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Disable a silcombine pattern that creates unoptimizable copies #70440

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Merged
merged 1 commit into from
Dec 14, 2023
Merged

Disable a silcombine pattern that creates unoptimizable copies #70440

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30 changes: 3 additions & 27 deletions lib/SILOptimizer/SILCombiner/SILCombinerCastVisitors.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -800,37 +800,13 @@ SILCombiner::visitRawPointerToRefInst(RawPointerToRefInst *rawToRef) {
// ->
// (unchecked_ref_cast x X->Z)
if (auto *refToRaw = dyn_cast<RefToRawPointerInst>(rawToRef->getOperand())) {
// We do this optimization only in non-ossa.
// In ossa, the copy created by ossa rauw is unoptimizable, skipping for
// this reason.
if (!hasOwnership()) {
return Builder.createUncheckedRefCast(
rawToRef->getLoc(), refToRaw->getOperand(), rawToRef->getType());
}

// raw_pointer_to_ref produces an unowned value. So we need to handle it
// especially with ownership.
{
SILValue originalRef = refToRaw->getOperand();
OwnershipRAUWHelper helper(ownershipFixupContext, rawToRef, originalRef);
if (helper) {
// Since we are using std::next, we use getAutogeneratedLocation to
// avoid any issues if our next insertion point is a terminator.
auto loc = RegularLocation::getAutoGeneratedLocation();
auto replacement = helper.prepareReplacement();
auto *newInst = Builder.createUncheckedRefCast(
loc, replacement, rawToRef->getType());
// If we have an operand with ownership, we need to change our
// unchecked_ref_cast to produce an unowned value. This is because
// otherwise, our unchecked_ref_cast will consume the underlying owned
// value, changing a BitwiseEscape to a LifetimeEnding use?! In
// contrast, for guaranteed, we are replacing a BitwiseEscape use
// (ref_to_rawpointer) with a ForwardedBorrowingUse (unchecked_ref_cast)
// which is safe.
if (newInst->getForwardingOwnershipKind() == OwnershipKind::Owned) {
newInst->setForwardingOwnershipKind(OwnershipKind::Unowned);
}
helper.perform(newInst);
return nullptr;
}
}
}

return nullptr;
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21 changes: 6 additions & 15 deletions test/SILOptimizer/sil_combine_ossa.sil
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Original file line number Diff line number Diff line change
Expand Up @@ -1572,11 +1572,8 @@ bb0(%0 : @owned $B):

// CHECK-LABEL: sil [ossa] @unchecked_ref_cast_formation_owned : $@convention(thin) (@owned B) -> @owned F {
// CHECK: bb0([[INPUT_REF:%[0-9]+]] : @owned $B):
// CHECK-NOT: ref_to_raw_pointer
// CHECK-NOT: raw_pointer_to_ref
// CHECK: unchecked_ref_cast
// CHECK-NOT: ref_to_raw_pointer
// CHECK-NOT: raw_pointer_to_ref
// CHECK: ref_to_raw_pointer
// CHECK: raw_pointer_to_ref
// CHECK: } // end sil function 'unchecked_ref_cast_formation_owned'
sil [ossa] @unchecked_ref_cast_formation_owned : $@convention(thin) (@owned B) -> @owned F {
bb0(%0 : @owned $B):
Expand All @@ -1589,11 +1586,8 @@ bb0(%0 : @owned $B):

// CHECK-LABEL: sil [ossa] @unchecked_ref_cast_formation_guaranteed : $@convention(thin) (@guaranteed B) -> @owned F {
// CHECK: bb0([[INPUT_REF:%[0-9]+]] : @guaranteed $B):
// CHECK-NOT: ref_to_raw_pointer
// CHECK-NOT: raw_pointer_to_ref
// CHECK: unchecked_ref_cast
// CHECK-NOT: ref_to_raw_pointer
// CHECK-NOT: raw_pointer_to_ref
// CHECK: ref_to_raw_pointer
// CHECK: raw_pointer_to_ref
// CHECK: } // end sil function 'unchecked_ref_cast_formation_guaranteed'
sil [ossa] @unchecked_ref_cast_formation_guaranteed : $@convention(thin) (@guaranteed B) -> @owned F {
bb0(%0 : @guaranteed $B):
Expand All @@ -1605,11 +1599,8 @@ bb0(%0 : @guaranteed $B):

// CHECK-LABEL: sil [ossa] @unchecked_ref_cast_formation_unowned : $@convention(thin) (B) -> F {
// CHECK: bb0([[INPUT_REF:%[0-9]+]] :
// CHECK-NOT: ref_to_raw_pointer
// CHECK-NOT: raw_pointer_to_ref
// CHECK: unchecked_ref_cast
// CHECK-NOT: ref_to_raw_pointer
// CHECK-NOT: raw_pointer_to_ref
// CHECK: ref_to_raw_pointer
// CHECK: raw_pointer_to_ref
// CHECK: } // end sil function 'unchecked_ref_cast_formation_unowned'
sil [ossa] @unchecked_ref_cast_formation_unowned : $@convention(thin) (B) -> F {
bb0(%0 : @unowned $B):
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