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librustc_mir: Remove
&*x
when x
has a reference type.
This introduces a new `InstCombine` pass for us to place such peephole optimizations.
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@@ -0,0 +1,110 @@ | ||
// 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. | ||
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//! Performs various peephole optimizations. | ||
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use rustc::mir::repr::{Location, Lvalue, Mir, Operand, ProjectionElem, Rvalue}; | ||
use rustc::mir::transform::{MirPass, MirSource, Pass}; | ||
use rustc::mir::visit::{MutVisitor, Visitor}; | ||
use rustc::ty::TyCtxt; | ||
use rustc::util::nodemap::FnvHashSet; | ||
use std::mem; | ||
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pub struct InstCombine { | ||
optimizations: OptimizationList, | ||
} | ||
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impl InstCombine { | ||
pub fn new() -> InstCombine { | ||
InstCombine { | ||
optimizations: OptimizationList::default(), | ||
} | ||
} | ||
} | ||
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impl Pass for InstCombine {} | ||
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impl<'tcx> MirPass<'tcx> for InstCombine { | ||
fn run_pass<'a>(&mut 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 == Some(0) { | ||
return | ||
} | ||
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// 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 mut optimization_finder = OptimizationFinder::new(mir, tcx); | ||
optimization_finder.visit_mir(mir); | ||
self.optimizations = optimization_finder.optimizations | ||
} | ||
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// Then carry out those optimizations. | ||
MutVisitor::visit_mir(&mut *self, mir); | ||
} | ||
} | ||
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impl<'tcx> MutVisitor<'tcx> for InstCombine { | ||
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)) => { | ||
mem::replace(&mut projection.base, Lvalue::ReturnPointer) | ||
} | ||
_ => bug!("Detected `&*` but didn't find `&*`!"), | ||
}; | ||
*rvalue = Rvalue::Use(Operand::Consume(new_lvalue)) | ||
} | ||
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self.super_rvalue(rvalue, location) | ||
} | ||
} | ||
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/// Finds optimization opportunities on the MIR. | ||
struct OptimizationFinder<'b, 'a, 'tcx:'a+'b> { | ||
mir: &'b Mir<'tcx>, | ||
tcx: TyCtxt<'a, 'tcx, 'tcx>, | ||
optimizations: OptimizationList, | ||
} | ||
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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: mir, | ||
tcx: tcx, | ||
optimizations: OptimizationList::default(), | ||
} | ||
} | ||
} | ||
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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); | ||
} | ||
} | ||
} | ||
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self.super_rvalue(rvalue, location) | ||
} | ||
} | ||
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#[derive(Default)] | ||
struct OptimizationList { | ||
and_stars: FnvHashSet<Location>, | ||
} | ||
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Original file line number | Diff line number | Diff line change |
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@@ -18,3 +18,5 @@ pub mod promote_consts; | |
pub mod qualify_consts; | ||
pub mod dump_mir; | ||
pub mod deaggregator; | ||
pub mod instcombine; | ||
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