Auto merge of #39648 - Aatch:mir-inlining-2, r=eddyb

[MIR] Implement Inlining

Fairly basic implementation of inlining for MIR. Uses conservative
heuristics for inlining.

Doesn't handle a number of cases, but can be extended later. This is basically the same as the previous inlining PR, but without the span-related changes (as the bugs it was dealing with have since been fixed).

/cc @rust-lang/compiler

src/librustc/mir/mod.rs

@@ -19,6 +19,7 @@ use hir::def::CtorKind;
 use hir::def_id::DefId;
 use ty::subst::Substs;
 use ty::{self, AdtDef, ClosureSubsts, Region, Ty};
+use ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
 use util::ppaux;
 use rustc_back::slice;
 use hir::InlineAsm;
@@ -63,8 +64,7 @@ macro_rules! newtype_index {
 }
 
 /// Lowered representation of a single function.
-// Do not implement clone for Mir, which can be accidently done and kind of expensive.
+#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
-#[derive(RustcEncodable, RustcDecodable, Debug)]
 pub struct Mir<'tcx> {
     /// List of basic blocks. References to basic block use a newtyped index type `BasicBlock`
     /// that indexes into this vector.
@@ -1333,3 +1333,347 @@ impl Location {
         }
     }
 }
+
+
+/*
+ * TypeFoldable implementations for MIR types
+ */
+
+impl<'tcx> TypeFoldable<'tcx> for Mir<'tcx> {
+    fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
+        Mir {
+            basic_blocks: self.basic_blocks.fold_with(folder),
+            visibility_scopes: self.visibility_scopes.clone(),
+            promoted: self.promoted.fold_with(folder),
+            return_ty: self.return_ty.fold_with(folder),
+            local_decls: self.local_decls.fold_with(folder),
+            arg_count: self.arg_count,
+            upvar_decls: self.upvar_decls.clone(),
+            spread_arg: self.spread_arg,
+            span: self.span,
+            cache: cache::Cache::new()
+        }
+    }
+
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
+        self.basic_blocks.visit_with(visitor) ||
+        self.promoted.visit_with(visitor)     ||
+        self.return_ty.visit_with(visitor)    ||
+        self.local_decls.visit_with(visitor)
+    }
+}
+
+impl<'tcx> TypeFoldable<'tcx> for LocalDecl<'tcx> {
+    fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
+        LocalDecl {
+            ty: self.ty.fold_with(folder),
+            ..self.clone()
+        }
+    }
+
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
+        self.ty.visit_with(visitor)
+    }
+}
+
+impl<'tcx> TypeFoldable<'tcx> for BasicBlockData<'tcx> {
+    fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
+        BasicBlockData {
+            statements: self.statements.fold_with(folder),
+            terminator: self.terminator.fold_with(folder),
+            is_cleanup: self.is_cleanup
+        }
+    }
+
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
+        self.statements.visit_with(visitor) || self.terminator.visit_with(visitor)
+    }
+}
+
+impl<'tcx> TypeFoldable<'tcx> for Statement<'tcx> {
+    fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
+        use mir::StatementKind::*;
+
+        let kind = match self.kind {
+            Assign(ref lval, ref rval) => Assign(lval.fold_with(folder), rval.fold_with(folder)),
+            SetDiscriminant { ref lvalue, variant_index } => SetDiscriminant {
+                lvalue: lvalue.fold_with(folder),
+                variant_index: variant_index
+            },
+            StorageLive(ref lval) => StorageLive(lval.fold_with(folder)),
+            StorageDead(ref lval) => StorageDead(lval.fold_with(folder)),
+            InlineAsm { ref asm, ref outputs, ref inputs } => InlineAsm {
+                asm: asm.clone(),
+                outputs: outputs.fold_with(folder),
+                inputs: inputs.fold_with(folder)
+            },
+            Nop => Nop,
+        };
+        Statement {
+            source_info: self.source_info,
+            kind: kind
+        }
+    }
+
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
+        use mir::StatementKind::*;
+
+        match self.kind {
+            Assign(ref lval, ref rval) => { lval.visit_with(visitor) || rval.visit_with(visitor) }
+            SetDiscriminant { ref lvalue, .. } |
+            StorageLive(ref lvalue) |
+            StorageDead(ref lvalue) => lvalue.visit_with(visitor),
+            InlineAsm { ref outputs, ref inputs, .. } =>
+                outputs.visit_with(visitor) || inputs.visit_with(visitor),
+            Nop => false,
+        }
+    }
+}
+
+impl<'tcx> TypeFoldable<'tcx> for Terminator<'tcx> {
+    fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
+        use mir::TerminatorKind::*;
+
+        let kind = match self.kind {
+            Goto { target } => Goto { target: target },
+            SwitchInt { ref discr, switch_ty, ref values, ref targets } => SwitchInt {
+                discr: discr.fold_with(folder),
+                switch_ty: switch_ty.fold_with(folder),
+                values: values.clone(),
+                targets: targets.clone()
+            },
+            Drop { ref location, target, unwind } => Drop {
+                location: location.fold_with(folder),
+                target: target,
+                unwind: unwind
+            },
+            DropAndReplace { ref location, ref value, target, unwind } => DropAndReplace {
+                location: location.fold_with(folder),
+                value: value.fold_with(folder),
+                target: target,
+                unwind: unwind
+            },
+            Call { ref func, ref args, ref destination, cleanup } => {
+                let dest = destination.as_ref().map(|&(ref loc, dest)| {
+                    (loc.fold_with(folder), dest)
+                });
+
+                Call {
+                    func: func.fold_with(folder),
+                    args: args.fold_with(folder),
+                    destination: dest,
+                    cleanup: cleanup
+                }
+            },
+            Assert { ref cond, expected, ref msg, target, cleanup } => {
+                let msg = if let AssertMessage::BoundsCheck { ref len, ref index } = *msg {
+                    AssertMessage::BoundsCheck {
+                        len: len.fold_with(folder),
+                        index: index.fold_with(folder),
+                    }
+                } else {
+                    msg.clone()
+                };
+                Assert {
+                    cond: cond.fold_with(folder),
+                    expected: expected,
+                    msg: msg,
+                    target: target,
+                    cleanup: cleanup
+                }
+            },
+            Resume => Resume,
+            Return => Return,
+            Unreachable => Unreachable,
+        };
+        Terminator {
+            source_info: self.source_info,
+            kind: kind
+        }
+    }
+
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
+        use mir::TerminatorKind::*;
+
+        match self.kind {
+            SwitchInt { ref discr, switch_ty, .. } =>
+                discr.visit_with(visitor) || switch_ty.visit_with(visitor),
+            Drop { ref location, ..} => location.visit_with(visitor),
+            DropAndReplace { ref location, ref value, ..} =>
+                location.visit_with(visitor) || value.visit_with(visitor),
+            Call { ref func, ref args, ref destination, .. } => {
+                let dest = if let Some((ref loc, _)) = *destination {
+                    loc.visit_with(visitor)
+                } else { false };
+                dest || func.visit_with(visitor) || args.visit_with(visitor)
+            },
+            Assert { ref cond, ref msg, .. } => {
+                if cond.visit_with(visitor) {
+                    if let AssertMessage::BoundsCheck { ref len, ref index } = *msg {
+                        len.visit_with(visitor) || index.visit_with(visitor)
+                    } else {
+                        false
+                    }
+                } else {
+                    false
+                }
+            },
+            Goto { .. } |
+            Resume |
+            Return |
+            Unreachable => false
+        }
+    }
+}
+
+impl<'tcx> TypeFoldable<'tcx> for Lvalue<'tcx> {
+    fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
+        match self {
+            &Lvalue::Projection(ref p) => Lvalue::Projection(p.fold_with(folder)),
+            _ => self.clone()
+        }
+    }
+
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
+        if let &Lvalue::Projection(ref p) = self {
+            p.visit_with(visitor)
+        } else {
+            false
+        }
+    }
+}
+
+impl<'tcx> TypeFoldable<'tcx> for Rvalue<'tcx> {
+    fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
+        use mir::Rvalue::*;
+        match *self {
+            Use(ref op) => Use(op.fold_with(folder)),
+            Repeat(ref op, len) => Repeat(op.fold_with(folder), len),
+            Ref(region, bk, ref lval) => Ref(region.fold_with(folder), bk, lval.fold_with(folder)),
+            Len(ref lval) => Len(lval.fold_with(folder)),
+            Cast(kind, ref op, ty) => Cast(kind, op.fold_with(folder), ty.fold_with(folder)),
+            BinaryOp(op, ref rhs, ref lhs) =>
+                BinaryOp(op, rhs.fold_with(folder), lhs.fold_with(folder)),
+            CheckedBinaryOp(op, ref rhs, ref lhs) =>
+                CheckedBinaryOp(op, rhs.fold_with(folder), lhs.fold_with(folder)),
+            UnaryOp(op, ref val) => UnaryOp(op, val.fold_with(folder)),
+            Discriminant(ref lval) => Discriminant(lval.fold_with(folder)),
+            Box(ty) => Box(ty.fold_with(folder)),
+            Aggregate(ref kind, ref fields) => {
+                let kind = match *kind {
+                    AggregateKind::Array(ty) => AggregateKind::Array(ty.fold_with(folder)),
+                    AggregateKind::Tuple => AggregateKind::Tuple,
+                    AggregateKind::Adt(def, v, substs, n) =>
+                        AggregateKind::Adt(def, v, substs.fold_with(folder), n),
+                    AggregateKind::Closure(id, substs) =>
+                        AggregateKind::Closure(id, substs.fold_with(folder))
+                };
+                Aggregate(kind, fields.fold_with(folder))
+            }
+        }
+    }
+
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
+        use mir::Rvalue::*;
+        match *self {
+            Use(ref op) => op.visit_with(visitor),
+            Repeat(ref op, _) => op.visit_with(visitor),
+            Ref(region, _, ref lval) => region.visit_with(visitor) || lval.visit_with(visitor),
+            Len(ref lval) => lval.visit_with(visitor),
+            Cast(_, ref op, ty) => op.visit_with(visitor) || ty.visit_with(visitor),
+            BinaryOp(_, ref rhs, ref lhs) |
+            CheckedBinaryOp(_, ref rhs, ref lhs) =>
+                rhs.visit_with(visitor) || lhs.visit_with(visitor),
+            UnaryOp(_, ref val) => val.visit_with(visitor),
+            Discriminant(ref lval) => lval.visit_with(visitor),
+            Box(ty) => ty.visit_with(visitor),
+            Aggregate(ref kind, ref fields) => {
+                (match *kind {
+                    AggregateKind::Array(ty) => ty.visit_with(visitor),
+                    AggregateKind::Tuple => false,
+                    AggregateKind::Adt(_, _, substs, _) => substs.visit_with(visitor),
+                    AggregateKind::Closure(_, substs) => substs.visit_with(visitor)
+                }) || fields.visit_with(visitor)
+            }
+        }
+    }
+}
+
+impl<'tcx> TypeFoldable<'tcx> for Operand<'tcx> {
+    fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
+        match *self {
+            Operand::Consume(ref lval) => Operand::Consume(lval.fold_with(folder)),
+            Operand::Constant(ref c) => Operand::Constant(c.fold_with(folder)),
+        }
+    }
+
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
+        match *self {
+            Operand::Consume(ref lval) => lval.visit_with(visitor),
+            Operand::Constant(ref c) => c.visit_with(visitor)
+        }
+    }
+}
+
+impl<'tcx, B, V> TypeFoldable<'tcx> for Projection<'tcx, B, V>
+    where B: TypeFoldable<'tcx>, V: TypeFoldable<'tcx>
+{
+    fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
+        use mir::ProjectionElem::*;
+
+        let base = self.base.fold_with(folder);
+        let elem = match self.elem {
+            Deref => Deref,
+            Field(f, ty) => Field(f, ty.fold_with(folder)),
+            Index(ref v) => Index(v.fold_with(folder)),
+            ref elem => elem.clone()
+        };
+
+        Projection {
+            base: base,
+            elem: elem
+        }
+    }
+
+    fn super_visit_with<Vs: TypeVisitor<'tcx>>(&self, visitor: &mut Vs) -> bool {
+        use mir::ProjectionElem::*;
+
+        self.base.visit_with(visitor) ||
+            match self.elem {
+                Field(_, ty) => ty.visit_with(visitor),
+                Index(ref v) => v.visit_with(visitor),
+                _ => false
+            }
+    }
+}
+
+impl<'tcx> TypeFoldable<'tcx> for Constant<'tcx> {
+    fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
+        Constant {
+            span: self.span.clone(),
+            ty: self.ty.fold_with(folder),
+            literal: self.literal.fold_with(folder)
+        }
+    }
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
+        self.ty.visit_with(visitor) || self.literal.visit_with(visitor)
+    }
+}
+
+impl<'tcx> TypeFoldable<'tcx> for Literal<'tcx> {
+    fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
+        match *self {
+            Literal::Item { def_id, substs } => Literal::Item {
+                def_id: def_id,
+                substs: substs.fold_with(folder)
+            },
+            _ => self.clone()
+        }
+    }
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
+        match *self {
+            Literal::Item { substs, .. } => substs.visit_with(visitor),
+            _ => false
+        }
+    }
+}

