[rustc.git] / src / librustc_mir / shim.rs

// Copyright 2016 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.

use rustc::hir;
use rustc::hir::def_id::DefId;
use rustc::infer;
use rustc::mir::*;
use rustc::ty::{self, Ty, TyCtxt, GenericParamDefKind};
use rustc::ty::subst::{Subst, Substs};
use rustc::ty::query::Providers;

use rustc_data_structures::indexed_vec::{IndexVec, Idx};

use rustc_target::spec::abi::Abi;
use syntax::ast;
use syntax_pos::Span;

use std::fmt;
use std::iter;

use transform::{add_moves_for_packed_drops, add_call_guards};
use transform::{remove_noop_landing_pads, no_landing_pads, simplify};
use util::elaborate_drops::{self, DropElaborator, DropStyle, DropFlagMode};
use util::patch::MirPatch;

pub fn provide(providers: &mut Providers) {
    providers.mir_shims = make_shim;
}

fn make_shim<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                       instance: ty::InstanceDef<'tcx>)
                       -> &'tcx Mir<'tcx>
{
    debug!("make_shim({:?})", instance);

    let mut result = match instance {
        ty::InstanceDef::Item(..) =>
            bug!("item {:?} passed to make_shim", instance),
        ty::InstanceDef::FnPtrShim(def_id, ty) => {
            let trait_ = tcx.trait_of_item(def_id).unwrap();
            let adjustment = match tcx.lang_items().fn_trait_kind(trait_) {
                Some(ty::ClosureKind::FnOnce) => Adjustment::Identity,
                Some(ty::ClosureKind::FnMut) |
                Some(ty::ClosureKind::Fn) => Adjustment::Deref,
                None => bug!("fn pointer {:?} is not an fn", ty)
            };
            // HACK: we need the "real" argument types for the MIR,
            // but because our substs are (Self, Args), where Args
            // is a tuple, we must include the *concrete* argument
            // types in the MIR. They will be substituted again with
            // the param-substs, but because they are concrete, this
            // will not do any harm.
            let sig = tcx.erase_late_bound_regions(&ty.fn_sig(tcx));
            let arg_tys = sig.inputs();

            build_call_shim(
                tcx,
                def_id,
                adjustment,
                CallKind::Indirect,
                Some(arg_tys)
            )
        }
        ty::InstanceDef::Virtual(def_id, _) => {
            // We are generating a call back to our def-id, which the
            // codegen backend knows to turn to an actual virtual call.
            build_call_shim(
                tcx,
                def_id,
                Adjustment::Identity,
                CallKind::Direct(def_id),
                None
            )
        }
        ty::InstanceDef::ClosureOnceShim { call_once } => {
            let fn_mut = tcx.lang_items().fn_mut_trait().unwrap();
            let call_mut = tcx.global_tcx()
                .associated_items(fn_mut)
                .find(|it| it.kind == ty::AssociatedKind::Method)
                .unwrap().def_id;

            build_call_shim(
                tcx,
                call_once,
                Adjustment::RefMut,
                CallKind::Direct(call_mut),
                None
            )
        }
        ty::InstanceDef::DropGlue(def_id, ty) => {
            build_drop_shim(tcx, def_id, ty)
        }
        ty::InstanceDef::CloneShim(def_id, ty) => {
            let name = tcx.item_name(def_id);
            if name == "clone" {
                build_clone_shim(tcx, def_id, ty)
            } else if name == "clone_from" {
                debug!("make_shim({:?}: using default trait implementation", instance);
                return tcx.optimized_mir(def_id);
            } else {
                bug!("builtin clone shim {:?} not supported", instance)
            }
        }
        ty::InstanceDef::Intrinsic(_) => {
            bug!("creating shims from intrinsics ({:?}) is unsupported", instance)
        }
    };
    debug!("make_shim({:?}) = untransformed {:?}", instance, result);
    add_moves_for_packed_drops::add_moves_for_packed_drops(
        tcx, &mut result, instance.def_id());
    no_landing_pads::no_landing_pads(tcx, &mut result);
    remove_noop_landing_pads::remove_noop_landing_pads(tcx, &mut result);
    simplify::simplify_cfg(&mut result);
    add_call_guards::CriticalCallEdges.add_call_guards(&mut result);
    debug!("make_shim({:?}) = {:?}", instance, result);

    tcx.alloc_mir(result)
}

#[derive(Copy, Clone, Debug, PartialEq)]
enum Adjustment {
    Identity,
    Deref,
    RefMut,
}

