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cjgillotcjgillot
committedJun 28, 2024·
Propagate places through assignments.
1 parent 0366b96 commit 845d318

13 files changed

+177
-33
lines changed
 

‎compiler/rustc_mir_dataflow/src/value_analysis.rs

Lines changed: 109 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -36,7 +36,7 @@ use std::fmt::{Debug, Formatter};
3636
use std::ops::Range;
3737

3838
use rustc_data_structures::captures::Captures;
39-
use rustc_data_structures::fx::FxHashMap;
39+
use rustc_data_structures::fx::{FxHashMap, FxIndexSet};
4040
use rustc_data_structures::stack::ensure_sufficient_stack;
4141
use rustc_index::bit_set::BitSet;
4242
use rustc_index::{IndexSlice, IndexVec};
@@ -760,7 +760,52 @@ impl<'tcx> Map<'tcx> {
760760
tracing::trace!(?local, ?place);
761761
}
762762

763-
PlaceCollector { tcx, body, map: self }.visit_body(body);
763+
// Collect syntactic places and assignments between them.
764+
let mut collector =
765+
PlaceCollector { tcx, body, map: self, assignments: Default::default() };
766+
collector.visit_body(body);
767+
let PlaceCollector { mut assignments, .. } = collector;
768+
769+
// Just collecting syntactic places is not enough. We may need to propagate this pattern:
770+
// _1 = (const 5u32, const 13i64);
771+
// _2 = _1;
772+
// _3 = (_2.0 as u32);
773+
//
774+
// `_1.0` does not appear, but we still need to track it. This is achieved by propagating
775+
// projections from assignments. We recorded an assignment between `_2` and `_1`, so we
776+
// want `_1` and `_2` to have the same sub-places.
777+
//
778+
// This is what this fixpoint loop does. While we are still creating places, run through
779+
// all the assignments, and register places for children.
780+
let mut num_places = 0;
781+
while num_places < self.places.len() {
782+
num_places = self.places.len();
783+
784+
for assign in 0.. {
785+
let Some(&(lhs, rhs)) = assignments.get_index(assign) else { break };
786+
787+
// Mirror children from `lhs` in `rhs`.
788+
let mut child = self.places[lhs].first_child;
789+
while let Some(lhs_child) = child {
790+
let PlaceInfo { ty, proj_elem, next_sibling, .. } = self.places[lhs_child];
791+
let rhs_child =
792+
self.register_place(ty, rhs, proj_elem.expect("child is not a projection"));
793+
assignments.insert((lhs_child, rhs_child));
794+
child = next_sibling;
795+
}
796+
797+
// Conversely, mirror children from `rhs` in `lhs`.
798+
let mut child = self.places[rhs].first_child;
799+
while let Some(rhs_child) = child {
800+
let PlaceInfo { ty, proj_elem, next_sibling, .. } = self.places[rhs_child];
801+
let lhs_child =
802+
self.register_place(ty, lhs, proj_elem.expect("child is not a projection"));
803+
assignments.insert((lhs_child, rhs_child));
804+
child = next_sibling;
805+
}
806+
}
807+
}
808+
drop(assignments);
764809

765810
// Create values for places whose type have scalar layout.
766811
let param_env = tcx.param_env_reveal_all_normalized(body.source.def_id());
@@ -845,17 +890,14 @@ struct PlaceCollector<'a, 'b, 'tcx> {
845890
tcx: TyCtxt<'tcx>,
846891
body: &'b Body<'tcx>,
847892
map: &'a mut Map<'tcx>,
893+
assignments: FxIndexSet<(PlaceIndex, PlaceIndex)>,
848894
}
849895

850-
impl<'tcx> Visitor<'tcx> for PlaceCollector<'_, '_, 'tcx> {
896+
impl<'tcx> PlaceCollector<'_, '_, 'tcx> {
851897
#[tracing::instrument(level = "trace", skip(self))]
852-
fn visit_place(&mut self, place: &Place<'tcx>, ctxt: PlaceContext, _: Location) {
853-
if !ctxt.is_use() {
854-
return;
855-
}
856-
898+
fn register_place(&mut self, place: Place<'tcx>) -> Option<PlaceIndex> {
857899
// Create a place for this projection.
858-
let Some(mut place_index) = self.map.locals[place.local] else { return };
900+
let mut place_index = self.map.locals[place.local]?;
859901
let mut ty = PlaceTy::from_ty(self.body.local_decls[place.local].ty);
860902
tracing::trace!(?place_index, ?ty);
861903