src/librustc/ty/mod.rs

@@ -2302,6 +2302,20 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         queries::mir::get(self, DUMMY_SP, did).borrow()
     }
 
+    /// Given the DefId of an item, returns its MIR, borrowed immutably.
+    /// Returns None if there is no MIR for the DefId
+    pub fn maybe_item_mir(self, did: DefId) -> Option<Ref<'gcx, Mir<'gcx>>> {
+        if did.is_local() && !self.maps.mir.borrow().contains_key(&did) {
+            return None;
+        }
+
+        if !did.is_local() && !self.sess.cstore.is_item_mir_available(did) {
+            return None;
+        }
+
+        Some(self.item_mir(did))
+    }
+
     /// If `type_needs_drop` returns true, then `ty` is definitely
     /// non-copy and *might* have a destructor attached; if it returns
     /// false, then `ty` definitely has no destructor (i.e. no drop glue).

src/librustc/ty/structural_impls.rs

@@ -12,6 +12,7 @@ use infer::type_variable;
 use ty::{self, Lift, Ty, TyCtxt};
 use ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
 use rustc_data_structures::accumulate_vec::AccumulateVec;
+use rustc_data_structures::indexed_vec::{IndexVec, Idx};
 
 use std::rc::Rc;
 use syntax::abi;
@@ -834,3 +835,13 @@ impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for ty::error::ExpectedFoun
         self.expected.visit_with(visitor) || self.found.visit_with(visitor)
     }
 }
+
+impl<'tcx, T: TypeFoldable<'tcx>, I: Idx> TypeFoldable<'tcx> for IndexVec<I, T> {
+    fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
+        self.iter().map(|x| x.fold_with(folder)).collect()
+    }
+
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
+        self.iter().any(|t| t.visit_with(visitor))
+    }
+}

src/librustc/ty/util.rs

@@ -654,11 +654,12 @@ impl<'a, 'tcx> ty::TyS<'tcx> {
         }
 
         tcx.layout_depth.set(depth+1);
-        let layout = Layout::compute_uncached(self, infcx)?;
+        let layout = Layout::compute_uncached(self, infcx);
+        tcx.layout_depth.set(depth);
+        let layout = layout?;
         if can_cache {
             tcx.layout_cache.borrow_mut().insert(self, layout);
         }
-        tcx.layout_depth.set(depth);
         Ok(layout)
     }
 

src/librustc_data_structures/indexed_vec.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use std::collections::range::RangeArgument;
 use std::fmt::Debug;
 use std::iter::{self, FromIterator};
 use std::slice;
@@ -145,6 +146,18 @@ impl<I: Idx, T> IndexVec<I, T> {
         self.raw.iter_mut().enumerate().map(IntoIdx { _marker: PhantomData })
     }
 
+    #[inline]
+    pub fn drain<'a, R: RangeArgument<usize>>(
+        &'a mut self, range: R) -> impl Iterator<Item=T> + 'a {
+        self.raw.drain(range)
+    }
+
+    #[inline]
+    pub fn drain_enumerated<'a, R: RangeArgument<usize>>(
+        &'a mut self, range: R) -> impl Iterator<Item=(I, T)> + 'a {
+        self.raw.drain(range).enumerate().map(IntoIdx { _marker: PhantomData })
+    }
+
     #[inline]
     pub fn last(&self) -> Option<I> {
         self.len().checked_sub(1).map(I::new)
@@ -164,6 +177,16 @@ impl<I: Idx, T> IndexVec<I, T> {
     pub fn truncate(&mut self, a: usize) {
         self.raw.truncate(a)
     }
+
+    #[inline]
+    pub fn get(&self, index: I) -> Option<&T> {
+        self.raw.get(index.index())
+    }
+
+    #[inline]
+    pub fn get_mut(&mut self, index: I) -> Option<&mut T> {
+        self.raw.get_mut(index.index())
+    }
 }
 
 impl<I: Idx, T> Index<I> for IndexVec<I, T> {

src/librustc_data_structures/lib.rs

@@ -38,6 +38,7 @@
 #![feature(associated_consts)]
 #![feature(unsize)]
 #![feature(i128_type)]
+#![feature(conservative_impl_trait)]
 
 #![cfg_attr(unix, feature(libc))]
 #![cfg_attr(test, feature(test))]

src/librustc_driver/driver.rs

@@ -1051,6 +1051,7 @@ pub fn phase_4_translate_to_llvm<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
         passes.push_pass(box mir::transform::simplify::SimplifyCfg::new("elaborate-drops"));
 
         // No lifetime analysis based on borrowing can be done from here on out.
+        passes.push_pass(box mir::transform::inline::Inline);
         passes.push_pass(box mir::transform::instcombine::InstCombine::new());
         passes.push_pass(box mir::transform::deaggregator::Deaggregator);
         passes.push_pass(box mir::transform::copy_prop::CopyPropagation);

