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saethlinsaethlin
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Convert moves of references to copies in RefProp
1 parent 48aee7e commit cbe175f

12 files changed

+153
-47
lines changed

‎compiler/rustc_mir_transform/src/ref_prop.rs

Lines changed: 36 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -79,6 +79,7 @@ impl<'tcx> crate::MirPass<'tcx> for ReferencePropagation {
7979
#[instrument(level = "trace", skip(self, tcx, body))]
8080
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
8181
debug!(def_id = ?body.source.def_id());
82+
move_to_copy_pointers(tcx, body);
8283
while propagate_ssa(tcx, body) {}
8384
}
8485

@@ -87,11 +88,43 @@ impl<'tcx> crate::MirPass<'tcx> for ReferencePropagation {
8788
}
8889
}
8990

91+
/// The SSA analysis done by [`SsaLocals`] treats [`Operand::Move`] as a read, even though in
92+
/// general [`Operand::Move`] represents pass-by-pointer where the callee can overwrite the
93+
/// pointee (Miri always considers the place deinitialized). CopyProp has a similar trick to
94+
/// turn [`Operand::Move`] into [`Operand::Copy`] when required for an optimization, but in this
95+
/// pass we just turn all moves of pointers into copies because pointers should be by-value anyway.
96+
fn move_to_copy_pointers<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
97+
let mut visitor = MoveToCopyVisitor { tcx, local_decls: &body.local_decls };
98+
for (bb, data) in body.basic_blocks.as_mut_preserves_cfg().iter_enumerated_mut() {
99+
visitor.visit_basic_block_data(bb, data);
100+
}
101+
102+
struct MoveToCopyVisitor<'a, 'tcx> {
103+
tcx: TyCtxt<'tcx>,
104+
local_decls: &'a IndexVec<Local, LocalDecl<'tcx>>,
105+
}
106+
107+
impl<'a, 'tcx> MutVisitor<'tcx> for MoveToCopyVisitor<'a, 'tcx> {
108+
fn tcx(&self) -> TyCtxt<'tcx> {
109+
self.tcx
110+
}
111+
112+
fn visit_operand(&mut self, operand: &mut Operand<'tcx>, loc: Location) {
113+
if let Operand::Move(place) = *operand {
114+
if place.ty(self.local_decls, self.tcx).ty.is_any_ptr() {
115+
*operand = Operand::Copy(place);
116+
}
117+
}
118+
self.super_operand(operand, loc);
119+
}
120+
}
121+
}
122+
90123
fn propagate_ssa<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) -> bool {
91124
let typing_env = body.typing_env(tcx);
92125
let ssa = SsaLocals::new(tcx, body, typing_env);
93126

94-
let mut replacer = compute_replacement(tcx, body, &ssa);
127+
let mut replacer = compute_replacement(tcx, body, ssa);
95128
debug!(?replacer.targets);
96129
debug!(?replacer.allowed_replacements);
97130
debug!(?replacer.storage_to_remove);
@@ -119,7 +152,7 @@ enum Value<'tcx> {
119152
fn compute_replacement<'tcx>(
120153
tcx: TyCtxt<'tcx>,
121154
body: &Body<'tcx>,
122-
ssa: &SsaLocals,
155+
ssa: SsaLocals,
123156
) -> Replacer<'tcx> {
124157
let always_live_locals = always_storage_live_locals(body);
125158

@@ -138,7 +171,7 @@ fn compute_replacement<'tcx>(
138171
// reborrowed references.
139172
let mut storage_to_remove = DenseBitSet::new_empty(body.local_decls.len());
140173

141-
let fully_replaceable_locals = fully_replaceable_locals(ssa);
174+
let fully_replaceable_locals = fully_replaceable_locals(&ssa);
142175

143176
// Returns true iff we can use `place` as a pointee.
144177
//

‎tests/mir-opt/building/index_array_and_slice.rs

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -55,7 +55,7 @@ struct WithSliceTail(f64, [i32]);
5555
fn index_custom(custom: &WithSliceTail, index: usize) -> &i32 {
5656
// CHECK: bb0:
5757
// CHECK: [[PTR:_.+]] = &raw const (fake) ((*_1).1: [i32]);
58-
// CHECK: [[LEN:_.+]] = PtrMetadata(move [[PTR]]);
58+
// CHECK: [[LEN:_.+]] = PtrMetadata(copy [[PTR]]);
5959
// CHECK: [[LT:_.+]] = Lt(copy _2, copy [[LEN]]);
6060
// CHECK: assert(move [[LT]], "index out of bounds{{.+}}", move [[LEN]], copy _2) -> [success: bb1,
6161

