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Auto merge of #105274 - saethlin:instcombine-mut-ref, r=cjgillot
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Enable instcombine for mutable reborrows

`instcombine` used to contain this comment, which is no longer accurate because there it is fine to copy `&mut _` in MIR:
```rust
// The dereferenced place must have type `&_`, so that we don't copy `&mut _`.
```
So let's try replacing that check with something much more permissive...
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@bors
bors committed Feb 17, 2023
2 parents 9aa5c24 + 1409cb5 commit 231bcd1
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Showing 4 changed files with 9 additions and 31 deletions.
6 changes: 1 addition & 5 deletions compiler/rustc_mir_transform/src/instcombine.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -110,11 +110,7 @@ impl<'tcx> InstCombineContext<'tcx, '_> {
fn combine_ref_deref(&self, source_info: &SourceInfo, rvalue: &mut Rvalue<'tcx>) {
if let Rvalue::Ref(_, _, place) = rvalue {
if let Some((base, ProjectionElem::Deref)) = place.as_ref().last_projection() {
if let ty::Ref(_, _, Mutability::Not) =
base.ty(self.local_decls, self.tcx).ty.kind()
{
// The dereferenced place must have type `&_`, so that we don't copy `&mut _`.
} else {
if rvalue.ty(self.local_decls, self.tcx) != base.ty(self.local_decls, self.tcx).ty {
return;
}

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10 changes: 2 additions & 8 deletions tests/mir-opt/funky_arms.float_to_exponential_common.ConstProp.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -86,16 +86,14 @@

bb6: {
_10 = ((_7 as Some).0: usize); // scope 3 at $DIR/funky_arms.rs:+13:17: +13:26
StorageLive(_11); // scope 3 at $DIR/funky_arms.rs:+15:43: +15:46
_11 = &mut (*_1); // scope 3 at $DIR/funky_arms.rs:+15:43: +15:46
StorageLive(_13); // scope 3 at $DIR/funky_arms.rs:+15:53: +15:57
_13 = _6; // scope 3 at $DIR/funky_arms.rs:+15:53: +15:57
StorageLive(_14); // scope 3 at $DIR/funky_arms.rs:+15:59: +15:79
StorageLive(_15); // scope 3 at $DIR/funky_arms.rs:+15:59: +15:75
_15 = _10 as u32 (IntToInt); // scope 3 at $DIR/funky_arms.rs:+15:59: +15:75
_14 = Add(move _15, const 1_u32); // scope 3 at $DIR/funky_arms.rs:+15:59: +15:79
StorageDead(_15); // scope 3 at $DIR/funky_arms.rs:+15:78: +15:79
_0 = float_to_exponential_common_exact::<T>(move _11, _2, move _13, move _14, _3) -> bb7; // scope 3 at $DIR/funky_arms.rs:+15:9: +15:87
_0 = float_to_exponential_common_exact::<T>(_1, _2, move _13, move _14, _3) -> bb7; // scope 3 at $DIR/funky_arms.rs:+15:9: +15:87
// mir::Constant
// + span: $DIR/funky_arms.rs:26:9: 26:42
// + literal: Const { ty: for<'a, 'b, 'c> fn(&'a mut Formatter<'b>, &'c T, Sign, u32, bool) -> Result<(), std::fmt::Error> {float_to_exponential_common_exact::<T>}, val: Value(<ZST>) }
Expand All @@ -104,24 +102,20 @@
bb7: {
StorageDead(_14); // scope 3 at $DIR/funky_arms.rs:+15:86: +15:87
StorageDead(_13); // scope 3 at $DIR/funky_arms.rs:+15:86: +15:87
StorageDead(_11); // scope 3 at $DIR/funky_arms.rs:+15:86: +15:87
goto -> bb10; // scope 2 at $DIR/funky_arms.rs:+13:5: +18:6
}

bb8: {
StorageLive(_18); // scope 2 at $DIR/funky_arms.rs:+17:46: +17:49
_18 = &mut (*_1); // scope 2 at $DIR/funky_arms.rs:+17:46: +17:49
StorageLive(_20); // scope 2 at $DIR/funky_arms.rs:+17:56: +17:60
_20 = _6; // scope 2 at $DIR/funky_arms.rs:+17:56: +17:60
_0 = float_to_exponential_common_shortest::<T>(move _18, _2, move _20, _3) -> bb9; // scope 2 at $DIR/funky_arms.rs:+17:9: +17:68
_0 = float_to_exponential_common_shortest::<T>(_1, _2, move _20, _3) -> bb9; // scope 2 at $DIR/funky_arms.rs:+17:9: +17:68
// mir::Constant
// + span: $DIR/funky_arms.rs:28:9: 28:45
// + literal: Const { ty: for<'a, 'b, 'c> fn(&'a mut Formatter<'b>, &'c T, Sign, bool) -> Result<(), std::fmt::Error> {float_to_exponential_common_shortest::<T>}, val: Value(<ZST>) }
}

bb9: {
StorageDead(_20); // scope 2 at $DIR/funky_arms.rs:+17:67: +17:68
StorageDead(_18); // scope 2 at $DIR/funky_arms.rs:+17:67: +17:68
goto -> bb10; // scope 2 at $DIR/funky_arms.rs:+13:5: +18:6
}