@@ -869,7 +911,7 @@ impl<'tcx> Visitor<'tcx> for PlaceCollector<'_, '_, 'tcx> {
869911
}
870912

871913
for proj in place.projection {
872-
let Ok(track_elem) = proj.try_into() else { return };
914+
let track_elem = proj.try_into().ok()?;
873915
ty = ty.projection_ty(self.tcx, proj);
874916
place_index = self.map.register_place(ty.ty, place_index, track_elem);
875917
tracing::trace!(?proj, ?place_index, ?ty);
@@ -883,6 +925,63 @@ impl<'tcx> Visitor<'tcx> for PlaceCollector<'_, '_, 'tcx> {
883925
self.map.register_place(discriminant_ty, place_index, TrackElem::Discriminant);
884926
}
885927
}
928+
929+
Some(place_index)
930+
}
931+
}
932+
933+
impl<'tcx> Visitor<'tcx> for PlaceCollector<'_, '_, 'tcx> {
934+
#[tracing::instrument(level = "trace", skip(self))]
935+
fn visit_place(&mut self, place: &Place<'tcx>, ctxt: PlaceContext, _: Location) {
936+
if !ctxt.is_use() {
937+
return;
938+
}
939+
940+
self.register_place(*place);
941+
}
942+
943+
fn visit_assign(&mut self, lhs: &Place<'tcx>, rhs: &Rvalue<'tcx>, location: Location) {
944+
self.super_assign(lhs, rhs, location);
945+
946+
match rhs {
947+
Rvalue::Use(Operand::Move(rhs) | Operand::Copy(rhs)) | Rvalue::CopyForDeref(rhs) => {
948+
let Some(lhs) = self.register_place(*lhs) else { return };
949+
let Some(rhs) = self.register_place(*rhs) else { return };
950+
self.assignments.insert((lhs, rhs));
951+
}
952+
Rvalue::Aggregate(kind, fields) => {
953+
let Some(mut lhs) = self.register_place(*lhs) else { return };
954+
match **kind {
955+
// Do not propagate unions.
956+
AggregateKind::Adt(_, _, _, _, Some(_)) => return,
957+
AggregateKind::Adt(_, variant, _, _, None) => {
958+
let ty = self.map.places[lhs].ty;
959+
if ty.is_enum() {
960+
lhs = self.map.register_place(ty, lhs, TrackElem::Variant(variant));
961+
}
962+
}
963+
AggregateKind::RawPtr(..)
964+
| AggregateKind::Array(_)
965+
| AggregateKind::Tuple
966+
| AggregateKind::Closure(..)
967+
| AggregateKind::Coroutine(..)
968+
| AggregateKind::CoroutineClosure(..) => {}
969+
}
970+
for (index, field) in fields.iter_enumerated() {
971+
if let Some(rhs) = field.place()
972+
&& let Some(rhs) = self.register_place(rhs)
973+
{
974+
let lhs = self.map.register_place(
975+
self.map.places[rhs].ty,
976+
lhs,
977+
TrackElem::Field(index),
978+
);
979+
self.assignments.insert((lhs, rhs));
980+
}
981+
}
982+
}
983+
_ => {}
984+
}
886985
}
887986
}
888987

‎tests/mir-opt/dataflow-const-prop/aggregate_copy.foo.DataflowConstProp.diff

Lines changed: 16 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -22,19 +22,25 @@
2222
StorageLive(_1);
2323
_1 = const Foo;
2424
StorageLive(_2);
25-
_2 = _1;
25+
- _2 = _1;
26+
+ _2 = const (5_u32, 3_u32);
2627
StorageLive(_3);
27-
_3 = (_2.1: u32);
28+
- _3 = (_2.1: u32);
29+
+ _3 = const 3_u32;
2830
StorageLive(_4);
2931
StorageLive(_5);
30-
_5 = _3;
31-
_4 = Ge(move _5, const 2_u32);
32-
switchInt(move _4) -> [0: bb2, otherwise: bb1];
32+
- _5 = _3;
33+
- _4 = Ge(move _5, const 2_u32);
34+
- switchInt(move _4) -> [0: bb2, otherwise: bb1];
35+
+ _5 = const 3_u32;
36+
+ _4 = const true;
37+
+ switchInt(const true) -> [0: bb2, otherwise: bb1];
3338
}
3439