#[derive(Copy, Clone, Debug, PartialEq)]
enum CallKind {
    Indirect,
    Direct(DefId),
}

fn temp_decl(mutability: Mutability, ty: Ty, span: Span) -> LocalDecl {
    let source_info = SourceInfo { scope: OUTERMOST_SOURCE_SCOPE, span };
    LocalDecl {
        mutability, ty,
        user_ty: None,
        name: None,
        source_info,
        visibility_scope: source_info.scope,
        internal: false,
        is_user_variable: None,
    }
}

fn local_decls_for_sig<'tcx>(sig: &ty::FnSig<'tcx>, span: Span)
    -> IndexVec<Local, LocalDecl<'tcx>>
{
    iter::once(temp_decl(Mutability::Mut, sig.output(), span))
        .chain(sig.inputs().iter().map(
            |ity| temp_decl(Mutability::Not, ity, span)))
        .collect()
}

fn build_drop_shim<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                             def_id: DefId,
                             ty: Option<Ty<'tcx>>)
                             -> Mir<'tcx>
{
    debug!("build_drop_shim(def_id={:?}, ty={:?})", def_id, ty);

    // Check if this is a generator, if so, return the drop glue for it
    if let Some(&ty::TyS { sty: ty::Generator(gen_def_id, substs, _), .. }) = ty {
        let mir = &**tcx.optimized_mir(gen_def_id).generator_drop.as_ref().unwrap();
        return mir.subst(tcx, substs.substs);
    }

    let substs = if let Some(ty) = ty {
        tcx.intern_substs(&[ty.into()])
    } else {
        Substs::identity_for_item(tcx, def_id)
    };
    let sig = tcx.fn_sig(def_id).subst(tcx, substs);
    let sig = tcx.erase_late_bound_regions(&sig);
    let span = tcx.def_span(def_id);

    let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };

    let return_block = BasicBlock::new(1);
    let mut blocks = IndexVec::new();
    let block = |blocks: &mut IndexVec<_, _>, kind| {
        blocks.push(BasicBlockData {
            statements: vec![],
            terminator: Some(Terminator { source_info, kind }),
            is_cleanup: false
        })
    };
    block(&mut blocks, TerminatorKind::Goto { target: return_block });
    block(&mut blocks, TerminatorKind::Return);

    let mut mir = Mir::new(
        blocks,
        IndexVec::from_elem_n(
            SourceScopeData { span: span, parent_scope: None }, 1
        ),
        ClearCrossCrate::Clear,
        IndexVec::new(),
        None,
        local_decls_for_sig(&sig, span),
        sig.inputs().len(),
        vec![],
        span
    );

    if let Some(..) = ty {
        let patch = {
            let param_env = tcx.param_env(def_id).with_reveal_all();
            let mut elaborator = DropShimElaborator {
                mir: &mir,
                patch: MirPatch::new(&mir),
                tcx,
                param_env
            };
            let dropee = Place::Local(Local::new(1+0)).deref();
            let resume_block = elaborator.patch.resume_block();
            elaborate_drops::elaborate_drop(
                &mut elaborator,
                source_info,
                &dropee,
                (),
                return_block,
                elaborate_drops::Unwind::To(resume_block),
                START_BLOCK
            );
            elaborator.patch
        };
        patch.apply(&mut mir);
    }

    mir
}

pub struct DropShimElaborator<'a, 'tcx: 'a> {
    pub mir: &'a Mir<'tcx>,
    pub patch: MirPatch<'tcx>,
    pub tcx: TyCtxt<'a, 'tcx, 'tcx>,
    pub param_env: ty::ParamEnv<'tcx>,
}

impl<'a, 'tcx> fmt::Debug for DropShimElaborator<'a, 'tcx> {
    fn fmt(&self, _f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
        Ok(())
    }
}