‎tests/mir-opt/pre-codegen/issue_117368_print_invalid_constant.main.GVN.64bit.panic-unwind.diff

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -46,7 +46,7 @@
4646
StorageDead(_6);
4747
_4 = copy _5 as *mut [u8] (Transmute);
4848
StorageDead(_5);
49-
_3 = move _4 as *mut u8 (PtrToPtr);
49+
_3 = copy _4 as *mut u8 (PtrToPtr);
5050
StorageDead(_4);
5151
StorageDead(_3);
5252
- StorageDead(_1);

‎tests/mir-opt/pre-codegen/slice_index.slice_get_mut_usize.PreCodegen.after.panic-unwind.mir

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -30,7 +30,7 @@ fn slice_get_mut_usize(_1: &mut [u32], _2: usize) -> Option<&mut u32> {
3030
StorageDead(_3);
3131
StorageLive(_5);
3232
_5 = &mut (*_1)[_2];
33-
_0 = Option::<&mut u32>::Some(move _5);
33+
_0 = Option::<&mut u32>::Some(copy _5);
3434
StorageDead(_5);
3535
goto -> bb3;
3636
}

‎tests/mir-opt/reference_prop.debuginfo.ReferencePropagation.diff

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -99,7 +99,8 @@
9999
_13 = &(*_26);
100100
StorageLive(_15);
101101
_15 = RangeFull;
102-
_12 = <[i32; 10] as Index<RangeFull>>::index(move _13, move _15) -> [return: bb5, unwind continue];
102+
- _12 = <[i32; 10] as Index<RangeFull>>::index(move _13, move _15) -> [return: bb5, unwind continue];
103+
+ _12 = <[i32; 10] as Index<RangeFull>>::index(copy _13, move _15) -> [return: bb5, unwind continue];
103104
}
104105

105106
bb5: {

‎tests/mir-opt/reference_prop.reference_propagation.ReferencePropagation.diff

Lines changed: 12 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -218,8 +218,9 @@
218218
- StorageLive(_14);
219219
- _14 = &_11;
220220
- _13 = &(*_14);
221+
- _12 = move _13;
221222
+ _13 = &_11;
222-
_12 = move _13;
223+
+ _12 = copy _13;
223224
StorageDead(_13);
224225
- StorageDead(_14);
225226
StorageLive(_15);
@@ -252,7 +253,8 @@
252253
StorageLive(_23);
253254
StorageLive(_24);
254255
_24 = copy _21;
255-
_23 = opaque::<&&usize>(move _24) -> [return: bb3, unwind continue];
256+
- _23 = opaque::<&&usize>(move _24) -> [return: bb3, unwind continue];
257+
+ _23 = opaque::<&&usize>(copy _24) -> [return: bb3, unwind continue];
256258
}
257259

258260
bb3: {
@@ -276,7 +278,8 @@
276278
StorageLive(_30);
277279
StorageLive(_31);
278280
_31 = copy _28;
279-
_30 = opaque::<*mut &usize>(move _31) -> [return: bb4, unwind continue];
281+
- _30 = opaque::<*mut &usize>(move _31) -> [return: bb4, unwind continue];
282+
+ _30 = opaque::<*mut &usize>(copy _31) -> [return: bb4, unwind continue];
280283
}
281284

282285
bb4: {
@@ -299,7 +302,8 @@
299302
StorageLive(_36);
300303
StorageLive(_37);
301304
_37 = copy _34;
302-
_36 = opaque::<&usize>(move _37) -> [return: bb5, unwind continue];
305+
- _36 = opaque::<&usize>(move _37) -> [return: bb5, unwind continue];
306+
+ _36 = opaque::<&usize>(copy _37) -> [return: bb5, unwind continue];
303307
}
304308

305309
bb5: {
@@ -328,7 +332,8 @@
328332
StorageLive(_45);
329333
StorageLive(_46);
330334
_46 = copy _44;
331-
_45 = opaque::<&usize>(move _46) -> [return: bb6, unwind continue];
335+
- _45 = opaque::<&usize>(move _46) -> [return: bb6, unwind continue];
336+
+ _45 = opaque::<&usize>(copy _46) -> [return: bb6, unwind continue];
332337
}
333338

334339
bb6: {
@@ -368,8 +373,9 @@
368373
- StorageLive(_55);
369374
- _55 = &(*_1);
370375
- _54 = &(*_55);
376+
- _2 = move _54;
371377
+ _54 = &(*_1);
372-
_2 = move _54;
378+
+ _2 = copy _54;
373379
StorageDead(_54);
374380
- StorageDead(_55);
375381
StorageLive(_56);