3540
bb1: {
3641
StorageDead(_5);
37-
_0 = (_2.0: u32);
42+
- _0 = (_2.0: u32);
43+
+ _0 = const 5_u32;
3844
goto -> bb3;
3945
}
4046

@@ -51,5 +57,9 @@
5157
StorageDead(_1);
5258
return;
5359
}
60+
+ }
61+
+
62+
+ ALLOC0 (size: 8, align: 4) {
63+
+ 05 00 00 00 03 00 00 00 │ ........
5464
}
5565

‎tests/mir-opt/dataflow-const-prop/aggregate_copy.rs

Lines changed: 6 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -12,12 +12,14 @@ fn foo() -> u32 {
1212

1313
// CHECK:bb0: {
1414
// CHECK: [[a]] = const Foo;
15-
// CHECK: [[b]] = [[a]];
16-
// CHECK: [[c]] = ([[b]].1: u32);
17-
// CHECK: switchInt(move {{_.*}}) -> [0: bb2, otherwise: bb1];
15+
// CHECK: [[b]] = const (5_u32, 3_u32);
16+
// CHECK: [[c]] = const 3_u32;
17+
// CHECK: {{_.*}} = const 3_u32;
18+
// CHECK: {{_.*}} = const true;
19+
// CHECK: switchInt(const true) -> [0: bb2, otherwise: bb1];
1820

1921
// CHECK:bb1: {
20-
// CHECK: _0 = ([[b]].0: u32);
22+
// CHECK: _0 = const 5_u32;
2123
// CHECK: goto -> bb3;
2224

2325
// CHECK:bb2: {

‎tests/mir-opt/dataflow-const-prop/repr_transparent.main.DataflowConstProp.diff

Lines changed: 5 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -32,7 +32,7 @@
3232
StorageDead(_5);
3333
StorageDead(_4);
3434
- _2 = I32(move _3);
35-
+ _2 = I32(const 0_i32);
35+
+ _2 = const I32(0_i32);
3636
StorageDead(_3);
3737
_0 = const ();
3838
StorageDead(_2);
@@ -42,6 +42,10 @@
4242
+ }
4343
+
4444
+ ALLOC0 (size: 4, align: 4) {
45+
+ 00 00 00 00 │ ....
46+
+ }
47+
+
48+
+ ALLOC1 (size: 4, align: 4) {
4549
+ 00 00 00 00 │ ....
4650
}
4751

‎tests/mir-opt/dataflow-const-prop/repr_transparent.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -15,6 +15,6 @@ fn main() {
1515
// CHECK: [[x]] = const I32(0_i32);
1616
let x = I32(0);
1717

18-
// CHECK: [[y]] = I32(const 0_i32);
18+
// CHECK: [[y]] = const I32(0_i32);
1919
let y = I32(x.0 + x.0);
2020
}

‎tests/mir-opt/dataflow-const-prop/transmute.less_as_i8.DataflowConstProp.32bit.diff

Lines changed: 12 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -7,10 +7,20 @@
77

88
bb0: {
99
StorageLive(_1);
10-
_1 = Less;
11-
_0 = move _1 as i8 (Transmute);
10+
- _1 = Less;
11+
- _0 = move _1 as i8 (Transmute);
12+
+ _1 = const Less;
13+
+ _0 = const std::cmp::Ordering::Less as i8 (Transmute);
1214
StorageDead(_1);
1315
return;
1416
}
17+
+ }
18+
+
19+
+ ALLOC0 (size: 1, align: 1) {
20+
+ ff │ .
21+
+ }
22+
+
23+
+ ALLOC1 (size: 1, align: 1) {
24+
+ ff │ .
1525
}
1626

‎tests/mir-opt/dataflow-const-prop/transmute.less_as_i8.DataflowConstProp.64bit.diff

Lines changed: 12 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -7,10 +7,20 @@
77