impl<'a, 'tcx> DropElaborator<'a, 'tcx> for DropShimElaborator<'a, 'tcx> {
    type Path = ();

    fn patch(&mut self) -> &mut MirPatch<'tcx> { &mut self.patch }
    fn mir(&self) -> &'a Mir<'tcx> { self.mir }
    fn tcx(&self) -> TyCtxt<'a, 'tcx, 'tcx> { self.tcx }
    fn param_env(&self) -> ty::ParamEnv<'tcx> { self.param_env }

    fn drop_style(&self, _path: Self::Path, mode: DropFlagMode) -> DropStyle {
        if let DropFlagMode::Shallow = mode {
            DropStyle::Static
        } else {
            DropStyle::Open
        }
    }

    fn get_drop_flag(&mut self, _path: Self::Path) -> Option<Operand<'tcx>> {
        None
    }

    fn clear_drop_flag(&mut self, _location: Location, _path: Self::Path, _mode: DropFlagMode) {
    }

    fn field_subpath(&self, _path: Self::Path, _field: Field) -> Option<Self::Path> {
        None
    }
    fn deref_subpath(&self, _path: Self::Path) -> Option<Self::Path> {
        None
    }
    fn downcast_subpath(&self, _path: Self::Path, _variant: usize) -> Option<Self::Path> {
        Some(())
    }
    fn array_subpath(&self, _path: Self::Path, _index: u32, _size: u32) -> Option<Self::Path> {
        None
    }
}

/// Build a `Clone::clone` shim for `self_ty`. Here, `def_id` is `Clone::clone`.
fn build_clone_shim<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                              def_id: DefId,
                              self_ty: Ty<'tcx>)
                              -> Mir<'tcx>
{
    debug!("build_clone_shim(def_id={:?})", def_id);

    let mut builder = CloneShimBuilder::new(tcx, def_id, self_ty);
    let is_copy = !self_ty.moves_by_default(tcx, tcx.param_env(def_id), builder.span);

    let dest = Place::Local(RETURN_PLACE);
    let src = Place::Local(Local::new(1+0)).deref();

    match self_ty.sty {
        _ if is_copy => builder.copy_shim(),
        ty::Array(ty, len) => {
            let len = len.unwrap_usize(tcx);
            builder.array_shim(dest, src, ty, len)
        }
        ty::Closure(def_id, substs) => {
            builder.tuple_like_shim(
                dest, src,
                substs.upvar_tys(def_id, tcx)
            )
        }
        ty::Tuple(tys) => builder.tuple_like_shim(dest, src, tys.iter().cloned()),
        _ => {
            bug!("clone shim for `{:?}` which is not `Copy` and is not an aggregate", self_ty)
        }
    };

    builder.into_mir()
}

struct CloneShimBuilder<'a, 'tcx: 'a> {
    tcx: TyCtxt<'a, 'tcx, 'tcx>,
    def_id: DefId,
    local_decls: IndexVec<Local, LocalDecl<'tcx>>,
    blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
    span: Span,
    sig: ty::FnSig<'tcx>,
}

impl<'a, 'tcx> CloneShimBuilder<'a, 'tcx> {
    fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>,
           def_id: DefId,
           self_ty: Ty<'tcx>) -> Self {
        // we must subst the self_ty because it's
        // otherwise going to be TySelf and we can't index
        // or access fields of a Place of type TySelf.
        let substs = tcx.mk_substs_trait(self_ty, &[]);
        let sig = tcx.fn_sig(def_id).subst(tcx, substs);
        let sig = tcx.erase_late_bound_regions(&sig);
        let span = tcx.def_span(def_id);

