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move to separate pass, cache layouts

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This commit is contained in:
Erik Desjardins 2021-03-16 21:30:37 -04:00
parent 90562b401e
commit bca761dc5d
3 changed files with 52 additions and 26 deletions
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27
compiler/rustc_mir/src/transform/instcombine.rs
View File

@ -12,12 +12,10 @@ pub struct InstCombine;
impl<'tcx> MirPass<'tcx> for InstCombine {
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
let param_env = tcx.param_env(body.source.def_id());
let (basic_blocks, local_decls) = body.basic_blocks_and_local_decls_mut();
let ctx = InstCombineContext { tcx, local_decls, param_env };
let ctx = InstCombineContext { tcx, local_decls };
for block in basic_blocks.iter_mut() {
for statement in block.statements.iter_mut() {
ctx.combine_zst(&statement.source_info, &mut statement.kind);
match statement.kind {
StatementKind::Assign(box (_place, ref mut rvalue)) => {
ctx.combine_bool_cmp(&statement.source_info, rvalue);
@ -34,7 +32,6 @@ impl<'tcx> MirPass<'tcx> for InstCombine {
struct InstCombineContext<'tcx, 'a> {
tcx: TyCtxt<'tcx>,
local_decls: &'a LocalDecls<'tcx>,
param_env: ty::ParamEnv<'tcx>,
}
impl<'tcx, 'a> InstCombineContext<'tcx, 'a> {
@ -44,28 +41,6 @@ impl<'tcx, 'a> InstCombineContext<'tcx, 'a> {
})
}
/// Remove assignments to inhabited ZST places.
fn combine_zst(&self, source_info: &SourceInfo, kind: &mut StatementKind<'tcx>) {
match kind {
StatementKind::Assign(box (place, _)) => {
let place_ty = place.ty(self.local_decls, self.tcx).ty;
if let Ok(layout) = self.tcx.layout_of(self.param_env.and(place_ty)) {
if layout.is_zst() && !layout.abi.is_uninhabited() {
if self.tcx.consider_optimizing(|| {
format!(
"InstCombine ZST - Place: {:?} SourceInfo: {:?}",
place, source_info
)
}) {
*kind = StatementKind::Nop;
}
}
}
}
_ => {}
}
}
/// Transform boolean comparisons into logical operations.
fn combine_bool_cmp(&self, source_info: &SourceInfo, rvalue: &mut Rvalue<'tcx>) {
match rvalue {

2
compiler/rustc_mir/src/transform/mod.rs
View File

@ -44,6 +44,7 @@ pub mod promote_consts;
pub mod remove_noop_landing_pads;
pub mod remove_storage_markers;
pub mod remove_unneeded_drops;
pub mod remove_zsts;
pub mod required_consts;
pub mod rustc_peek;
pub mod simplify;
@ -494,6 +495,7 @@ fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
// The main optimizations that we do on MIR.
let optimizations: &[&dyn MirPass<'tcx>] = &[
&remove_storage_markers::RemoveStorageMarkers,
&remove_zsts::RemoveZsts,
&const_goto::ConstGoto,
&remove_unneeded_drops::RemoveUnneededDrops,
&match_branches::MatchBranchSimplification,

49
compiler/rustc_mir/src/transform/remove_zsts.rs Normal file
View File

@ -0,0 +1,49 @@
//! Removes assignments to ZST places.
use crate::transform::MirPass;
use rustc_data_structures::fx::FxHashMap;
use rustc_middle::mir::{Body, StatementKind};
use rustc_middle::ty::TyCtxt;
pub struct RemoveZsts;
impl<'tcx> MirPass<'tcx> for RemoveZsts {
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
let param_env = tcx.param_env(body.source.def_id());
let (basic_blocks, local_decls) = body.basic_blocks_and_local_decls_mut();
let mut is_zst_cache = FxHashMap::default();
for block in basic_blocks.iter_mut() {
for statement in block.statements.iter_mut() {
match statement.kind {
StatementKind::Assign(box (place, _)) => {
let place_ty = place.ty(local_decls, tcx).ty;
let is_inhabited_zst = *is_zst_cache.entry(place_ty).or_insert_with(|| {
if let Ok(layout) = tcx.layout_of(param_env.and(place_ty)) {
if layout.is_zst() && !layout.abi.is_uninhabited() {
return true;
}
}
false
});
if is_inhabited_zst {
if tcx.consider_optimizing(|| {
format!(
"RemoveZsts - Place: {:?} SourceInfo: {:?}",
place, statement.source_info
)
}) {
statement.make_nop();
}
}
}
_ => {}
}
}
}
}
}