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‎src/librustc_mir/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

@@ -521,7 +525,7 @@ impl Conflicts<'a> {
521525

522526
trace!("record conflicts at {:?}", loc);
523527

524-
this.record_conflicts(&mut live_and_init_locals[statement_index]);
528+
this.record_dataflow_conflicts(&mut live_and_init_locals[statement_index]);
525529
}
526530

527531
init.seek_to_block_end(block);
@@ -530,13 +534,13 @@ impl Conflicts<'a> {
530534
conflicts.intersect(live.get());
531535
trace!("record conflicts at end of {:?}", block);
532536

533-
this.record_conflicts(&mut conflicts);
537+
this.record_dataflow_conflicts(&mut conflicts);
534538
}
535539

536540
this
537541
}
538542

539-
fn record_conflicts(&mut self, new_conflicts: &mut BitSet<Local>) {
543+
fn record_dataflow_conflicts(&mut self, new_conflicts: &mut BitSet<Local>) {
540544
// Remove all locals that are not candidates.
541545
new_conflicts.intersect(self.relevant_locals);
542546

@@ -545,6 +549,12 @@ impl Conflicts<'a> {
545549
}
546550
}
547551

552+
fn record_local_conflict(&mut self, a: Local, b: Local, why: &str) {
553+
trace!("conflict {:?} <-> {:?} due to {}", a, b, why);
554+
self.matrix.insert(a, b);
555+
self.matrix.insert(b, a);
556+
}
557+
548558
/// Records locals that must not overlap during the evaluation of `stmt`. These locals conflict
549559
/// and must not be merged.
550560
fn record_statement_conflicts(&mut self, stmt: &Statement<'_>) {
@@ -561,8 +571,11 @@ impl Conflicts<'a> {
561571
if !in_place.is_indirect() {
562572
for out_place in &*asm.outputs {
563573
if !out_place.is_indirect() && !in_place.is_indirect() {
564-
self.matrix.insert(in_place.local, out_place.local);
565-
self.matrix.insert(out_place.local, in_place.local);
574+
self.record_local_conflict(
575+
in_place.local,
576+
out_place.local,
577+
"aliasing llvm_asm! operands",
578+
);
566579
}
567580
}
568581
}
@@ -585,16 +598,22 @@ impl Conflicts<'a> {
585598
TerminatorKind::DropAndReplace { location, value, target: _, unwind: _ } => {
586599
if let Some(place) = value.place() {
587600
if !place.is_indirect() && !location.is_indirect() {
588-
self.matrix.insert(place.local, location.local);
589-
self.matrix.insert(location.local, place.local);
601+
self.record_local_conflict(
602+
place.local,
603+
location.local,
604+
"DropAndReplace operand overlap",
605+
);
590606
}
591607
}
592608
}
593609
TerminatorKind::Yield { value, resume: _, resume_arg, drop: _ } => {
594610
if let Some(place) = value.place() {
595611
if !place.is_indirect() && !resume_arg.is_indirect() {
596-
self.matrix.insert(place.local, resume_arg.local);
597-
self.matrix.insert(resume_arg.local, place.local);
612+
self.record_local_conflict(
613+
place.local,
614+
resume_arg.local,
615+
"Yield operand overlap",
616+
);
598617
}
599618
}
600619
}
@@ -609,8 +628,11 @@ impl Conflicts<'a> {
609628
for arg in args.iter().chain(Some(func)) {
610629
if let Some(place) = arg.place() {
611630
if !place.is_indirect() && !dest_place.is_indirect() {
612-
self.matrix.insert(dest_place.local, place.local);
613-
self.matrix.insert(place.local, dest_place.local);
631+
self.record_local_conflict(
632+
dest_place.local,
633+
place.local,
634+
"call dest/arg overlap",
635+
);
614636
}
615637
}
616638
}
@@ -639,8 +661,11 @@ impl Conflicts<'a> {
639661
InlineAsmOperand::In { reg: _, value } => {
640662
if let Some(p) = value.place() {
641663
if !p.is_indirect() && !dest_place.is_indirect() {
642-
self.matrix.insert(p.local, dest_place.local);
643-
self.matrix.insert(dest_place.local, p.local);
664+
self.record_local_conflict(
665+
p.local,
666+
dest_place.local,
667+
"asm! operand overlap",
668+
);
644669
}
645670
}
646671
}
@@ -650,8 +675,11 @@ impl Conflicts<'a> {
650675
place: Some(place),
651676
} => {
652677
if !place.is_indirect() && !dest_place.is_indirect() {
653-
self.matrix.insert(place.local, dest_place.local);
654-
self.matrix.insert(dest_place.local, place.local);
678+
self.record_local_conflict(
679+
place.local,
680+
dest_place.local,
681+
"asm! operand overlap",
682+
);
655683
}
656684
}
657685
InlineAsmOperand::InOut {
@@ -662,15 +690,21 @@ impl Conflicts<'a> {
662690
} => {
663691
if let Some(place) = in_value.place() {
664692
if !place.is_indirect() && !dest_place.is_indirect() {
665-
self.matrix.insert(place.local, dest_place.local);
666-
self.matrix.insert(dest_place.local, place.local);
693+
self.record_local_conflict(
694+
place.local,
695+
dest_place.local,
696+
"asm! operand overlap",
697+
);
667698
}
668699
}
669700

670701
if let Some(place) = out_place {
671702
if !place.is_indirect() && !dest_place.is_indirect() {
672-
self.matrix.insert(place.local, dest_place.local);
673-
self.matrix.insert(dest_place.local, place.local);
703+
self.record_local_conflict(
704+
place.local,
705+
dest_place.local,
706+
"asm! operand overlap",
707+
);
674708
}
675709
}
676710
}
@@ -736,6 +770,10 @@ impl Conflicts<'a> {
736770
// FIXME: This might be somewhat slow. Conflict graphs are undirected, maybe we can use
737771
// something with union-find to speed this up?
738772

773+
trace!("unify({:?}, {:?})", a, b);
774+
trace!("{:?} conflicts: {:?}", a, self.matrix.iter(a).format(", "));
775+
trace!("{:?} conflicts: {:?}", b, self.matrix.iter(b).format(", "));
776+
739777
// Make all locals that conflict with `a` also conflict with `b`, and vice versa.
740778
self.unify_cache.clear();
741779
for conflicts_with_a in self.matrix.iter(a) {

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