src/librustc_mir/callgraph.rs

@@ -0,0 +1,252 @@
+// 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.
+
+//! MIR-based callgraph.
+//!
+//! This only considers direct calls
+
+use rustc::hir::def_id::DefId;
+use rustc_data_structures::graph;
+
+use rustc::mir::*;
+use rustc::mir::visit::*;
+
+use rustc::ty;
+
+use rustc::util::nodemap::DefIdMap;
+
+pub struct CallGraph {
+    node_map: DefIdMap<graph::NodeIndex>,
+    graph: graph::Graph<DefId, ()>
+}
+
+impl CallGraph {
+    // FIXME: allow for construction of a callgraph that inspects
+    // cross-crate MIRs if available.
+    pub fn build<'a, 'tcx>(tcx: ty::TyCtxt<'a, 'tcx, 'tcx>) -> CallGraph {
+        let def_ids = tcx.maps.mir.borrow().keys();
+
+        let mut callgraph = CallGraph {
+            node_map: DefIdMap(),
+            graph: graph::Graph::new()
+        };
+
+        for def_id in def_ids {
+            if !def_id.is_local() { continue; }
+
+            let idx = callgraph.add_node(def_id);
+
+            let mut call_visitor = CallVisitor {
+                caller: idx,
+                graph: &mut callgraph
+            };
+
+            let mir = tcx.item_mir(def_id);
+            call_visitor.visit_mir(&mir);
+        }
+
+        callgraph
+    }
+
+    // Iterate over the strongly-connected components of the graph
+    pub fn scc_iter(&self) -> SCCIterator {
+        SCCIterator::new(&self.graph)
+    }
+
+    // Get the def_id for the given graph node
+    pub fn def_id(&self, node: graph::NodeIndex) -> DefId {
+        *self.graph.node_data(node)
+    }
+
+    fn add_node(&mut self, id: DefId) -> graph::NodeIndex {
+        let graph = &mut self.graph;
+        *self.node_map.entry(id).or_insert_with(|| {
+            graph.add_node(id)
+        })
+    }
+}
+
+struct CallVisitor<'a> {
+    caller: graph::NodeIndex,
+    graph: &'a mut CallGraph
+}
+
+impl<'a, 'tcx> Visitor<'tcx> for CallVisitor<'a> {
+    fn visit_terminator_kind(&mut self, _block: BasicBlock,
+                             kind: &TerminatorKind<'tcx>, _loc: Location) {
+        if let TerminatorKind::Call {
+            func: Operand::Constant(ref f)
+            , .. } = *kind {
+            if let ty::TyFnDef(def_id, _, _) = f.ty.sty {
+                let callee = self.graph.add_node(def_id);
+                self.graph.graph.add_edge(self.caller, callee, ());
+            }
+        }
+    }
+}
+
+struct StackElement<'g> {
+    node: graph::NodeIndex,
+    lowlink: usize,
+    children: graph::AdjacentTargets<'g, DefId, ()>
+}
+
+/**
+ * Iterator over strongly-connected-components using Tarjan's algorithm[1]
+ *
+ * [1]: https://en.wikipedia.org/wiki/Tarjan%27s_strongly_connected_components_algorithm
+ */
+pub struct SCCIterator<'g> {
+    graph: &'g graph::Graph<DefId, ()>,
+    index: usize,
+    node_indices: Vec<Option<usize>>,
+    scc_stack: Vec<graph::NodeIndex>,
+    current_scc: Vec<graph::NodeIndex>,
+    visit_stack: Vec<StackElement<'g>>,
+}
+
+impl<'g> SCCIterator<'g> {
+    pub fn new(graph: &'g graph::Graph<DefId, ()>) -> SCCIterator<'g> {
+        if graph.len_nodes() == 0 {
+            return SCCIterator {
+                graph: graph,
+                index: 0,
+                node_indices: Vec::new(),
+                scc_stack: Vec::new(),
+                current_scc: Vec::new(),
+                visit_stack: Vec::new()
+            };
+        }
+
+        let first = graph::NodeIndex(0);
+
+        SCCIterator::with_entry(graph, first)
+    }
+
+    pub fn with_entry(graph: &'g graph::Graph<DefId, ()>,
+                      entry: graph::NodeIndex) -> SCCIterator<'g> {
+        let mut iter = SCCIterator {
+            graph: graph,
+            index: 0,
+            node_indices: Vec::with_capacity(graph.len_nodes()),
+            scc_stack: Vec::new(),
+            current_scc: Vec::new(),
+            visit_stack: Vec::new()
+        };
+
+        iter.visit_one(entry);
+
+        iter
+    }
+
+    fn get_next(&mut self) {
+        self.current_scc.clear();
+
+        while !self.visit_stack.is_empty() {
+            self.visit_children();
+
+            let node = self.visit_stack.pop().unwrap();
+
+            if let Some(last) = self.visit_stack.last_mut() {
+                if last.lowlink > node.lowlink {
+                    last.lowlink = node.lowlink;
+                }
+            }
+
+            debug!("TarjanSCC: Popped node {:?} : lowlink = {:?}; index = {:?}",
+                   node.node, node.lowlink, self.node_index(node.node).unwrap());
+
+            if node.lowlink != self.node_index(node.node).unwrap() {
+                continue;
+            }
+
+            loop {
+                let n = self.scc_stack.pop().unwrap();
+                self.current_scc.push(n);
+                self.set_node_index(n, !0);
+                if n == node.node { return; }
+            }
+        }
+    }
+
+    fn visit_one(&mut self, node: graph::NodeIndex) {
+        self.index += 1;
+        let idx =  self.index;
+        self.set_node_index(node, idx);
+        self.scc_stack.push(node);
+        self.visit_stack.push(StackElement {
+            node: node,
+            lowlink: self.index,
+            children: self.graph.successor_nodes(node)
+        });
+        debug!("TarjanSCC: Node {:?} : index = {:?}", node, idx);
+    }
+
+    fn visit_children(&mut self) {
+        while let Some(child) = self.visit_stack.last_mut().unwrap().children.next() {
+            if let Some(child_num) = self.node_index(child) {
+                let cur = self.visit_stack.last_mut().unwrap();
+                if cur.lowlink > child_num {
+                    cur.lowlink = child_num;
+                }
+            } else {
+                self.visit_one(child);
+            }
+        }
+    }
+
+    fn node_index(&self, node: graph::NodeIndex) -> Option<usize> {
+        self.node_indices.get(node.node_id()).and_then(|&idx| idx)
+    }
+
+    fn set_node_index(&mut self, node: graph::NodeIndex, idx: usize) {
+        let i = node.node_id();
+        if i >= self.node_indices.len() {
+            self.node_indices.resize(i + 1, None);
+        }
+        self.node_indices[i] = Some(idx);
+    }
+}
+
+impl<'g> Iterator for SCCIterator<'g> {
+    type Item = Vec<graph::NodeIndex>;
+
+    fn next(&mut self) -> Option<Vec<graph::NodeIndex>> {
+        self.get_next();
+
+        if self.current_scc.is_empty() {
+            // Try a new root for the next SCC, if the node_indices
+            // map is doesn't contain all nodes, use the smallest one
+            // with no entry, otherwise find the first empty node.
+            //
+            // FIXME: This should probably use a set of precomputed
+            // roots instead
+            if self.node_indices.len() < self.graph.len_nodes() {
+                let idx = graph::NodeIndex(self.node_indices.len());
+                self.visit_one(idx);
+            } else {
+                for idx in 0..self.node_indices.len() {
+                    if self.node_indices[idx].is_none() {
+                        let idx = graph::NodeIndex(idx);
+                        self.visit_one(idx);
+                        break;
+                    }
+                }
+            }
+            self.get_next();
+        }
+
+        if self.current_scc.is_empty() {
+            None
+        } else {
+            Some(self.current_scc.clone())
+        }
+    }
+}

src/librustc_mir/lib.rs

@@ -46,6 +46,7 @@ extern crate rustc_const_eval;
 pub mod diagnostics;
 
 pub mod build;
+pub mod callgraph;
 pub mod def_use;
 pub mod graphviz;
 mod hair;

