValueRef,
}

impl Iterator for ValueIter {
    type Item = ValueRef;

    fn next(&mut self) -> Option<ValueRef> {
        let old = self.cur;
        if !old.is_null() {
            self.cur = unsafe { (self.step)(old) };
            Some(old)
        } else {
            None
        }
    }
}

fn iter_globals(llmod: llvm::ModuleRef) -> ValueIter {
    unsafe {
        ValueIter {
            cur: llvm::LLVMGetFirstGlobal(llmod),
            step: llvm::LLVMGetNextGlobal,
        }
    }
}

fn iter_functions(llmod: llvm::ModuleRef) -> ValueIter {
    unsafe {
        ValueIter {
            cur: llvm::LLVMGetFirstFunction(llmod),
            step: llvm::LLVMGetNextFunction,
        }
    }
}

/// The context provided lists a set of reachable ids as calculated by
/// middle::reachable, but this contains far more ids and symbols than we're
/// actually exposing from the object file. This function will filter the set in
/// the context to the set of ids which correspond to symbols that are exposed
/// from the object file being generated.
///
/// This list is later used by linkers to determine the set of symbols needed to
/// be exposed from a dynamic library and it's also encoded into the metadata.
pub fn filter_reachable_ids(ccx: &SharedCrateContext) -> NodeSet {
    ccx.reachable().iter().map(|x| *x).filter(|id| {
        // First, only worry about nodes which have a symbol name
        ccx.item_symbols().borrow().contains_key(id)
    }).filter(|&id| {
        // Next, we want to ignore some FFI functions that are not exposed from
        // this crate. Reachable FFI functions can be lumped into two
        // categories:
        //
        // 1. Those that are included statically via a static library
        // 2. Those included otherwise (e.g. dynamically or via a framework)
        //
        // Although our LLVM module is not literally emitting code for the
        // statically included symbols, it's an export of our library which
        // needs to be passed on to the linker and encoded in the metadata.
        //
        // As a result, if this id is an FFI item (foreign item) then we only
        // let it through if it's included statically.
        match ccx.tcx().map.get(id) {
            hir_map::NodeForeignItem(..) => {
                ccx.sess().cstore.is_statically_included_foreign_item(id)
            }
            _ => true,
        }
    }).collect()
}

pub fn trans_crate<'tcx>(tcx: &TyCtxt<'tcx>,
                         mir_map: &MirMap<'tcx>,
                         analysis: ty::CrateAnalysis)
                         -> CrateTranslation {
    let _task = tcx.dep_graph.in_task(DepNode::TransCrate);

    // Be careful with this krate: obviously it gives access to the
    // entire contents of the krate. So if you push any subtasks of
    // `TransCrate`, you need to be careful to register "reads" of the
    // particular items that will be processed.
    let krate = tcx.map.krate();

    let ty::CrateAnalysis { export_map, reachable, name, .. } = analysis;

    let check_overflow = if let Some(v) = tcx.sess.opts.debugging_opts.force_overflow_checks {
        v
    } else {
        tcx.sess.opts.debug_assertions
    };

    let check_dropflag = if let Some(v) = tcx.sess.opts.debugging_opts.force_dropflag_checks {
        v
    } else {
        tcx.sess.opts.debug_assertions
    };

    let link_meta = link::build_link_meta(&tcx, name);

    let shared_ccx = SharedCrateContext::new(tcx,
                                             &mir_map,
                                             export_map,
                                             Sha256::new(),
                                             link_meta.clone(),
                                             reachable,
                                             check_overflow,
                                             check_dropflag);

    let codegen_units = tcx.sess.opts.cg.codegen_units;
    let crate_context_list = CrateContextList::new(&shared_ccx, codegen_units);

    {
        let ccx = crate_context_list.get_ccx(0);
        collect_translation_items(&ccx);

        // Translate all items. See `TransModVisitor` for
        // details on why we walk in this particular way.
        {
            let _icx = push_ctxt("text");
            intravisit::walk_mod(&mut TransItemsWithinModVisitor { ccx: &ccx }, &krate.module);
            krate.visit_all_items(&mut TransModVisitor { ccx: &ccx });
        }

        collector::print_collection_results(&ccx);

        symbol_names_test::report_symbol_names(&ccx);
    }

    for ccx in crate_context_list.iter() {
        if ccx.sess().opts.debuginfo != NoDebugInfo {
            debuginfo::finalize(&ccx);
        }
        for &(old_g, new_g) in ccx.statics_to_rauw().borrow().iter() {
            unsafe {
                let bitcast = llvm::LLVMConstPointerCast(new_g, llvm::LLVMTypeOf(old_g));
                llvm::LLVMReplaceAllUsesWith(old_g, bitcast);
                llvm::LLVMDeleteGlobal(old_g);
            }
        }
    }

    let reachable_symbol_ids = filter_reachable_ids(&shared_ccx);