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6 changes: 1 addition & 5 deletions tests/mir-opt/inline/issue_58867_inline_as_ref_as_mut.a.Inline.after.mir
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Original file line number Diff line number Diff line change
Expand Up @@ -8,18 +8,14 @@ fn a(_1: &mut [T]) -> &mut [T] {
let mut _4: &mut [T]; // in scope 0 at $DIR/issue_58867_inline_as_ref_as_mut.rs:+1:5: +1:15
scope 1 (inlined <[T] as AsMut<[T]>>::as_mut) { // at $DIR/issue_58867_inline_as_ref_as_mut.rs:3:7: 3:15
debug self => _4; // in scope 1 at $SRC_DIR/core/src/convert/mod.rs:LL:COL
let mut _5: &mut [T]; // in scope 1 at $SRC_DIR/core/src/convert/mod.rs:LL:COL
}

bb0: {
StorageLive(_2); // scope 0 at $DIR/issue_58867_inline_as_ref_as_mut.rs:+1:5: +1:15
StorageLive(_3); // scope 0 at $DIR/issue_58867_inline_as_ref_as_mut.rs:+1:5: +1:15
StorageLive(_4); // scope 0 at $DIR/issue_58867_inline_as_ref_as_mut.rs:+1:5: +1:15
_4 = &mut (*_1); // scope 0 at $DIR/issue_58867_inline_as_ref_as_mut.rs:+1:5: +1:15
StorageLive(_5); // scope 1 at $SRC_DIR/core/src/convert/mod.rs:LL:COL
_5 = &mut (*_4); // scope 1 at $SRC_DIR/core/src/convert/mod.rs:LL:COL
_3 = &mut (*_5); // scope 1 at $SRC_DIR/core/src/convert/mod.rs:LL:COL
StorageDead(_5); // scope 1 at $SRC_DIR/core/src/convert/mod.rs:LL:COL
_3 = _4; // scope 1 at $SRC_DIR/core/src/convert/mod.rs:LL:COL
_2 = &mut (*_3); // scope 0 at $DIR/issue_58867_inline_as_ref_as_mut.rs:+1:5: +1:15
StorageDead(_4); // scope 0 at $DIR/issue_58867_inline_as_ref_as_mut.rs:+1:14: +1:15
_0 = &mut (*_2); // scope 0 at $DIR/issue_58867_inline_as_ref_as_mut.rs:+1:5: +1:15
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18 changes: 5 additions & 13 deletions tests/mir-opt/inline/issue_58867_inline_as_ref_as_mut.b.Inline.after.mir
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Original file line number Diff line number Diff line change
Expand Up @@ -8,26 +8,18 @@ fn b(_1: &mut Box<T>) -> &mut T {
let mut _4: &mut std::boxed::Box<T>; // in scope 0 at $DIR/issue_58867_inline_as_ref_as_mut.rs:+1:5: +1:15
scope 1 (inlined <Box<T> as AsMut<T>>::as_mut) { // at $DIR/issue_58867_inline_as_ref_as_mut.rs:8:7: 8:15
debug self => _4; // in scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
let mut _5: &mut T; // in scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
let mut _6: &mut T; // in scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
let mut _7: std::boxed::Box<T>; // in scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
let mut _8: *const T; // in scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
let mut _5: std::boxed::Box<T>; // in scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
let mut _6: *const T; // in scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
}

bb0: {
StorageLive(_2); // scope 0 at $DIR/issue_58867_inline_as_ref_as_mut.rs:+1:5: +1:15
StorageLive(_3); // scope 0 at $DIR/issue_58867_inline_as_ref_as_mut.rs:+1:5: +1:15
StorageLive(_4); // scope 0 at $DIR/issue_58867_inline_as_ref_as_mut.rs:+1:5: +1:15
_4 = &mut (*_1); // scope 0 at $DIR/issue_58867_inline_as_ref_as_mut.rs:+1:5: +1:15
StorageLive(_5); // scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
StorageLive(_6); // scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
_7 = deref_copy (*_4); // scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
_8 = (((_7.0: std::ptr::Unique<T>).0: std::ptr::NonNull<T>).0: *const T); // scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
_6 = &mut (*_8); // scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
_5 = &mut (*_6); // scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
_3 = &mut (*_5); // scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
StorageDead(_6); // scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
StorageDead(_5); // scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
_5 = deref_copy (*_4); // scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
_6 = (((_5.0: std::ptr::Unique<T>).0: std::ptr::NonNull<T>).0: *const T); // scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
_3 = &mut (*_6); // scope 1 at $SRC_DIR/alloc/src/boxed.rs:LL:COL
_2 = &mut (*_3); // scope 0 at $DIR/issue_58867_inline_as_ref_as_mut.rs:+1:5: +1:15
StorageDead(_4); // scope 0 at $DIR/issue_58867_inline_as_ref_as_mut.rs:+1:14: +1:15
_0 = &mut (*_2); // scope 0 at $DIR/issue_58867_inline_as_ref_as_mut.rs:+1:5: +1:15
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