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‎compiler/rustc_mir/src/transform/dest_prop.rs

Lines changed: 59 additions & 21 deletions
Original file line numberDiff line numberDiff line change
@@ -95,12 +95,13 @@
9595
//! [previous attempt]: https://github.com/rust-lang/rust/pull/47954
9696
//! [subsequent approach]: https://github.com/rust-lang/rust/pull/71003
9797
98-
use crate::dataflow::{self, Analysis};
98+
use crate::dataflow::impls::{MaybeInitializedLocals, MaybeLiveLocals};
99+
use crate::dataflow::Analysis;
99100
use crate::{
100101
transform::{MirPass, MirSource},
101102
util::{dump_mir, PassWhere},
102103
};
103-
use dataflow::impls::{MaybeInitializedLocals, MaybeLiveLocals};
104+
use itertools::Itertools;
104105
use rustc_data_structures::unify::{InPlaceUnificationTable, UnifyKey};
105106
use rustc_index::{
106107
bit_set::{BitMatrix, BitSet},
@@ -255,12 +256,14 @@ impl Replacements<'tcx> {
255256

256257
// We still return `Err` in any case, as `src` and `dest` do not need to be unified
257258
// *again*.
259+
trace!("push({:?}): already unified", candidate);
258260
return Err(());
259261
}
260262

261263
let entry = &mut self.map[candidate.src];
262264
if entry.is_some() {
263265
// We're already replacing `src` with something else, so this candidate is out.
266+
trace!("push({:?}): src already has replacement", candidate);
264267
return Err(());
265268
}
266269

@@ -270,6 +273,7 @@ impl Replacements<'tcx> {
270273
self.kill.insert(candidate.src);
271274
self.kill.insert(candidate.dest.local);
272275

276+
trace!("push({:?}): accepted", candidate);
273277
Ok(())
274278
}
275279

@@ -535,7 +539,7 @@ impl Conflicts<'a> {
535539

536540
trace!("record conflicts at {:?}", loc);
537541

538-
this.record_conflicts(&mut live_and_init_locals[statement_index]);
542+
this.record_dataflow_conflicts(&mut live_and_init_locals[statement_index]);
539543
}
540544

541545
init.seek_to_block_end(block);
@@ -544,13 +548,13 @@ impl Conflicts<'a> {
544548
conflicts.intersect(live.get());
545549
trace!("record conflicts at end of {:?}", block);
546550

547-
this.record_conflicts(&mut conflicts);
551+
this.record_dataflow_conflicts(&mut conflicts);
548552
}
549553

550554
this
551555
}
552556

553-
fn record_conflicts(&mut self, new_conflicts: &mut BitSet<Local>) {
557+
fn record_dataflow_conflicts(&mut self, new_conflicts: &mut BitSet<Local>) {
554558
// Remove all locals that are not candidates.
555559
new_conflicts.intersect(self.relevant_locals);
556560

