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// 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.
//! Performs various peephole optimizations.
use rustc::mir::{Location, Lvalue, Mir, Operand, ProjectionElem, Rvalue, Local};
use rustc::mir::transform::{MirPass, MirSource};
use rustc::mir::visit::{MutVisitor, Visitor};
use rustc::ty::TyCtxt;
use rustc::util::nodemap::FxHashSet;
use rustc_data_structures::indexed_vec::Idx;
use std::mem;
pub struct InstCombine;
impl MirPass for InstCombine {
fn run_pass<'a, 'tcx>(&self,
tcx: TyCtxt<'a, 'tcx, 'tcx>,
_: MirSource,
mir: &mut Mir<'tcx>) {
// We only run when optimizing MIR (at any level).
if tcx.sess.opts.debugging_opts.mir_opt_level == 0 {
return
}
// First, find optimization opportunities. This is done in a pre-pass to keep the MIR
// read-only so that we can do global analyses on the MIR in the process (e.g.
// `Lvalue::ty()`).
let optimizations = {
let mut optimization_finder = OptimizationFinder::new(mir, tcx);
optimization_finder.visit_mir(mir);
optimization_finder.optimizations
};
// Then carry out those optimizations.
MutVisitor::visit_mir(&mut InstCombineVisitor { optimizations }, mir);
}
}
pub struct InstCombineVisitor {
optimizations: OptimizationList,
}
impl<'tcx> MutVisitor<'tcx> for InstCombineVisitor {
fn visit_rvalue(&mut self, rvalue: &mut Rvalue<'tcx>, location: Location) {
if self.optimizations.and_stars.remove(&location) {
debug!("Replacing `&*`: {:?}", rvalue);
let new_lvalue = match *rvalue {
Rvalue::Ref(_, _, Lvalue::Projection(ref mut projection)) => {
// Replace with dummy
mem::replace(&mut projection.base, Lvalue::Local(Local::new(0)))
}
_ => bug!("Detected `&*` but didn't find `&*`!"),
};
*rvalue = Rvalue::Use(Operand::Consume(new_lvalue))
}
self.super_rvalue(rvalue, location)
}
}
/// Finds optimization opportunities on the MIR.
struct OptimizationFinder<'b, 'a, 'tcx:'a+'b> {
mir: &'b Mir<'tcx>,
tcx: TyCtxt<'a, 'tcx, 'tcx>,
optimizations: OptimizationList,
}
impl<'b, 'a, 'tcx:'b> OptimizationFinder<'b, 'a, 'tcx> {
fn new(mir: &'b Mir<'tcx>, tcx: TyCtxt<'a, 'tcx, 'tcx>) -> OptimizationFinder<'b, 'a, 'tcx> {
OptimizationFinder {
mir,
tcx,
optimizations: OptimizationList::default(),
}
}
}
impl<'b, 'a, 'tcx> Visitor<'tcx> for OptimizationFinder<'b, 'a, 'tcx> {
fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
if let Rvalue::Ref(_, _, Lvalue::Projection(ref projection)) = *rvalue {
if let ProjectionElem::Deref = projection.elem {
if projection.base.ty(self.mir, self.tcx).to_ty(self.tcx).is_region_ptr() {
self.optimizations.and_stars.insert(location);
}
}
}
self.super_rvalue(rvalue, location)
}
}
#[derive(Default)]
struct OptimizationList {
and_stars: FxHashSet<Location>,
}
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