‎tests/mir-opt/reference_prop.reference_propagation_const_ptr.ReferencePropagation.diff

Lines changed: 12 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -233,7 +233,8 @@
233233
_12 = &raw const _10;
234234
StorageLive(_13);
235235
_13 = &raw const _11;
236-
_12 = move _13;
236+
- _12 = move _13;
237+
+ _12 = copy _13;
237238
StorageDead(_13);
238239
StorageLive(_14);
239240
_14 = copy (*_12);
@@ -265,7 +266,8 @@
265266
StorageLive(_22);
266267
StorageLive(_23);
267268
_23 = copy _20;
268-
_22 = opaque::<&*const usize>(move _23) -> [return: bb3, unwind continue];
269+
- _22 = opaque::<&*const usize>(move _23) -> [return: bb3, unwind continue];
270+
+ _22 = opaque::<&*const usize>(copy _23) -> [return: bb3, unwind continue];
269271
}
270272

271273
bb3: {
@@ -289,7 +291,8 @@
289291
StorageLive(_29);
290292
StorageLive(_30);
291293
_30 = copy _27;
292-
_29 = opaque::<*mut *const usize>(move _30) -> [return: bb4, unwind continue];
294+
- _29 = opaque::<*mut *const usize>(move _30) -> [return: bb4, unwind continue];
295+
+ _29 = opaque::<*mut *const usize>(copy _30) -> [return: bb4, unwind continue];
293296
}
294297

295298
bb4: {
@@ -312,7 +315,8 @@
312315
StorageLive(_35);
313316
StorageLive(_36);
314317
_36 = copy _33;
315-
_35 = opaque::<*const usize>(move _36) -> [return: bb5, unwind continue];
318+
- _35 = opaque::<*const usize>(move _36) -> [return: bb5, unwind continue];
319+
+ _35 = opaque::<*const usize>(copy _36) -> [return: bb5, unwind continue];
316320
}
317321

318322
bb5: {
@@ -341,7 +345,8 @@
341345
StorageLive(_44);
342346
StorageLive(_45);
343347
_45 = copy _43;
344-
_44 = opaque::<*const usize>(move _45) -> [return: bb6, unwind continue];
348+
- _44 = opaque::<*const usize>(move _45) -> [return: bb6, unwind continue];
349+
+ _44 = opaque::<*const usize>(copy _45) -> [return: bb6, unwind continue];
345350
}
346351

347352
bb6: {
@@ -379,7 +384,8 @@
379384
_52 = &raw const (*_2);
380385
StorageLive(_53);
381386
_53 = &raw const (*_1);
382-
_2 = move _53;
387+
- _2 = move _53;
388+
+ _2 = copy _53;
383389
StorageDead(_53);
384390
StorageLive(_54);
385391
_54 = copy (*_52);

‎tests/mir-opt/reference_prop.reference_propagation_mut.ReferencePropagation.diff

Lines changed: 20 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -218,8 +218,9 @@
218218
- StorageLive(_14);
219219
- _14 = &mut _11;
220220
- _13 = &mut (*_14);
221+
- _12 = move _13;
221222
+ _13 = &mut _11;
222-
_12 = move _13;
223+
+ _12 = copy _13;
223224
StorageDead(_13);
224225
- StorageDead(_14);
225226
StorageLive(_15);
@@ -251,7 +252,8 @@
251252
StorageLive(_23);
252253
StorageLive(_24);
253254
_24 = copy _21;
254-
_23 = opaque::<&&mut usize>(move _24) -> [return: bb3, unwind continue];
255+
- _23 = opaque::<&&mut usize>(move _24) -> [return: bb3, unwind continue];
256+
+ _23 = opaque::<&&mut usize>(copy _24) -> [return: bb3, unwind continue];
255257
}
256258

257259
bb3: {
@@ -275,7 +277,8 @@
275277
StorageLive(_30);
276278
StorageLive(_31);
277279
_31 = copy _28;
278-
_30 = opaque::<*mut &mut usize>(move _31) -> [return: bb4, unwind continue];
280+
- _30 = opaque::<*mut &mut usize>(move _31) -> [return: bb4, unwind continue];
281+
+ _30 = opaque::<*mut &mut usize>(copy _31) -> [return: bb4, unwind continue];
279282
}
280283

