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StackPromotion: fix a problem with promoted allocations in dead-end regions #67082

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Merged
merged 1 commit into from
Jul 3, 2023
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StackPromotion: fix a problem with promoted allocations in dead-end regions #67082

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20 changes: 7 additions & 13 deletions SwiftCompilerSources/Sources/Optimizer/FunctionPasses/StackPromotion.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -68,6 +68,11 @@ private func tryPromoteAlloc(_ allocRef: AllocRefInstBase,
return false
}

// The most important check: does the object escape the current function?
if allocRef.isEscaping(context) {
return false
}

if deadEndBlocks.isDeadEnd(allocRef.parentBlock) {

// Allocations inside a code region which ends up in a no-return block may missing their
Expand All @@ -77,11 +82,8 @@ private func tryPromoteAlloc(_ allocRef: AllocRefInstBase,
// ...
// unreachable // The end of %k's lifetime
//
// Also, such an allocation cannot escape the function, because the function does not
// return after the point of allocation. So we can stack-promote it unconditionally.
//
// There is one exception: if it's in a loop (within the dead-end region) we must not
// extend its lifetime. On the other hand we can be sure that its final release is not
// extend its lifetime. In this case we can be sure that its final release is not
// missing, because otherwise the object would be leaking. For example:
//
// bb1:
Expand All @@ -93,20 +95,12 @@ private func tryPromoteAlloc(_ allocRef: AllocRefInstBase,
//
// Therefore, if the allocation is inside a loop, we can treat it like allocations in
// non dead-end regions.
if !isInLoop(block: allocRef.parentBlock, context),
// TODO: for some reason this doesn't work for aysnc functions.
// Maybe a problem with co-routine splitting in LLVM?
!allocRef.parentFunction.isAsync {
if !isInLoop(block: allocRef.parentBlock, context) {
allocRef.setIsStackAllocatable(context)
return true
}
}

// The most important check: does the object escape the current function?
if allocRef.isEscaping(context) {
return false
}

// Try to find the top most dominator block which dominates all use points.
// * This block can be located "earlier" than the actual allocation block, in case the
// promoted object is stored into an "outer" object, e.g.
Expand Down