115 lines
4.0 KiB
Rust
115 lines
4.0 KiB
Rust
//! Performs various peephole optimizations.
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use rustc::mir::{Constant, Location, Place, PlaceBase, Body, Operand, ProjectionElem, Rvalue,
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Local};
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use rustc::mir::visit::{MutVisitor, Visitor};
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use rustc::ty::{self, TyCtxt};
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use rustc::util::nodemap::{FxHashMap, FxHashSet};
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use rustc_data_structures::indexed_vec::Idx;
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use std::mem;
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use crate::transform::{MirPass, MirSource};
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pub struct InstCombine;
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impl MirPass for InstCombine {
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fn run_pass<'tcx>(&self, tcx: TyCtxt<'tcx>, _: MirSource<'tcx>, body: &mut Body<'tcx>) {
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// We only run when optimizing MIR (at any level).
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if tcx.sess.opts.debugging_opts.mir_opt_level == 0 {
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return
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}
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// First, find optimization opportunities. This is done in a pre-pass to keep the MIR
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// read-only so that we can do global analyses on the MIR in the process (e.g.
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// `Place::ty()`).
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let optimizations = {
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let mut optimization_finder = OptimizationFinder::new(body, tcx);
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optimization_finder.visit_body(body);
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optimization_finder.optimizations
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};
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// Then carry out those optimizations.
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MutVisitor::visit_body(&mut InstCombineVisitor { optimizations }, body);
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}
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}
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pub struct InstCombineVisitor<'tcx> {
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optimizations: OptimizationList<'tcx>,
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}
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impl<'tcx> MutVisitor<'tcx> for InstCombineVisitor<'tcx> {
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fn visit_rvalue(&mut self, rvalue: &mut Rvalue<'tcx>, location: Location) {
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if self.optimizations.and_stars.remove(&location) {
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debug!("replacing `&*`: {:?}", rvalue);
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let new_place = match *rvalue {
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Rvalue::Ref(_, _, Place {
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ref mut base,
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projection: Some(ref mut projection),
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}) => Place {
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// Replace with dummy
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base: mem::replace(base, PlaceBase::Local(Local::new(0))),
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projection: projection.base.take(),
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},
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_ => bug!("Detected `&*` but didn't find `&*`!"),
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};
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*rvalue = Rvalue::Use(Operand::Copy(new_place))
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}
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if let Some(constant) = self.optimizations.arrays_lengths.remove(&location) {
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debug!("replacing `Len([_; N])`: {:?}", rvalue);
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*rvalue = Rvalue::Use(Operand::Constant(box constant));
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}
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self.super_rvalue(rvalue, location)
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}
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}
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/// Finds optimization opportunities on the MIR.
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struct OptimizationFinder<'b, 'tcx> {
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body: &'b Body<'tcx>,
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tcx: TyCtxt<'tcx>,
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optimizations: OptimizationList<'tcx>,
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}
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impl OptimizationFinder<'b, 'tcx> {
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fn new(body: &'b Body<'tcx>, tcx: TyCtxt<'tcx>) -> OptimizationFinder<'b, 'tcx> {
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OptimizationFinder {
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body,
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tcx,
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optimizations: OptimizationList::default(),
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}
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}
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}
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impl Visitor<'tcx> for OptimizationFinder<'b, 'tcx> {
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fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
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if let Rvalue::Ref(_, _, Place {
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ref base,
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projection: Some(ref projection),
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}) = *rvalue {
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if let ProjectionElem::Deref = projection.elem {
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if Place::ty_from(&base, &projection.base, self.body, self.tcx).ty.is_region_ptr() {
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self.optimizations.and_stars.insert(location);
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}
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}
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}
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if let Rvalue::Len(ref place) = *rvalue {
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let place_ty = place.ty(&self.body.local_decls, self.tcx).ty;
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if let ty::Array(_, len) = place_ty.sty {
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let span = self.body.source_info(location).span;
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let ty = self.tcx.types.usize;
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let constant = Constant { span, ty, literal: len, user_ty: None };
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self.optimizations.arrays_lengths.insert(location, constant);
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}
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}
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self.super_rvalue(rvalue, location)
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}
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}
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#[derive(Default)]
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struct OptimizationList<'tcx> {
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and_stars: FxHashSet<Location>,
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arrays_lengths: FxHashMap<Location, Constant<'tcx>>,
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}
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