        CloneShimBuilder {
            tcx,
            def_id,
            local_decls: local_decls_for_sig(&sig, span),
            blocks: IndexVec::new(),
            span,
            sig,
        }
    }

    fn into_mir(self) -> Mir<'tcx> {
        Mir::new(
            self.blocks,
            IndexVec::from_elem_n(
                SourceScopeData { span: self.span, parent_scope: None }, 1
            ),
            ClearCrossCrate::Clear,
            IndexVec::new(),
            None,
            self.local_decls,
            self.sig.inputs().len(),
            vec![],
            self.span
        )
    }

    fn source_info(&self) -> SourceInfo {
        SourceInfo { span: self.span, scope: OUTERMOST_SOURCE_SCOPE }
    }

    fn block(
        &mut self,
        statements: Vec<Statement<'tcx>>,
        kind: TerminatorKind<'tcx>,
        is_cleanup: bool
    ) -> BasicBlock {
        let source_info = self.source_info();
        self.blocks.push(BasicBlockData {
            statements,
            terminator: Some(Terminator { source_info, kind }),
            is_cleanup,
        })
    }

    /// Gives the index of an upcoming BasicBlock, with an offset.
    /// offset=0 will give you the index of the next BasicBlock,
    /// offset=1 will give the index of the next-to-next block,
    /// offset=-1 will give you the index of the last-created block
    fn block_index_offset(&mut self, offset: usize) -> BasicBlock {
        BasicBlock::new(self.blocks.len() + offset)
    }

    fn make_statement(&self, kind: StatementKind<'tcx>) -> Statement<'tcx> {
        Statement {
            source_info: self.source_info(),
            kind,
        }
    }

    fn copy_shim(&mut self) {
        let rcvr = Place::Local(Local::new(1+0)).deref();
        let ret_statement = self.make_statement(
            StatementKind::Assign(
                Place::Local(RETURN_PLACE),
                Rvalue::Use(Operand::Copy(rcvr))
            )
        );
        self.block(vec![ret_statement], TerminatorKind::Return, false);
    }

    fn make_place(&mut self, mutability: Mutability, ty: Ty<'tcx>) -> Place<'tcx> {
        let span = self.span;
        Place::Local(
            self.local_decls.push(temp_decl(mutability, ty, span))
        )
    }

    fn make_clone_call(
        &mut self,
        dest: Place<'tcx>,
        src: Place<'tcx>,
        ty: Ty<'tcx>,
        next: BasicBlock,
        cleanup: BasicBlock
    ) {
        let tcx = self.tcx;

        let substs = Substs::for_item(tcx, self.def_id, |param, _| {
            match param.kind {
                GenericParamDefKind::Lifetime => tcx.types.re_erased.into(),
                GenericParamDefKind::Type {..} => ty.into(),
            }
        });

        // `func == Clone::clone(&ty) -> ty`
        let func_ty = tcx.mk_fn_def(self.def_id, substs);
        let func = Operand::Constant(box Constant {
            span: self.span,
            ty: func_ty,
            user_ty: None,
            literal: ty::Const::zero_sized(self.tcx, func_ty),
        });

        let ref_loc = self.make_place(
            Mutability::Not,
            tcx.mk_ref(tcx.types.re_erased, ty::TypeAndMut {
                ty,
                mutbl: hir::Mutability::MutImmutable,
            })
        );

        // `let ref_loc: &ty = &src;`
        let statement = self.make_statement(
            StatementKind::Assign(
                ref_loc.clone(),
                Rvalue::Ref(tcx.types.re_erased, BorrowKind::Shared, src)
            )
        );

        // `let loc = Clone::clone(ref_loc);`
        self.block(vec![statement], TerminatorKind::Call {
            func,
            args: vec![Operand::Move(ref_loc)],
            destination: Some((dest, next)),
            cleanup: Some(cleanup),
        }, false);
    }

    fn loop_header(
        &mut self,
        beg: Place<'tcx>,
        end: Place<'tcx>,
        loop_body: BasicBlock,
        loop_end: BasicBlock,
        is_cleanup: bool
    ) {
        let tcx = self.tcx;

        let cond = self.make_place(Mutability::Mut, tcx.types.bool);
        let compute_cond = self.make_statement(
            StatementKind::Assign(
                cond.clone(),
                Rvalue::BinaryOp(BinOp::Ne, Operand::Copy(end), Operand::Copy(beg))
            )
        );

