1 // Copyright 2016 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! Performs various peephole optimizations.
13 use rustc::mir::repr::{Location, Lvalue, Mir, Operand, ProjectionElem, Rvalue};
14 use rustc::mir::transform::{MirPass, MirSource, Pass};
15 use rustc::mir::visit::{MutVisitor, Visitor};
16 use rustc::ty::TyCtxt;
17 use rustc::util::nodemap::FnvHashSet;
20 pub struct InstCombine {
21 optimizations: OptimizationList,
25 pub fn new() -> InstCombine {
27 optimizations: OptimizationList::default(),
32 impl Pass for InstCombine {}
34 impl<'tcx> MirPass<'tcx> for InstCombine {
35 fn run_pass<'a>(&mut self,
36 tcx: TyCtxt<'a, 'tcx, 'tcx>,
38 mir: &mut Mir<'tcx>) {
39 // We only run when optimizing MIR (at any level).
40 if tcx.sess.opts.debugging_opts.mir_opt_level == Some(0) {
44 // First, find optimization opportunities. This is done in a pre-pass to keep the MIR
45 // read-only so that we can do global analyses on the MIR in the process (e.g.
48 let mut optimization_finder = OptimizationFinder::new(mir, tcx);
49 optimization_finder.visit_mir(mir);
50 self.optimizations = optimization_finder.optimizations
53 // Then carry out those optimizations.
54 MutVisitor::visit_mir(&mut *self, mir);
58 impl<'tcx> MutVisitor<'tcx> for InstCombine {
59 fn visit_rvalue(&mut self, rvalue: &mut Rvalue<'tcx>, location: Location) {
60 if self.optimizations.and_stars.remove(&location) {
61 debug!("Replacing `&*`: {:?}", rvalue);
62 let new_lvalue = match *rvalue {
63 Rvalue::Ref(_, _, Lvalue::Projection(ref mut projection)) => {
64 mem::replace(&mut projection.base, Lvalue::ReturnPointer)
66 _ => bug!("Detected `&*` but didn't find `&*`!"),
68 *rvalue = Rvalue::Use(Operand::Consume(new_lvalue))
71 self.super_rvalue(rvalue, location)
75 /// Finds optimization opportunities on the MIR.
76 struct OptimizationFinder<'b, 'a, 'tcx:'a+'b> {
78 tcx: TyCtxt<'a, 'tcx, 'tcx>,
79 optimizations: OptimizationList,
82 impl<'b, 'a, 'tcx:'b> OptimizationFinder<'b, 'a, 'tcx> {
83 fn new(mir: &'b Mir<'tcx>, tcx: TyCtxt<'a, 'tcx, 'tcx>) -> OptimizationFinder<'b, 'a, 'tcx> {
87 optimizations: OptimizationList::default(),
92 impl<'b, 'a, 'tcx> Visitor<'tcx> for OptimizationFinder<'b, 'a, 'tcx> {
93 fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
94 if let Rvalue::Ref(_, _, Lvalue::Projection(ref projection)) = *rvalue {
95 if let ProjectionElem::Deref = projection.elem {
96 if projection.base.ty(self.mir, self.tcx).to_ty(self.tcx).is_region_ptr() {
97 self.optimizations.and_stars.insert(location);
102 self.super_rvalue(rvalue, location)
107 struct OptimizationList {
108 and_stars: FnvHashSet<Location>,