88
bb0: {
99
StorageLive(_1);
10-
_1 = Less;
11-
_0 = move _1 as i8 (Transmute);
10+
- _1 = Less;
11+
- _0 = move _1 as i8 (Transmute);
12+
+ _1 = const Less;
13+
+ _0 = const std::cmp::Ordering::Less as i8 (Transmute);
1214
StorageDead(_1);
1315
return;
1416
}
17+
+ }
18+
+
19+
+ ALLOC0 (size: 1, align: 1) {
20+
+ ff │ .
21+
+ }
22+
+
23+
+ ALLOC1 (size: 1, align: 1) {
24+
+ ff │ .
1525
}
1626

‎tests/mir-opt/dataflow-const-prop/tuple.main.DataflowConstProp.32bit.diff

Lines changed: 5 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -81,7 +81,7 @@
8181
- _14 = _6;
8282
- _11 = (move _12, move _13, move _14);
8383
+ _14 = const 11_i32;
84-
+ _11 = (const 6_i32, move _13, const 11_i32);
84+
+ _11 = (const 6_i32, const (2_i32, 3_i32), const 11_i32);
8585
StorageDead(_14);
8686
StorageDead(_13);
8787
StorageDead(_12);
@@ -103,6 +103,10 @@
103103
+ }
104104
+
105105
+ ALLOC2 (size: 8, align: 4) {
106+
+ 02 00 00 00 03 00 00 00 │ ........
107+
+ }
108+
+
109+
+ ALLOC3 (size: 8, align: 4) {
106110
+ 01 00 00 00 02 00 00 00 │ ........
107111
}
108112

‎tests/mir-opt/dataflow-const-prop/tuple.main.DataflowConstProp.64bit.diff

Lines changed: 5 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -81,7 +81,7 @@
8181
- _14 = _6;
8282
- _11 = (move _12, move _13, move _14);
8383
+ _14 = const 11_i32;
84-
+ _11 = (const 6_i32, move _13, const 11_i32);
84+
+ _11 = (const 6_i32, const (2_i32, 3_i32), const 11_i32);
8585
StorageDead(_14);
8686
StorageDead(_13);
8787
StorageDead(_12);
@@ -103,6 +103,10 @@
103103
+ }
104104
+
105105
+ ALLOC2 (size: 8, align: 4) {
106+
+ 02 00 00 00 03 00 00 00 │ ........
107+
+ }
108+
+
109+
+ ALLOC3 (size: 8, align: 4) {
106110
+ 01 00 00 00 02 00 00 00 │ ........
107111
}
108112

‎tests/mir-opt/dataflow-const-prop/tuple.rs

Lines changed: 1 addition & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -22,7 +22,6 @@ fn main() {
2222
// CHECK: [[c]] = const 11_i32;
2323
let c = a.0 + a.1 + b;
2424

25-
// CHECK: [[a2:_.*]] = const (2_i32, 3_i32);
26-
// CHECK: [[d]] = (const 6_i32, move [[a2]], const 11_i32);
25+
// CHECK: [[d]] = (const 6_i32, const (2_i32, 3_i32), const 11_i32);
2726
let d = (b, a, c);
2827
}

‎tests/mir-opt/jump_threading.aggregate_copy.JumpThreading.panic-abort.diff

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -29,7 +29,8 @@
2929
StorageLive(_5);
3030
_5 = _3;
3131
_4 = Eq(move _5, const 2_u32);
32-
switchInt(move _4) -> [0: bb2, otherwise: bb1];
32+
- switchInt(move _4) -> [0: bb2, otherwise: bb1];
33+
+ goto -> bb2;
3334
}
3435

3536
bb1: {

‎tests/mir-opt/jump_threading.aggregate_copy.JumpThreading.panic-unwind.diff

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -29,7 +29,8 @@
2929
StorageLive(_5);
3030
_5 = _3;
3131
_4 = Eq(move _5, const 2_u32);
32-
switchInt(move _4) -> [0: bb2, otherwise: bb1];
32+
- switchInt(move _4) -> [0: bb2, otherwise: bb1];
33+
+ goto -> bb2;
3334
}
3435

3536
bb1: {

‎tests/mir-opt/jump_threading.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -509,7 +509,7 @@ fn assume(a: u8, b: bool) -> u8 {
509509
/// Verify that jump threading succeeds seeing through copies of aggregates.
510510
fn aggregate_copy() -> u32 {
511511
// CHECK-LABEL: fn aggregate_copy(
512-
// CHECK: switchInt(
512+
// CHECK-NOT: switchInt(
513513

514514
const Foo: (u32, u32) = (5, 3);
515515

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