        // `if end != beg { goto loop_body; } else { goto loop_end; }`
        self.block(
            vec![compute_cond],
            TerminatorKind::if_(tcx, Operand::Move(cond), loop_body, loop_end),
            is_cleanup
        );
    }

    fn make_usize(&self, value: u64) -> Box<Constant<'tcx>> {
        box Constant {
            span: self.span,
            ty: self.tcx.types.usize,
            user_ty: None,
            literal: ty::Const::from_usize(self.tcx, value),
        }
    }

    fn array_shim(&mut self, dest: Place<'tcx>, src: Place<'tcx>, ty: Ty<'tcx>, len: u64) {
        let tcx = self.tcx;
        let span = self.span;

        let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
        let end = self.make_place(Mutability::Not, tcx.types.usize);

        // BB #0
        // `let mut beg = 0;`
        // `let end = len;`
        // `goto #1;`
        let inits = vec![
            self.make_statement(
                StatementKind::Assign(
                    Place::Local(beg),
                    Rvalue::Use(Operand::Constant(self.make_usize(0)))
                )
            ),
            self.make_statement(
                StatementKind::Assign(
                    end.clone(),
                    Rvalue::Use(Operand::Constant(self.make_usize(len)))
                )
            )
        ];
        self.block(inits, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);

        // BB #1: loop {
        //     BB #2;
        //     BB #3;
        // }
        // BB #4;
        self.loop_header(Place::Local(beg), end, BasicBlock::new(2), BasicBlock::new(4), false);

        // BB #2
        // `dest[i] = Clone::clone(src[beg])`;
        // Goto #3 if ok, #5 if unwinding happens.
        let dest_field = dest.clone().index(beg);
        let src_field = src.clone().index(beg);
        self.make_clone_call(dest_field, src_field, ty, BasicBlock::new(3),
                             BasicBlock::new(5));

        // BB #3
        // `beg = beg + 1;`
        // `goto #1`;
        let statements = vec![
            self.make_statement(
                StatementKind::Assign(
                    Place::Local(beg),
                    Rvalue::BinaryOp(
                        BinOp::Add,
                        Operand::Copy(Place::Local(beg)),
                        Operand::Constant(self.make_usize(1))
                    )
                )
            )
        ];
        self.block(statements, TerminatorKind::Goto { target: BasicBlock::new(1) }, false);

        // BB #4
        // `return dest;`
        self.block(vec![], TerminatorKind::Return, false);

        // BB #5 (cleanup)
        // `let end = beg;`
        // `let mut beg = 0;`
        // goto #6;
        let end = beg;
        let beg = self.local_decls.push(temp_decl(Mutability::Mut, tcx.types.usize, span));
        let init = self.make_statement(
            StatementKind::Assign(
                Place::Local(beg),
                Rvalue::Use(Operand::Constant(self.make_usize(0)))
            )
        );
        self.block(vec![init], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);

        // BB #6 (cleanup): loop {
        //     BB #7;
        //     BB #8;
        // }
        // BB #9;
        self.loop_header(Place::Local(beg), Place::Local(end),
                         BasicBlock::new(7), BasicBlock::new(9), true);

        // BB #7 (cleanup)
        // `drop(dest[beg])`;
        self.block(vec![], TerminatorKind::Drop {
            location: dest.index(beg),
            target: BasicBlock::new(8),
            unwind: None,
        }, true);

        // BB #8 (cleanup)
        // `beg = beg + 1;`
        // `goto #6;`
        let statement = self.make_statement(
            StatementKind::Assign(
                Place::Local(beg),
                Rvalue::BinaryOp(
                    BinOp::Add,
                    Operand::Copy(Place::Local(beg)),
                    Operand::Constant(self.make_usize(1))
                )
            )
        );
        self.block(vec![statement], TerminatorKind::Goto { target: BasicBlock::new(6) }, true);

        // BB #9 (resume)
        self.block(vec![], TerminatorKind::Resume, true);
    }

    fn tuple_like_shim<I>(&mut self, dest: Place<'tcx>,
                          src: Place<'tcx>, tys: I)
            where I: Iterator<Item = ty::Ty<'tcx>> {
        let mut previous_field = None;
        for (i, ity) in tys.enumerate() {
            let field = Field::new(i);
            let src_field = src.clone().field(field, ity);

            let dest_field = dest.clone().field(field, ity);