    // Translate the metadata.
    let metadata = time(tcx.sess.time_passes(), "write metadata", || {
        write_metadata(&shared_ccx, krate, &reachable_symbol_ids, mir_map)
    });

    if shared_ccx.sess().trans_stats() {
        let stats = shared_ccx.stats();
        println!("--- trans stats ---");
        println!("n_glues_created: {}", stats.n_glues_created.get());
        println!("n_null_glues: {}", stats.n_null_glues.get());
        println!("n_real_glues: {}", stats.n_real_glues.get());

        println!("n_fns: {}", stats.n_fns.get());
        println!("n_monos: {}", stats.n_monos.get());
        println!("n_inlines: {}", stats.n_inlines.get());
        println!("n_closures: {}", stats.n_closures.get());
        println!("fn stats:");
        stats.fn_stats.borrow_mut().sort_by(|&(_, insns_a), &(_, insns_b)| {
            insns_b.cmp(&insns_a)
        });
        for tuple in stats.fn_stats.borrow().iter() {
            match *tuple {
                (ref name, insns) => {
                    println!("{} insns, {}", insns, *name);
                }
            }
        }
    }
    if shared_ccx.sess().count_llvm_insns() {
        for (k, v) in shared_ccx.stats().llvm_insns.borrow().iter() {
            println!("{:7} {}", *v, *k);
        }
    }

    let modules = crate_context_list.iter()
        .map(|ccx| ModuleTranslation { llcx: ccx.llcx(), llmod: ccx.llmod() })
        .collect();

    let sess = shared_ccx.sess();
    let mut reachable_symbols = reachable_symbol_ids.iter().map(|id| {
        shared_ccx.item_symbols().borrow()[id].to_string()
    }).collect::<Vec<_>>();
    if sess.entry_fn.borrow().is_some() {
        reachable_symbols.push("main".to_string());
    }

    // For the purposes of LTO, we add to the reachable set all of the upstream
    // reachable extern fns. These functions are all part of the public ABI of
    // the final product, so LTO needs to preserve them.
    if sess.lto() {
        for cnum in sess.cstore.crates() {
            let syms = sess.cstore.reachable_ids(cnum);
            reachable_symbols.extend(syms.into_iter().filter(|did| {
                sess.cstore.is_extern_item(shared_ccx.tcx(), *did)
            }).map(|did| {
                sess.cstore.item_symbol(did)
            }));
        }
    }

    if codegen_units > 1 {
        internalize_symbols(&crate_context_list,
                            &reachable_symbols.iter().map(|x| &x[..]).collect());
    }

    if sess.target.target.options.is_like_msvc &&
       sess.crate_types.borrow().iter().any(|ct| *ct == config::CrateTypeRlib) {
        create_imps(&crate_context_list);
    }

    let metadata_module = ModuleTranslation {
        llcx: shared_ccx.metadata_llcx(),
        llmod: shared_ccx.metadata_llmod(),
    };
    let no_builtins = attr::contains_name(&krate.attrs, "no_builtins");

    CrateTranslation {
        modules: modules,
        metadata_module: metadata_module,
        link: link_meta,
        metadata: metadata,
        reachable: reachable_symbols,
        no_builtins: no_builtins,
    }
}

/// We visit all the items in the krate and translate them.  We do
/// this in two walks. The first walk just finds module items. It then
/// walks the full contents of those module items and translates all
/// the items within. Note that this entire process is O(n). The
/// reason for this two phased walk is that each module is
/// (potentially) placed into a distinct codegen-unit. This walk also
/// ensures that the immediate contents of each module is processed
/// entirely before we proceed to find more modules, helping to ensure
/// an equitable distribution amongst codegen-units.
pub struct TransModVisitor<'a, 'tcx: 'a> {
    pub ccx: &'a CrateContext<'a, 'tcx>,
}

impl<'a, 'tcx, 'v> Visitor<'v> for TransModVisitor<'a, 'tcx> {
    fn visit_item(&mut self, i: &hir::Item) {
        match i.node {
            hir::ItemMod(_) => {
                let item_ccx = self.ccx.rotate();
                intravisit::walk_item(&mut TransItemsWithinModVisitor { ccx: &item_ccx }, i);
            }
            _ => { }
        }
    }
}

/// Translates all the items within a given module. Expects owner to
/// invoke `walk_item` on a module item. Ignores nested modules.
pub struct TransItemsWithinModVisitor<'a, 'tcx: 'a> {
    pub ccx: &'a CrateContext<'a, 'tcx>,
}

impl<'a, 'tcx, 'v> Visitor<'v> for TransItemsWithinModVisitor<'a, 'tcx> {
    fn visit_nested_item(&mut self, item_id: hir::ItemId) {
        self.visit_item(self.ccx.tcx().map.expect_item(item_id.id));
    }

    fn visit_item(&mut self, i: &hir::Item) {
        match i.node {
            hir::ItemMod(..) => {
                // skip modules, they will be uncovered by the TransModVisitor
            }
            _ => {
                let def_id = self.ccx.tcx().map.local_def_id(i.id);
                let tcx = self.ccx.tcx();

