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sil: load [copy] affects reference counting #84333

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Merged
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Sep 17, 2025
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sil: load [copy] affects reference counting #84333

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6 changes: 3 additions & 3 deletions docs/SIL/Instructions.md
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Expand Up @@ -832,16 +832,16 @@ load-ownership-kind ::= 'take'
```

Loads the value at address `%0` from memory. `T` must be a loadable
type. This does not affect the reference count, if any, of the loaded
type. An unqualified load does not affect the reference count, if any, of the loaded
value; the value must be retained explicitly if necessary. It is
undefined behavior to load from uninitialized memory or to load from an
address that points to deallocated storage.

In OSSA the ownership kind specifies how to handle ownership:
- **trivial**: the loaded value is trivial and no further action must be taken
than to load the raw bits of the value
- **copy**: the loaded value is copied and the original value stays in the
memory location.
- **copy**: the loaded value is copied (e.g., retained) and the original value
stays in the memory location.
- **take**: the value is _moved_ from the memory location without copying.
After the `load`, the memory location remains uninitialized.

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9 changes: 8 additions & 1 deletion lib/SIL/Utils/InstructionUtils.cpp
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Expand Up @@ -552,7 +552,6 @@ RuntimeEffect swift::getRuntimeEffect(SILInstruction *inst, SILType &impactType)
case SILInstructionKind::CopyableToMoveOnlyWrapperValueInst:
case SILInstructionKind::MoveOnlyWrapperToCopyableValueInst:
case SILInstructionKind::UncheckedOwnershipConversionInst:
case SILInstructionKind::LoadInst:
case SILInstructionKind::LoadBorrowInst:
case SILInstructionKind::BeginBorrowInst:
case SILInstructionKind::BorrowedFromInst:
Expand Down Expand Up @@ -626,6 +625,14 @@ RuntimeEffect swift::getRuntimeEffect(SILInstruction *inst, SILType &impactType)
case SILInstructionKind::TypeValueInst:
case SILInstructionKind::IgnoredUseInst:
return RuntimeEffect::NoEffect;

case SILInstructionKind::LoadInst: {
if (cast<LoadInst>(inst)->getOwnershipQualifier() == LoadOwnershipQualifier::Copy) {
return ifNonTrivial(inst->getOperand(0)->getType(),
RuntimeEffect::RefCounting);
}
return RuntimeEffect::NoEffect;
}

case SILInstructionKind::OpenExistentialMetatypeInst:
case SILInstructionKind::OpenExistentialBoxInst:
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