src/librustc_mir/transform/inline.rs

@@ -0,0 +1,836 @@
+// 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.
+
+//! Inlining pass for MIR functions
+
+use rustc::hir::def_id::DefId;
+
+use rustc_data_structures::bitvec::BitVector;
+use rustc_data_structures::indexed_vec::{Idx, IndexVec};
+use rustc_data_structures::graph;
+
+use rustc::dep_graph::DepNode;
+use rustc::mir::*;
+use rustc::mir::transform::{MirMapPass, MirPassHook, MirSource, Pass};
+use rustc::mir::visit::*;
+use rustc::traits;
+use rustc::ty::{self, Ty, TyCtxt};
+use rustc::ty::subst::{Subst,Substs};
+use rustc::util::nodemap::{DefIdSet};
+
+use super::simplify::{remove_dead_blocks, CfgSimplifier};
+
+use syntax::{attr};
+use syntax::abi::Abi;
+
+use callgraph;
+
+const DEFAULT_THRESHOLD: usize = 50;
+const HINT_THRESHOLD: usize = 100;
+
+const INSTR_COST: usize = 5;
+const CALL_PENALTY: usize = 25;
+
+const UNKNOWN_SIZE_COST: usize = 10;
+
+pub struct Inline;
+
+impl<'tcx> MirMapPass<'tcx> for Inline {
+    fn run_pass<'a>(
+        &mut self,
+        tcx: TyCtxt<'a, 'tcx, 'tcx>,
+        hooks: &mut [Box<for<'s> MirPassHook<'s>>]) {
+
+        if tcx.sess.opts.debugging_opts.mir_opt_level < 2 { return; }
+
+        let _ignore = tcx.dep_graph.in_ignore();
+
+        let callgraph = callgraph::CallGraph::build(tcx);
+
+        let mut inliner = Inliner {
+            tcx: tcx,
+        };
+
+        let def_ids = tcx.maps.mir.borrow().keys();
+        for &def_id in &def_ids {
+            if !def_id.is_local() { continue; }
+
+            let _task = tcx.dep_graph.in_task(DepNode::Mir(def_id));
+            let mut mir = if let Some(mir) = tcx.maps.mir.borrow().get(&def_id) {
+                mir.borrow_mut()
+            } else {
+                continue;
+            };
+
+            tcx.dep_graph.write(DepNode::Mir(def_id));
+
+            let id = tcx.hir.as_local_node_id(def_id).unwrap();
+            let src = MirSource::from_node(tcx, id);
+
+            for hook in &mut *hooks {
+                hook.on_mir_pass(tcx, src, &mut mir, self, false);
+            }
+        }
+
+        for scc in callgraph.scc_iter() {
+            inliner.inline_scc(&callgraph, &scc);
+        }
+
+        for def_id in def_ids {
+            if !def_id.is_local() { continue; }
+
+            let _task = tcx.dep_graph.in_task(DepNode::Mir(def_id));
+            let mut mir = tcx.maps.mir.borrow()[&def_id].borrow_mut();
+            tcx.dep_graph.write(DepNode::Mir(def_id));
+
+            let id = tcx.hir.as_local_node_id(def_id).unwrap();
+            let src = MirSource::from_node(tcx, id);
+
+            for hook in &mut *hooks {
+                hook.on_mir_pass(tcx, src, &mut mir, self, true);
+            }
+        }
+    }
+}
+
+impl<'tcx> Pass for Inline { }
+
+struct Inliner<'a, 'tcx: 'a> {
+    tcx: TyCtxt<'a, 'tcx, 'tcx>,
+}
+
+#[derive(Copy, Clone)]
+struct CallSite<'tcx> {
+    caller: DefId,
+    callee: DefId,
+    substs: &'tcx Substs<'tcx>,
+    bb: BasicBlock,
+    location: SourceInfo,
+}
+
+impl<'a, 'tcx> Inliner<'a, 'tcx> {
+    fn inline_scc(&mut self, callgraph: &callgraph::CallGraph, scc: &[graph::NodeIndex]) -> bool {
+        let mut callsites = Vec::new();
+        let mut in_scc = DefIdSet();
+
+        let mut inlined_into = DefIdSet();
+
+        for &node in scc {
+            let def_id = callgraph.def_id(node);
+
+            // Don't inspect functions from other crates
+            let id = if let Some(id) = self.tcx.hir.as_local_node_id(def_id) {
+                id
+            } else {
+                continue;
+            };
+            let src = MirSource::from_node(self.tcx, id);
+            if let MirSource::Fn(_) = src {
+                if let Some(mir) = self.tcx.maybe_item_mir(def_id) {
+                    for (bb, bb_data) in mir.basic_blocks().iter_enumerated() {
+                        // Don't inline calls that are in cleanup blocks.
+                        if bb_data.is_cleanup { continue; }
+
+                        // Only consider direct calls to functions
+                        let terminator = bb_data.terminator();
+                        if let TerminatorKind::Call {
+                            func: Operand::Constant(ref f), .. } = terminator.kind {
+                            if let ty::TyFnDef(callee_def_id, substs, _) = f.ty.sty {
+                                callsites.push(CallSite {
+                                    caller: def_id,
+                                    callee: callee_def_id,
+                                    substs: substs,
+                                    bb: bb,
+                                    location: terminator.source_info
+                                });
+                            }
+                        }
+                    }
+
+                    in_scc.insert(def_id);
+                }
+            }
+        }
+
+        // Move callsites that are in the the SCC to the end so
+        // they're inlined after calls to outside the SCC
+        let mut first_call_in_scc = callsites.len();
+
+        let mut i = 0;
+        while i < first_call_in_scc {
+            let f = callsites[i].caller;
+            if in_scc.contains(&f) {
+                first_call_in_scc -= 1;
+                callsites.swap(i, first_call_in_scc);
+            } else {
+                i += 1;
+            }
+        }
+
+        let mut local_change;
+        let mut changed = false;
+
+        loop {
+            local_change = false;
+            let mut csi = 0;
+            while csi < callsites.len() {
+                let callsite = callsites[csi];
+                csi += 1;
+
+                let _task = self.tcx.dep_graph.in_task(DepNode::Mir(callsite.caller));
+                self.tcx.dep_graph.write(DepNode::Mir(callsite.caller));
+
+                let callee_mir = {
+                    if let Some(callee_mir) = self.tcx.maybe_item_mir(callsite.callee) {
+                        if !self.should_inline(callsite, &callee_mir) {
+                            continue;
+                        }
+
+                        callee_mir.subst(self.tcx, callsite.substs)
+                    } else {
+                        continue;
+                    }
+
+                };
+
+                let mut caller_mir = {
+                    let map = self.tcx.maps.mir.borrow();
+                    let mir = map.get(&callsite.caller).unwrap();
+                    mir.borrow_mut()
+                };
+
+                let start = caller_mir.basic_blocks().len();
+
+                if !self.inline_call(callsite, &mut caller_mir, callee_mir) {
+                    continue;
+                }
+
+                inlined_into.insert(callsite.caller);
+
+                // Add callsites from inlined function
+                for (bb, bb_data) in caller_mir.basic_blocks().iter_enumerated().skip(start) {
+                    // Only consider direct calls to functions
+                    let terminator = bb_data.terminator();
+                    if let TerminatorKind::Call {
+                        func: Operand::Constant(ref f), .. } = terminator.kind {
+                        if let ty::TyFnDef(callee_def_id, substs, _) = f.ty.sty {
+                            // Don't inline the same function multiple times.
+                            if callsite.callee != callee_def_id {
+                                callsites.push(CallSite {
+                                    caller: callsite.caller,
+                                    callee: callee_def_id,
+                                    substs: substs,
+                                    bb: bb,
+                                    location: terminator.source_info
+                                });
