diff --git a/src/librustc_driver/driver.rs b/src/librustc_driver/driver.rs index 36e9fccdf5fd8..14cd05279b1ca 100644 --- a/src/librustc_driver/driver.rs +++ b/src/librustc_driver/driver.rs @@ -1017,6 +1017,7 @@ pub fn phase_4_translate_to_llvm<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, passes.push_pass(box mir::transform::no_landing_pads::NoLandingPads); passes.push_pass(box mir::transform::simplify_cfg::SimplifyCfg::new("no-landing-pads")); + // From here on out, regions are gone. passes.push_pass(box mir::transform::erase_regions::EraseRegions); passes.push_pass(box mir::transform::add_call_guards::AddCallGuards); @@ -1024,6 +1025,8 @@ pub fn phase_4_translate_to_llvm<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, passes.push_pass(box mir::transform::no_landing_pads::NoLandingPads); passes.push_pass(box mir::transform::simplify_cfg::SimplifyCfg::new("elaborate-drops")); + // No lifetime analysis based on borrowing can be done from here on out. + passes.push_pass(box mir::transform::instcombine::InstCombine::new()); passes.push_pass(box mir::transform::deaggregator::Deaggregator); passes.push_pass(box mir::transform::add_call_guards::AddCallGuards); diff --git a/src/librustc_mir/transform/instcombine.rs b/src/librustc_mir/transform/instcombine.rs new file mode 100644 index 0000000000000..a0331f03b0197 --- /dev/null +++ b/src/librustc_mir/transform/instcombine.rs @@ -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 or the MIT license +// , at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +//! Performs various peephole optimizations. + +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; + +pub struct InstCombine { + optimizations: OptimizationList, +} + +impl InstCombine { + pub fn new() -> InstCombine { + InstCombine { + optimizations: OptimizationList::default(), + } + } +} + +impl Pass for InstCombine {} + +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 + } + + // 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 + } + + // Then carry out those optimizations. + MutVisitor::visit_mir(&mut *self, mir); + } +} + +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)) + } + + 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: mir, + tcx: 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: FnvHashSet, +} + diff --git a/src/librustc_mir/transform/mod.rs b/src/librustc_mir/transform/mod.rs index c3485b8256da1..e99b7a976e3e3 100644 --- a/src/librustc_mir/transform/mod.rs +++ b/src/librustc_mir/transform/mod.rs @@ -18,3 +18,5 @@ pub mod promote_consts; pub mod qualify_consts; pub mod dump_mir; pub mod deaggregator; +pub mod instcombine; +