            // #(2i + 1) is the cleanup block for the previous clone operation
            let cleanup_block = self.block_index_offset(1);
            // #(2i + 2) is the next cloning block
            // (or the Return terminator if this is the last block)
            let next_block = self.block_index_offset(2);

            // BB #(2i)
            // `dest.i = Clone::clone(&src.i);`
            // Goto #(2i + 2) if ok, #(2i + 1) if unwinding happens.
            self.make_clone_call(
                dest_field.clone(),
                src_field,
                ity,
                next_block,
                cleanup_block,
            );

            // BB #(2i + 1) (cleanup)
            if let Some((previous_field, previous_cleanup)) = previous_field.take() {
                // Drop previous field and goto previous cleanup block.
                self.block(vec![], TerminatorKind::Drop {
                    location: previous_field,
                    target: previous_cleanup,
                    unwind: None,
                }, true);
            } else {
                // Nothing to drop, just resume.
                self.block(vec![], TerminatorKind::Resume, true);
            }

            previous_field = Some((dest_field, cleanup_block));
        }

        self.block(vec![], TerminatorKind::Return, false);
    }
}

/// Build a "call" shim for `def_id`. The shim calls the
/// function specified by `call_kind`, first adjusting its first
/// argument according to `rcvr_adjustment`.
///
/// If `untuple_args` is a vec of types, the second argument of the
/// function will be untupled as these types.
fn build_call_shim<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                             def_id: DefId,
                             rcvr_adjustment: Adjustment,
                             call_kind: CallKind,
                             untuple_args: Option<&[Ty<'tcx>]>)
                             -> Mir<'tcx>
{
    debug!("build_call_shim(def_id={:?}, rcvr_adjustment={:?}, \
            call_kind={:?}, untuple_args={:?})",
           def_id, rcvr_adjustment, call_kind, untuple_args);

    let sig = tcx.fn_sig(def_id);
    let sig = tcx.erase_late_bound_regions(&sig);
    let span = tcx.def_span(def_id);

    debug!("build_call_shim: sig={:?}", sig);

    let mut local_decls = local_decls_for_sig(&sig, span);
    let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };

    let rcvr_arg = Local::new(1+0);
    let rcvr_l = Place::Local(rcvr_arg);
    let mut statements = vec![];

    let rcvr = match rcvr_adjustment {
        Adjustment::Identity => Operand::Move(rcvr_l),
        Adjustment::Deref => Operand::Copy(rcvr_l.deref()),
        Adjustment::RefMut => {
            // let rcvr = &mut rcvr;
            let ref_rcvr = local_decls.push(temp_decl(
                Mutability::Not,
                tcx.mk_ref(tcx.types.re_erased, ty::TypeAndMut {
                    ty: sig.inputs()[0],
                    mutbl: hir::Mutability::MutMutable
                }),
                span
            ));
            let borrow_kind = BorrowKind::Mut {
                allow_two_phase_borrow: false,
            };
            statements.push(Statement {
                source_info,
                kind: StatementKind::Assign(
                    Place::Local(ref_rcvr),
                    Rvalue::Ref(tcx.types.re_erased, borrow_kind, rcvr_l)
                )
            });
            Operand::Move(Place::Local(ref_rcvr))
        }
    };

    let (callee, mut args) = match call_kind {
        CallKind::Indirect => (rcvr, vec![]),
        CallKind::Direct(def_id) => {
            let ty = tcx.type_of(def_id);
            (Operand::Constant(box Constant {
                span,
                ty,
                user_ty: None,
                literal: ty::Const::zero_sized(tcx, ty),
             }),
             vec![rcvr])
        }
    };

    if let Some(untuple_args) = untuple_args {
        args.extend(untuple_args.iter().enumerate().map(|(i, ity)| {
            let arg_place = Place::Local(Local::new(1+1));
            Operand::Move(arg_place.field(Field::new(i), *ity))
        }));
    } else {
        args.extend((1..sig.inputs().len()).map(|i| {
            Operand::Move(Place::Local(Local::new(1+i)))
        }));
    }

    let mut blocks = IndexVec::new();
    let block = |blocks: &mut IndexVec<_, _>, statements, kind, is_cleanup| {
        blocks.push(BasicBlockData {
            statements,
            terminator: Some(Terminator { source_info, kind }),
            is_cleanup
        })
    };