+                            }
+                        }
+                    }
+                }
+
+                csi -= 1;
+                if scc.len() == 1 {
+                    callsites.swap_remove(csi);
+                } else {
+                    callsites.remove(csi);
+                }
+
+                local_change = true;
+                changed = true;
+            }
+
+            if !local_change {
+                break;
+            }
+        }
+
+        // Simplify functions we inlined into.
+        for def_id in inlined_into {
+            let _task = self.tcx.dep_graph.in_task(DepNode::Mir(def_id));
+            self.tcx.dep_graph.write(DepNode::Mir(def_id));
+
+            let mut caller_mir = {
+                let map = self.tcx.maps.mir.borrow();
+                let mir = map.get(&def_id).unwrap();
+                mir.borrow_mut()
+            };
+
+            debug!("Running simplify cfg on {:?}", def_id);
+            CfgSimplifier::new(&mut caller_mir).simplify();
+            remove_dead_blocks(&mut caller_mir);
+        }
+        changed
+    }
+
+    fn should_inline(&self, callsite: CallSite<'tcx>,
+                     callee_mir: &'a Mir<'tcx>) -> bool {
+
+        let tcx = self.tcx;
+
+        // Don't inline closures that have captures
+        // FIXME: Handle closures better
+        if callee_mir.upvar_decls.len() > 0 {
+            return false;
+        }
+
+
+        let attrs = tcx.get_attrs(callsite.callee);
+        let hint = attr::find_inline_attr(None, &attrs[..]);
+
+        let hinted = match hint {
+            // Just treat inline(always) as a hint for now,
+            // there are cases that prevent inlining that we
+            // need to check for first.
+            attr::InlineAttr::Always => true,
+            attr::InlineAttr::Never => return false,
+            attr::InlineAttr::Hint => true,
+            attr::InlineAttr::None => false,
+        };
+
+        // Only inline local functions if they would be eligible for cross-crate
+        // inlining. This is to ensure that the final crate doesn't have MIR that
+        // reference unexported symbols
+        if callsite.callee.is_local() {
+            if callsite.substs.types().count() == 0 && !hinted {
+                return false;
+            }
+        }
+
+        let mut threshold = if hinted {
+            HINT_THRESHOLD
+        } else {
+            DEFAULT_THRESHOLD
+        };
+
+        // Significantly lower the threshold for inlining cold functions
+        if attr::contains_name(&attrs[..], "cold") {
+            threshold /= 5;
+        }
+
+        // Give a bonus functions with a small number of blocks,
+        // We normally have two or three blocks for even
+        // very small functions.
+        if callee_mir.basic_blocks().len() <= 3 {
+            threshold += threshold / 4;
+        }
+
+        // FIXME: Give a bonus to functions with only a single caller
+
+        let id = tcx.hir.as_local_node_id(callsite.caller).expect("Caller not local");
+        let param_env = ty::ParameterEnvironment::for_item(tcx, id);
+
+        let mut first_block = true;
+        let mut cost = 0;
+
+        // Traverse the MIR manually so we can account for the effects of
+        // inlining on the CFG.
+        let mut work_list = vec![START_BLOCK];
+        let mut visited = BitVector::new(callee_mir.basic_blocks().len());
+        while let Some(bb) = work_list.pop() {
+            if !visited.insert(bb.index()) { continue; }
+            let blk = &callee_mir.basic_blocks()[bb];
+
+            for stmt in &blk.statements {
+                // Don't count StorageLive/StorageDead in the inlining cost.
+                match stmt.kind {
+                    StatementKind::StorageLive(_) |
+                    StatementKind::StorageDead(_) |
+                    StatementKind::Nop => {}
+                    _ => cost += INSTR_COST
+                }
+            }
+            let term = blk.terminator();
+            let mut is_drop = false;
+            match term.kind {
+                TerminatorKind::Drop { ref location, target, unwind } |
+                TerminatorKind::DropAndReplace { ref location, target, unwind, .. } => {
+                    is_drop = true;
+                    work_list.push(target);
+                    // If the location doesn't actually need dropping, treat it like
+                    // a regular goto.
+                    let ty = location.ty(&callee_mir, tcx).subst(tcx, callsite.substs);
+                    let ty = ty.to_ty(tcx);
+                    if tcx.type_needs_drop_given_env(ty, &param_env) {
+                        cost += CALL_PENALTY;
+                        if let Some(unwind) = unwind {
+                            work_list.push(unwind);
+                        }
+                    } else {
+                        cost += INSTR_COST;
+                    }
+                }
+
+                TerminatorKind::Unreachable |
+                TerminatorKind::Call { destination: None, .. } if first_block => {
+                    // If the function always diverges, don't inline
+                    // unless the cost is zero
+                    threshold = 0;
+                }
+
+                TerminatorKind::Call {func: Operand::Constant(ref f), .. } => {
+                    if let ty::TyFnDef(.., f) = f.ty.sty {
+                        // Don't give intrinsics the extra penalty for calls
+                        if f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic {
+                            cost += INSTR_COST;
+                        } else {
+                            cost += CALL_PENALTY;
+                        }
+                    }
+                }
+                TerminatorKind::Assert { .. } => cost += CALL_PENALTY,
+                _ => cost += INSTR_COST
+            }
+
+            if !is_drop {
+                for &succ in &term.successors()[..] {
+                    work_list.push(succ);
+                }
+            }
+
+            first_block = false;
+        }
+
+        // Count up the cost of local variables and temps, if we know the size
+        // use that, otherwise we use a moderately-large dummy cost.
+
+        let ptr_size = tcx.data_layout.pointer_size.bytes();
+
+        for v in callee_mir.vars_and_temps_iter() {
+            let v = &callee_mir.local_decls[v];
+            let ty = v.ty.subst(tcx, callsite.substs);
+            // Cost of the var is the size in machine-words, if we know
+            // it.
+            if let Some(size) = type_size_of(tcx, param_env.clone(), ty) {
+                cost += (size / ptr_size) as usize;
+            } else {
+                cost += UNKNOWN_SIZE_COST;
+            }
+        }
+
+        debug!("Inline cost for {:?} is {}", callsite.callee, cost);
+
+        if let attr::InlineAttr::Always = hint {
+            true
+        } else {
+            cost <= threshold
+        }
+    }
+
+
+    fn inline_call(&self, callsite: CallSite<'tcx>,
+                             caller_mir: &mut Mir<'tcx>, mut callee_mir: Mir<'tcx>) -> bool {
+
+        // Don't inline a function into itself
+        if callsite.caller == callsite.callee { return false; }
+
+        let _task = self.tcx.dep_graph.in_task(DepNode::Mir(callsite.caller));
+
+
+        let terminator = caller_mir[callsite.bb].terminator.take().unwrap();
+        match terminator.kind {
+            // FIXME: Handle inlining of diverging calls
+            TerminatorKind::Call { args, destination: Some(destination), cleanup, .. } => {
+
+                debug!("Inlined {:?} into {:?}", callsite.callee, callsite.caller);
+
+                let is_box_free = Some(callsite.callee) == self.tcx.lang_items.box_free_fn();