@@ -559,6 +563,12 @@ impl Conflicts<'a> {
559563
}
560564
}
561565

566+
fn record_local_conflict(&mut self, a: Local, b: Local, why: &str) {
567+
trace!("conflict {:?} <-> {:?} due to {}", a, b, why);
568+
self.matrix.insert(a, b);
569+
self.matrix.insert(b, a);
570+
}
571+
562572
/// Records locals that must not overlap during the evaluation of `stmt`. These locals conflict
563573
/// and must not be merged.
564574
fn record_statement_conflicts(&mut self, stmt: &Statement<'_>) {
@@ -575,8 +585,11 @@ impl Conflicts<'a> {
575585
if !in_place.is_indirect() {
576586
for out_place in &*asm.outputs {
577587
if !out_place.is_indirect() && !in_place.is_indirect() {
578-
self.matrix.insert(in_place.local, out_place.local);
579-
self.matrix.insert(out_place.local, in_place.local);
588+
self.record_local_conflict(
589+
in_place.local,
590+
out_place.local,
591+
"aliasing llvm_asm! operands",
592+
);
580593
}
581594
}
582595
}
@@ -599,16 +612,22 @@ impl Conflicts<'a> {
599612
TerminatorKind::DropAndReplace { location, value, target: _, unwind: _ } => {
600613
if let Some(place) = value.place() {
601614
if !place.is_indirect() && !location.is_indirect() {
602-
self.matrix.insert(place.local, location.local);
603-
self.matrix.insert(location.local, place.local);
615+
self.record_local_conflict(
616+
place.local,
617+
location.local,
618+
"DropAndReplace operand overlap",
619+
);
604620
}
605621
}
606622
}
607623
TerminatorKind::Yield { value, resume: _, resume_arg, drop: _ } => {
608624
if let Some(place) = value.place() {
609625
if !place.is_indirect() && !resume_arg.is_indirect() {
610-
self.matrix.insert(place.local, resume_arg.local);
611-
self.matrix.insert(resume_arg.local, place.local);
626+
self.record_local_conflict(
627+
place.local,
628+
resume_arg.local,
629+
"Yield operand overlap",
630+
);
612631
}
613632
}
614633
}
@@ -623,8 +642,11 @@ impl Conflicts<'a> {
623642
for arg in args.iter().chain(Some(func)) {
624643
if let Some(place) = arg.place() {
625644
if !place.is_indirect() && !dest_place.is_indirect() {
626-
self.matrix.insert(dest_place.local, place.local);
627-
self.matrix.insert(place.local, dest_place.local);
645+
self.record_local_conflict(
646+
dest_place.local,
647+
place.local,
648+
"call dest/arg overlap",
649+
);
628650
}
629651
}
630652
}
@@ -653,8 +675,11 @@ impl Conflicts<'a> {
653675
InlineAsmOperand::In { reg: _, value } => {
654676
if let Some(p) = value.place() {
655677
if !p.is_indirect() && !dest_place.is_indirect() {
656-
self.matrix.insert(p.local, dest_place.local);
657-
self.matrix.insert(dest_place.local, p.local);
678+
self.record_local_conflict(
679+
p.local,
680+
dest_place.local,
681+
"asm! operand overlap",
682+
);
658683
}
659684
}
660685
}
@@ -664,8 +689,11 @@ impl Conflicts<'a> {
664689
place: Some(place),
665690
} => {
666691
if !place.is_indirect() && !dest_place.is_indirect() {
667-
self.matrix.insert(place.local, dest_place.local);
668-
self.matrix.insert(dest_place.local, place.local);
692+
self.record_local_conflict(
693+
place.local,
694+
dest_place.local,
695+
"asm! operand overlap",
696+
);
669697
}
670698
}
671699
InlineAsmOperand::InOut {
@@ -676,15 +704,21 @@ impl Conflicts<'a> {
676704
} => {
677705
if let Some(place) = in_value.place() {
678706
if !place.is_indirect() && !dest_place.is_indirect() {
679-
self.matrix.insert(place.local, dest_place.local);
680-
self.matrix.insert(dest_place.local, place.local);
707+
self.record_local_conflict(
708+
place.local,
709+
dest_place.local,
710+
"asm! operand overlap",
711+
);
681712
}
682713
}
683714

684715
if let Some(place) = out_place {
685716
if !place.is_indirect() && !dest_place.is_indirect() {
686-
self.matrix.insert(place.local, dest_place.local);
687-
self.matrix.insert(dest_place.local, place.local);
717+
self.record_local_conflict(
718+
place.local,
719+
dest_place.local,
720+
"asm! operand overlap",
721+
);
688722
}
689723
}
690724
}
@@ -750,6 +784,10 @@ impl Conflicts<'a> {
750784
// FIXME: This might be somewhat slow. Conflict graphs are undirected, maybe we can use
751785
// something with union-find to speed this up?
752786

787+
trace!("unify({:?}, {:?})", a, b);
788+
trace!("{:?} conflicts: {:?}", a, self.matrix.iter(a).format(", "));
789+
trace!("{:?} conflicts: {:?}", b, self.matrix.iter(b).format(", "));
790+
753791
// Make all locals that conflict with `a` also conflict with `b`, and vice versa.
754792
self.unify_cache.clear();
755793
for conflicts_with_a in self.matrix.iter(a) {

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