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::{Constant, Location, Place, Mir, Operand, ProjectionElem, Rvalue, Local};
14 use rustc::mir::visit::{MutVisitor, Visitor};
15 use rustc::ty::{TyCtxt, TypeVariants};
16 use rustc::util::nodemap::{FxHashMap, FxHashSet};
17 use rustc_data_structures::indexed_vec::Idx;
19 use transform::{MirPass, MirSource};
21 pub struct InstCombine;
23 impl MirPass for InstCombine {
24 fn run_pass<'a, 'tcx>(&self,
25 tcx: TyCtxt<'a, 'tcx, 'tcx>,
27 mir: &mut Mir<'tcx>) {
28 // We only run when optimizing MIR (at any level).
29 if tcx.sess.opts.debugging_opts.mir_opt_level == 0 {
33 // First, find optimization opportunities. This is done in a pre-pass to keep the MIR
34 // read-only so that we can do global analyses on the MIR in the process (e.g.
37 let mut optimization_finder = OptimizationFinder::new(mir, tcx);
38 optimization_finder.visit_mir(mir);
39 optimization_finder.optimizations
42 // Then carry out those optimizations.
43 MutVisitor::visit_mir(&mut InstCombineVisitor { optimizations }, mir);
47 pub struct InstCombineVisitor<'tcx> {
48 optimizations: OptimizationList<'tcx>,
51 impl<'tcx> MutVisitor<'tcx> for InstCombineVisitor<'tcx> {
52 fn visit_rvalue(&mut self, rvalue: &mut Rvalue<'tcx>, location: Location) {
53 if self.optimizations.and_stars.remove(&location) {
54 debug!("Replacing `&*`: {:?}", rvalue);
55 let new_place = match *rvalue {
56 Rvalue::Ref(_, _, Place::Projection(ref mut projection)) => {
58 mem::replace(&mut projection.base, Place::Local(Local::new(0)))
60 _ => bug!("Detected `&*` but didn't find `&*`!"),
62 *rvalue = Rvalue::Use(Operand::Copy(new_place))
65 if let Some(constant) = self.optimizations.arrays_lengths.remove(&location) {
66 debug!("Replacing `Len([_; N])`: {:?}", rvalue);
67 *rvalue = Rvalue::Use(Operand::Constant(box constant));
70 self.super_rvalue(rvalue, location)
74 /// Finds optimization opportunities on the MIR.
75 struct OptimizationFinder<'b, 'a, 'tcx:'a+'b> {
77 tcx: TyCtxt<'a, 'tcx, 'tcx>,
78 optimizations: OptimizationList<'tcx>,
81 impl<'b, 'a, 'tcx:'b> OptimizationFinder<'b, 'a, 'tcx> {
82 fn new(mir: &'b Mir<'tcx>, tcx: TyCtxt<'a, 'tcx, 'tcx>) -> OptimizationFinder<'b, 'a, 'tcx> {
86 optimizations: OptimizationList::default(),
91 impl<'b, 'a, 'tcx> Visitor<'tcx> for OptimizationFinder<'b, 'a, 'tcx> {
92 fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
93 if let Rvalue::Ref(_, _, Place::Projection(ref projection)) = *rvalue {
94 if let ProjectionElem::Deref = projection.elem {
95 if projection.base.ty(self.mir, self.tcx).to_ty(self.tcx).is_region_ptr() {
96 self.optimizations.and_stars.insert(location);
101 if let Rvalue::Len(ref place) = *rvalue {
102 let place_ty = place.ty(&self.mir.local_decls, self.tcx).to_ty(self.tcx);
103 if let TypeVariants::TyArray(_, len) = place_ty.sty {
104 let span = self.mir.source_info(location).span;
105 let ty = self.tcx.types.usize;
106 let constant = Constant { span, ty, literal: len };
107 self.optimizations.arrays_lengths.insert(location, constant);
111 self.super_rvalue(rvalue, location)
116 struct OptimizationList<'tcx> {
117 and_stars: FxHashSet<Location>,
118 arrays_lengths: FxHashMap<Location, Constant<'tcx>>,