+
+                let mut local_map = IndexVec::with_capacity(callee_mir.local_decls.len());
+                let mut scope_map = IndexVec::with_capacity(callee_mir.visibility_scopes.len());
+                let mut promoted_map = IndexVec::with_capacity(callee_mir.promoted.len());
+
+                for mut scope in callee_mir.visibility_scopes.iter().cloned() {
+                    if scope.parent_scope.is_none() {
+                        scope.parent_scope = Some(callsite.location.scope);
+                        scope.span = callee_mir.span;
+                    }
+
+                    scope.span = callsite.location.span;
+
+                    let idx = caller_mir.visibility_scopes.push(scope);
+                    scope_map.push(idx);
+                }
+
+                for loc in callee_mir.vars_and_temps_iter() {
+                    let mut local = callee_mir.local_decls[loc].clone();
+
+                    if let Some(ref mut source_info) = local.source_info {
+                        source_info.scope = scope_map[source_info.scope];
+
+                        source_info.span = callsite.location.span;
+                    }
+
+                    let idx = caller_mir.local_decls.push(local);
+                    local_map.push(idx);
+                }
+
+                for p in callee_mir.promoted.iter().cloned() {
+                    let idx = caller_mir.promoted.push(p);
+                    promoted_map.push(idx);
+                }
+
+                // If the call is something like `a[*i] = f(i)`, where
+                // `i : &mut usize`, then just duplicating the `a[*i]`
+                // Lvalue could result in two different locations if `f`
+                // writes to `i`. To prevent this we need to create a temporary
+                // borrow of the lvalue and pass the destination as `*temp` instead.
+                fn dest_needs_borrow(lval: &Lvalue) -> bool {
+                    match *lval {
+                        Lvalue::Projection(ref p) => {
+                            match p.elem {
+                                ProjectionElem::Deref |
+                                ProjectionElem::Index(_) => true,
+                                _ => dest_needs_borrow(&p.base)
+                            }
+                        }
+                        // Static variables need a borrow because the callee
+                        // might modify the same static.
+                        Lvalue::Static(_) => true,
+                        _ => false
+                    }
+                }
+
+                let dest = if dest_needs_borrow(&destination.0) {
+                    debug!("Creating temp for return destination");
+                    let dest = Rvalue::Ref(
+                        self.tcx.mk_region(ty::ReErased),
+                        BorrowKind::Mut,
+                        destination.0);
+
+                    let ty = dest.ty(caller_mir, self.tcx);
+
+                    let temp = LocalDecl::new_temp(ty);
+
+                    let tmp = caller_mir.local_decls.push(temp);
+                    let tmp = Lvalue::Local(tmp);
+
+                    let stmt = Statement {
+                        source_info: callsite.location,
+                        kind: StatementKind::Assign(tmp.clone(), dest)
+                    };
+                    caller_mir[callsite.bb]
+                        .statements.push(stmt);
+                    tmp.deref()
+                } else {
+                    destination.0
+                };
+
+                let return_block = destination.1;
+
+                let args : Vec<_> = if is_box_free {
+                    assert!(args.len() == 1);
+                    // box_free takes a Box, but is defined with a *mut T, inlining
+                    // needs to generate the cast.
+                    // FIXME: we should probably just generate correct MIR in the first place...
+
+                    let arg = if let Operand::Consume(ref lval) = args[0] {
+                        lval.clone()
+                    } else {
+                        bug!("Constant arg to \"box_free\"");
+                    };
+
+                    let ptr_ty = args[0].ty(caller_mir, self.tcx);
+                    vec![self.cast_box_free_arg(arg, ptr_ty, &callsite, caller_mir)]
+                } else {
+                    // Copy the arguments if needed.
+                    self.make_call_args(args, &callsite, caller_mir)
+                };
+
+                let bb_len = caller_mir.basic_blocks().len();
+                let mut integrator = Integrator {
+                    block_idx: bb_len,
+                    args: &args,
+                    local_map: local_map,
+                    scope_map: scope_map,
+                    promoted_map: promoted_map,
+                    _callsite: callsite,
+                    destination: dest,
+                    return_block: return_block,
+                    cleanup_block: cleanup,
+                    in_cleanup_block: false
+                };
+
+
+                for (bb, mut block) in callee_mir.basic_blocks_mut().drain_enumerated(..) {
+                    integrator.visit_basic_block_data(bb, &mut block);
+                    caller_mir.basic_blocks_mut().push(block);
+                }
+
+                let terminator = Terminator {
+                    source_info: callsite.location,
+                    kind: TerminatorKind::Goto { target: BasicBlock::new(bb_len) }
+                };
+
+                caller_mir[callsite.bb].terminator = Some(terminator);
+
+                true
+            }
+            kind => {
+                caller_mir[callsite.bb].terminator = Some(Terminator {
+                    source_info: terminator.source_info,
+                    kind: kind
+                });
+                false
+            }
+        }
+    }
+
+    fn cast_box_free_arg(&self, arg: Lvalue<'tcx>, ptr_ty: Ty<'tcx>,
+                         callsite: &CallSite<'tcx>, caller_mir: &mut Mir<'tcx>) -> Operand<'tcx> {
+        let arg = Rvalue::Ref(
+            self.tcx.mk_region(ty::ReErased),
+            BorrowKind::Mut,
+            arg.deref());
+
+        let ty = arg.ty(caller_mir, self.tcx);
+        let ref_tmp = LocalDecl::new_temp(ty);
+        let ref_tmp = caller_mir.local_decls.push(ref_tmp);
+        let ref_tmp = Lvalue::Local(ref_tmp);
+
+        let ref_stmt = Statement {
+            source_info: callsite.location,
+            kind: StatementKind::Assign(ref_tmp.clone(), arg)
+        };
+
+        caller_mir[callsite.bb]
+            .statements.push(ref_stmt);
+
+        let pointee_ty = match ptr_ty.sty {
+            ty::TyRawPtr(tm) | ty::TyRef(_, tm) => tm.ty,
+            _ if ptr_ty.is_box() => ptr_ty.boxed_ty(),
+            _ => bug!("Invalid type `{:?}` for call to box_free", ptr_ty)
+        };
+        let ptr_ty = self.tcx.mk_mut_ptr(pointee_ty);
+
+        let raw_ptr = Rvalue::Cast(CastKind::Misc, Operand::Consume(ref_tmp), ptr_ty);
+
+        let cast_tmp = LocalDecl::new_temp(ptr_ty);
+        let cast_tmp = caller_mir.local_decls.push(cast_tmp);
+        let cast_tmp = Lvalue::Local(cast_tmp);
+
+        let cast_stmt = Statement {
+            source_info: callsite.location,
+            kind: StatementKind::Assign(cast_tmp.clone(), raw_ptr)
+        };
+
+        caller_mir[callsite.bb]
+            .statements.push(cast_stmt);
+
+        Operand::Consume(cast_tmp)
+    }
+
+    fn make_call_args(&self, args: Vec<Operand<'tcx>>,
+                      callsite: &CallSite<'tcx>, caller_mir: &mut Mir<'tcx>) -> Vec<Operand<'tcx>> {
+        let tcx = self.tcx;
+        // FIXME: Analysis of the usage of the arguments to avoid