281284
bb4: {
@@ -296,8 +299,10 @@
296299
_35 = copy (*_34);
297300
StorageLive(_36);
298301
StorageLive(_37);
299-
_37 = move _34;
300-
_36 = opaque::<&mut usize>(move _37) -> [return: bb5, unwind continue];
302+
- _37 = move _34;
303+
- _36 = opaque::<&mut usize>(move _37) -> [return: bb5, unwind continue];
304+
+ _37 = copy _34;
305+
+ _36 = opaque::<&mut usize>(copy _37) -> [return: bb5, unwind continue];
301306
}
302307

303308
bb5: {
@@ -316,15 +321,19 @@
316321
StorageLive(_41);
317322
_41 = copy (*_40);
318323
StorageLive(_42);
319-
_42 = move _40;
324+
- _42 = move _40;
325+
+ _42 = copy _40;
320326
StorageLive(_43);
321327
_43 = copy (*_42);
322328
StorageLive(_44);
323-
_44 = move _42;
329+
- _44 = move _42;
330+
+ _44 = copy _42;
324331
StorageLive(_45);
325332
StorageLive(_46);
326-
_46 = move _44;
327-
_45 = opaque::<&mut usize>(move _46) -> [return: bb6, unwind continue];
333+
- _46 = move _44;
334+
- _45 = opaque::<&mut usize>(move _46) -> [return: bb6, unwind continue];
335+
+ _46 = copy _44;
336+
+ _45 = opaque::<&mut usize>(copy _46) -> [return: bb6, unwind continue];
328337
}
329338

330339
bb6: {
@@ -364,8 +373,9 @@
364373
- StorageLive(_55);
365374
- _55 = &mut (*_1);
366375
- _54 = &mut (*_55);
376+
- _2 = move _54;
367377
+ _54 = &mut (*_1);
368-
_2 = move _54;
378+
+ _2 = copy _54;
369379
StorageDead(_54);
370380
- StorageDead(_55);
371381
StorageLive(_56);

‎tests/mir-opt/reference_prop.reference_propagation_mut_ptr.ReferencePropagation.diff

Lines changed: 12 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -214,7 +214,8 @@
214214
_12 = &raw mut _10;
215215
StorageLive(_13);
216216
_13 = &raw mut _11;
217-
_12 = move _13;
217+
- _12 = move _13;
218+
+ _12 = copy _13;
218219
StorageDead(_13);
219220
StorageLive(_14);
220221
_14 = copy (*_12);
@@ -245,7 +246,8 @@
245246
StorageLive(_22);
246247
StorageLive(_23);
247248
_23 = copy _20;
248-
_22 = opaque::<&*mut usize>(move _23) -> [return: bb3, unwind continue];
249+
- _22 = opaque::<&*mut usize>(move _23) -> [return: bb3, unwind continue];
250+
+ _22 = opaque::<&*mut usize>(copy _23) -> [return: bb3, unwind continue];
249251
}
250252

251253
bb3: {
@@ -269,7 +271,8 @@
269271
StorageLive(_29);
270272
StorageLive(_30);
271273
_30 = copy _27;
272-
_29 = opaque::<*mut *mut usize>(move _30) -> [return: bb4, unwind continue];
274+
- _29 = opaque::<*mut *mut usize>(move _30) -> [return: bb4, unwind continue];
275+
+ _29 = opaque::<*mut *mut usize>(copy _30) -> [return: bb4, unwind continue];
273276
}
274277

275278
bb4: {
@@ -291,7 +294,8 @@
291294
StorageLive(_35);
292295
StorageLive(_36);
293296
_36 = copy _33;
294-
_35 = opaque::<*mut usize>(move _36) -> [return: bb5, unwind continue];
297+
- _35 = opaque::<*mut usize>(move _36) -> [return: bb5, unwind continue];
298+
+ _35 = opaque::<*mut usize>(copy _36) -> [return: bb5, unwind continue];
295299
}
296300

297301
bb5: {
@@ -318,7 +322,8 @@
318322
StorageLive(_44);
319323
StorageLive(_45);
320324
_45 = copy _43;
321-
_44 = opaque::<*mut usize>(move _45) -> [return: bb6, unwind continue];
325+
- _44 = opaque::<*mut usize>(move _45) -> [return: bb6, unwind continue];
326+
+ _44 = opaque::<*mut usize>(copy _45) -> [return: bb6, unwind continue];
322327
}
323328

324329
bb6: {
@@ -356,7 +361,8 @@
356361
_52 = &raw mut (*_2);
357362
StorageLive(_53);
358363
_53 = &raw mut (*_1);
359-
_2 = move _53;
364+
- _2 = move _53;
365+
+ _2 = copy _53;
360366
StorageDead(_53);
361367
StorageLive(_54);
362368
_54 = copy (*_52);

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