                // Create a subtask for trans'ing a particular item. We are
                // giving `trans_item` access to this item, so also record a read.
                tcx.dep_graph.with_task(DepNode::TransCrateItem(def_id), || {
                    tcx.dep_graph.read(DepNode::Hir(def_id));

                    // We are going to be accessing various tables
                    // generated by TypeckItemBody; we also assume
                    // that the body passes type check. These tables
                    // are not individually tracked, so just register
                    // a read here.
                    tcx.dep_graph.read(DepNode::TypeckItemBody(def_id));

                    trans_item(self.ccx, i);
                });

                intravisit::walk_item(self, i);
            }
        }
    }
}

fn collect_translation_items<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>) {
    let time_passes = ccx.sess().time_passes();

    let collection_mode = match ccx.sess().opts.debugging_opts.print_trans_items {
        Some(ref s) => {
            let mode_string = s.to_lowercase();
            let mode_string = mode_string.trim();
            if mode_string == "eager" {
                TransItemCollectionMode::Eager
            } else {
                if mode_string != "lazy" {
                    let message = format!("Unknown codegen-item collection mode '{}'. \
                                           Falling back to 'lazy' mode.",
                                           mode_string);
                    ccx.sess().warn(&message);
                }

                TransItemCollectionMode::Lazy
            }
        }
        None => TransItemCollectionMode::Lazy
    };

    let (items, reference_map) = time(time_passes, "translation item collection", || {
        collector::collect_crate_translation_items(&ccx, collection_mode)
    });

    let strategy = if ccx.sess().opts.debugging_opts.incremental.is_some() {
        PartitioningStrategy::PerModule
    } else {
        PartitioningStrategy::FixedUnitCount(ccx.sess().opts.cg.codegen_units)
    };

    let codegen_units = time(time_passes, "codegen unit partitioning", || {
        partitioning::partition(ccx.tcx(),
                                items.iter().cloned(),
                                strategy,
                                &reference_map)
    });

    if ccx.sess().opts.debugging_opts.print_trans_items.is_some() {
        let mut item_to_cgus = HashMap::new();

        for cgu in codegen_units {
            for (trans_item, linkage) in cgu.items {
                item_to_cgus.entry(trans_item)
                            .or_insert(Vec::new())
                            .push((cgu.name.clone(), linkage));
            }
        }

        let mut item_keys: Vec<_> = items
            .iter()
            .map(|i| {
                let mut output = i.to_string(ccx.tcx());
                output.push_str(" @@");
                let mut empty = Vec::new();
                let mut cgus = item_to_cgus.get_mut(i).unwrap_or(&mut empty);
                cgus.as_mut_slice().sort_by_key(|&(ref name, _)| name.clone());
                cgus.dedup();
                for &(ref cgu_name, linkage) in cgus.iter() {
                    output.push_str(" ");
                    output.push_str(&cgu_name[..]);

                    let linkage_abbrev = match linkage {
                        InstantiationMode::Def(llvm::ExternalLinkage) => "External",
                        InstantiationMode::Def(llvm::AvailableExternallyLinkage) => "Available",
                        InstantiationMode::Def(llvm::LinkOnceAnyLinkage) => "OnceAny",
                        InstantiationMode::Def(llvm::LinkOnceODRLinkage) => "OnceODR",
                        InstantiationMode::Def(llvm::WeakAnyLinkage) => "WeakAny",
                        InstantiationMode::Def(llvm::WeakODRLinkage) => "WeakODR",
                        InstantiationMode::Def(llvm::AppendingLinkage) => "Appending",
                        InstantiationMode::Def(llvm::InternalLinkage) => "Internal",
                        InstantiationMode::Def(llvm::PrivateLinkage) => "Private",
                        InstantiationMode::Def(llvm::ExternalWeakLinkage) => "ExternalWeak",
                        InstantiationMode::Def(llvm::CommonLinkage) => "Common",
                        InstantiationMode::Decl => "Declaration",
                    };

                    output.push_str("[");
                    output.push_str(linkage_abbrev);
                    output.push_str("]");
                }
                output
            })
            .collect();

        item_keys.sort();

        for item in item_keys {
            println!("TRANS_ITEM {}", item);
        }

        let mut ccx_map = ccx.translation_items().borrow_mut();

        for cgi in items {
            ccx_map.insert(cgi, TransItemState::PredictedButNotGenerated);
        }
    }
}