+        // unnecessary temporaries.
+        args.into_iter().map(|a| {
+            if let Operand::Consume(Lvalue::Local(local)) = a {
+                if caller_mir.local_kind(local) == LocalKind::Temp {
+                    // Reuse the operand if it's a temporary already
+                    return a;
+                }
+            }
+
+            debug!("Creating temp for argument");
+            // Otherwise, create a temporary for the arg
+            let arg = Rvalue::Use(a);
+
+            let ty = arg.ty(caller_mir, tcx);
+
+            let arg_tmp = LocalDecl::new_temp(ty);
+            let arg_tmp = caller_mir.local_decls.push(arg_tmp);
+            let arg_tmp = Lvalue::Local(arg_tmp);
+
+            let stmt = Statement {
+                source_info: callsite.location,
+                kind: StatementKind::Assign(arg_tmp.clone(), arg)
+            };
+            caller_mir[callsite.bb].statements.push(stmt);
+            Operand::Consume(arg_tmp)
+        }).collect()
+    }
+}
+
+fn type_size_of<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, param_env: ty::ParameterEnvironment<'tcx>,
+                          ty: Ty<'tcx>) -> Option<u64> {
+    tcx.infer_ctxt(param_env, traits::Reveal::All).enter(|infcx| {
+        ty.layout(&infcx).ok().map(|layout| {
+            layout.size(&tcx.data_layout).bytes()
+        })
+    })
+}
+
+/**
+ * Integrator.
+ *
+ * Integrates blocks from the callee function into the calling function.
+ * Updates block indices, references to locals and other control flow
+ * stuff.
+ */
+struct Integrator<'a, 'tcx: 'a> {
+    block_idx: usize,
+    args: &'a [Operand<'tcx>],
+    local_map: IndexVec<Local, Local>,
+    scope_map: IndexVec<VisibilityScope, VisibilityScope>,
+    promoted_map: IndexVec<Promoted, Promoted>,
+    _callsite: CallSite<'tcx>,
+    destination: Lvalue<'tcx>,
+    return_block: BasicBlock,
+    cleanup_block: Option<BasicBlock>,
+    in_cleanup_block: bool,
+}
+
+impl<'a, 'tcx> Integrator<'a, 'tcx> {
+    fn update_target(&self, tgt: BasicBlock) -> BasicBlock {
+        let new = BasicBlock::new(tgt.index() + self.block_idx);
+        debug!("Updating target `{:?}`, new: `{:?}`", tgt, new);
+        new
+    }
+
+    fn update_local(&self, local: Local) -> Option<Local> {
+        let idx = local.index();
+        if idx < (self.args.len() + 1) {
+            return None;
+        }
+        let idx = idx - (self.args.len() + 1);
+        let local = Local::new(idx);
+        self.local_map.get(local).cloned()
+    }
+
+    fn arg_index(&self, arg: Local) -> Option<usize> {
+        let idx = arg.index();
+        if idx > 0 && idx <= self.args.len() {
+            Some(idx - 1)
+        } else {
+            None
+        }
+    }
+}
+
+impl<'a, 'tcx> MutVisitor<'tcx> for Integrator<'a, 'tcx> {
+    fn visit_lvalue(&mut self,
+                    lvalue: &mut Lvalue<'tcx>,
+                    _ctxt: LvalueContext<'tcx>,
+                    _location: Location) {
+        if let Lvalue::Local(ref mut local) = *lvalue {
+            if let Some(l) = self.update_local(*local) {
+                // Temp or Var; update the local reference
+                *local = l;
+                return;
+            }
+        }
+        if let Lvalue::Local(local) = *lvalue {
+            if local == RETURN_POINTER {
+                // Return pointer; update the lvalue itself
+                *lvalue = self.destination.clone();
+            } else if local.index() < (self.args.len() + 1) {
+                // Argument, once again update the the lvalue itself
+                let idx = local.index() - 1;
+                if let Operand::Consume(ref lval) = self.args[idx] {
+                    *lvalue = lval.clone();
+                } else {
+                    bug!("Arg operand `{:?}` is not an Lvalue use.", idx)
+                }
+            }
+        } else {
+            self.super_lvalue(lvalue, _ctxt, _location)
+        }
+    }
+
+    fn visit_operand(&mut self, operand: &mut Operand<'tcx>, location: Location) {
+        if let Operand::Consume(Lvalue::Local(arg)) = *operand {
+            if let Some(idx) = self.arg_index(arg) {
+                let new_arg = self.args[idx].clone();
+                *operand = new_arg;
+                return;
+            }
+        }
+        self.super_operand(operand, location);
+    }
+
+    fn visit_basic_block_data(&mut self, block: BasicBlock, data: &mut BasicBlockData<'tcx>) {
+        self.in_cleanup_block = data.is_cleanup;
+        self.super_basic_block_data(block, data);
+        self.in_cleanup_block = false;
+    }
+
+    fn visit_terminator_kind(&mut self, block: BasicBlock,
+                             kind: &mut TerminatorKind<'tcx>, loc: Location) {
+        self.super_terminator_kind(block, kind, loc);
+
+        match *kind {
+            TerminatorKind::Goto { ref mut target} => {
+                *target = self.update_target(*target);
+            }
+            TerminatorKind::SwitchInt { ref mut targets, .. } => {
+                for tgt in targets {
+                    *tgt = self.update_target(*tgt);
+                }
+            }
+            TerminatorKind::Drop { ref mut target, ref mut unwind, .. } |
+            TerminatorKind::DropAndReplace { ref mut target, ref mut unwind, .. } => {
+                *target = self.update_target(*target);
+                if let Some(tgt) = *unwind {
+                    *unwind = Some(self.update_target(tgt));
+                } else if !self.in_cleanup_block {
+                    // Unless this drop is in a cleanup block, add an unwind edge to
+                    // the orignal call's cleanup block
+                    *unwind = self.cleanup_block;
+                }
+            }
+            TerminatorKind::Call { ref mut destination, ref mut cleanup, .. } => {
+                if let Some((_, ref mut tgt)) = *destination {
+                    *tgt = self.update_target(*tgt);
+                }
+                if let Some(tgt) = *cleanup {
+                    *cleanup = Some(self.update_target(tgt));
+                } else if !self.in_cleanup_block {
+                    // Unless this call is in a cleanup block, add an unwind edge to
+                    // the orignal call's cleanup block
+                    *cleanup = self.cleanup_block;
+                }
+            }
+            TerminatorKind::Assert { ref mut target, ref mut cleanup, .. } => {
+                *target = self.update_target(*target);
+                if let Some(tgt) = *cleanup {
+                    *cleanup = Some(self.update_target(tgt));
+                } else if !self.in_cleanup_block {
+                    // Unless this assert is in a cleanup block, add an unwind edge to
+                    // the orignal call's cleanup block
+                    *cleanup = self.cleanup_block;
+                }
+            }
+            TerminatorKind::Return => {
+                *kind = TerminatorKind::Goto { target: self.return_block };
+            }
+            TerminatorKind::Resume => {
+                if let Some(tgt) = self.cleanup_block {
+                    *kind = TerminatorKind::Goto { target: tgt }
+                }
+            }
+            TerminatorKind::Unreachable => { }
+        }
+    }
+
+    fn visit_visibility_scope(&mut self, scope: &mut VisibilityScope) {
+        *scope = self.scope_map[*scope];
+    }
+
+    fn visit_literal(&mut self, literal: &mut Literal<'tcx>, loc: Location) {
+        if let Literal::Promoted { ref mut index } = *literal {
+            if let Some(p) = self.promoted_map.get(*index).cloned() {
+                *index = p;
+            }
+        } else {
+            self.super_literal(literal, loc);
+        }
+    }
+}