    // BB #0
    block(&mut blocks, statements, TerminatorKind::Call {
        func: callee,
        args,
        destination: Some((Place::Local(RETURN_PLACE),
                           BasicBlock::new(1))),
        cleanup: if let Adjustment::RefMut = rcvr_adjustment {
            Some(BasicBlock::new(3))
        } else {
            None
        }
    }, false);

    if let Adjustment::RefMut = rcvr_adjustment {
        // BB #1 - drop for Self
        block(&mut blocks, vec![], TerminatorKind::Drop {
            location: Place::Local(rcvr_arg),
            target: BasicBlock::new(2),
            unwind: None
        }, false);
    }
    // BB #1/#2 - return
    block(&mut blocks, vec![], TerminatorKind::Return, false);
    if let Adjustment::RefMut = rcvr_adjustment {
        // BB #3 - drop if closure panics
        block(&mut blocks, vec![], TerminatorKind::Drop {
            location: Place::Local(rcvr_arg),
            target: BasicBlock::new(4),
            unwind: None
        }, true);

        // BB #4 - resume
        block(&mut blocks, vec![], TerminatorKind::Resume, true);
    }

    let mut mir = Mir::new(
        blocks,
        IndexVec::from_elem_n(
            SourceScopeData { span: span, parent_scope: None }, 1
        ),
        ClearCrossCrate::Clear,
        IndexVec::new(),
        None,
        local_decls,
        sig.inputs().len(),
        vec![],
        span
    );
    if let Abi::RustCall = sig.abi {
        mir.spread_arg = Some(Local::new(sig.inputs().len()));
    }
    mir
}

pub fn build_adt_ctor<'a, 'gcx, 'tcx>(infcx: &infer::InferCtxt<'a, 'gcx, 'tcx>,
                                      ctor_id: ast::NodeId,
                                      fields: &[hir::StructField],
                                      span: Span)
                                      -> Mir<'tcx>
{
    let tcx = infcx.tcx;
    let gcx = tcx.global_tcx();
    let def_id = tcx.hir.local_def_id(ctor_id);
    let param_env = gcx.param_env(def_id);

    // Normalize the sig.
    let sig = gcx.fn_sig(def_id).no_late_bound_regions().expect("LBR in ADT constructor signature");
    let sig = gcx.normalize_erasing_regions(param_env, sig);

    let (adt_def, substs) = match sig.output().sty {
        ty::Adt(adt_def, substs) => (adt_def, substs),
        _ => bug!("unexpected type for ADT ctor {:?}", sig.output())
    };

    debug!("build_ctor: def_id={:?} sig={:?} fields={:?}", def_id, sig, fields);

    let local_decls = local_decls_for_sig(&sig, span);

    let source_info = SourceInfo {
        span,
        scope: OUTERMOST_SOURCE_SCOPE
    };

    let variant_no = if adt_def.is_enum() {
        adt_def.variant_index_with_id(def_id)
    } else {
        0
    };

    // return = ADT(arg0, arg1, ...); return
    let start_block = BasicBlockData {
        statements: vec![Statement {
            source_info,
            kind: StatementKind::Assign(
                Place::Local(RETURN_PLACE),
                Rvalue::Aggregate(
                    box AggregateKind::Adt(adt_def, variant_no, substs, None, None),
                    (1..sig.inputs().len()+1).map(|i| {
                        Operand::Move(Place::Local(Local::new(i)))
                    }).collect()
                )
            )
        }],
        terminator: Some(Terminator {
            source_info,
            kind: TerminatorKind::Return,
        }),
        is_cleanup: false
    };

    Mir::new(
        IndexVec::from_elem_n(start_block, 1),
        IndexVec::from_elem_n(
            SourceScopeData { span: span, parent_scope: None }, 1
        ),
        ClearCrossCrate::Clear,
        IndexVec::new(),
        None,
        local_decls,
        sig.inputs().len(),
        vec![],
        span
    )
}