src/librustc_mir/transform/mod.rs

@@ -20,3 +20,4 @@ pub mod dump_mir;
 pub mod deaggregator;
 pub mod instcombine;
 pub mod copy_prop;
+pub mod inline;

src/librustc_mir/transform/simplify.rs

@@ -79,7 +79,7 @@ pub struct CfgSimplifier<'a, 'tcx: 'a> {
 }
 
 impl<'a, 'tcx: 'a> CfgSimplifier<'a, 'tcx> {
-    fn new(mir: &'a mut Mir<'tcx>) -> Self {
+    pub fn new(mir: &'a mut Mir<'tcx>) -> Self {
         let mut pred_count = IndexVec::from_elem(0u32, mir.basic_blocks());
 
         // we can't use mir.predecessors() here because that counts
@@ -102,7 +102,7 @@ impl<'a, 'tcx: 'a> CfgSimplifier<'a, 'tcx> {
         }
     }
 
-    fn simplify(mut self) {
+    pub fn simplify(mut self) {
         loop {
             let mut changed = false;
 
@@ -137,6 +137,8 @@ impl<'a, 'tcx: 'a> CfgSimplifier<'a, 'tcx> {
 
             if !changed { break }
         }
+
+        self.strip_nops()
     }
 
     // Collapse a goto chain starting from `start`
@@ -231,9 +233,19 @@ impl<'a, 'tcx: 'a> CfgSimplifier<'a, 'tcx> {
         terminator.kind = TerminatorKind::Goto { target: first_succ };
         true
     }
+
+    fn strip_nops(&mut self) {
+        for blk in self.basic_blocks.iter_mut() {
+            blk.statements.retain(|stmt| if let StatementKind::Nop = stmt.kind {
+                false
+            } else {
+                true
+            })
+        }
+    }
 }
 
-fn remove_dead_blocks(mir: &mut Mir) {
+pub fn remove_dead_blocks(mir: &mut Mir) {
     let mut seen = BitVector::new(mir.basic_blocks().len());
     for (bb, _) in traversal::preorder(mir) {
         seen.insert(bb.index());