[OSSALifetimeCompletion] Handle unavailable blocks in dead-end regions. #68975
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OSSALifetimeCompletion needs to insert not at unreachable instructions that appear after the non-lifetime-ending boundary of a value but rather at the terminators of the availability boundary of the value within that region. Once it does so, it will no longer be sufficient to check whether the insertion point is an unreachable because such terminators may be another terminator that appears on the availability boundary. Prepare for that by recording the instructions that were found and checking whether the destroy insertion point is such an instruction before bailing rather than specifically checking for `unreachable`.
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atrick
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Oct 5, 2023
| @@ -1858,8 +1858,7 @@ right: | |||
| // CHECK: {{bb[^,]+}}([[INSTANCE:%[^,]+]] : @owned $C): | |||
| // CHECK: cond_br undef, [[BB1:bb[0-9]+]], [[BB4:bb[0-9]+]] | |||
| // CHECK: [[BB1]]: | |||
| // CHECK: [[COPY:%[^,]+]] = copy_value [[INSTANCE]] | |||
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I'm curious why this change eliminated a copy in mem2reg.
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This copy was incorrectly introduced in https://github.com/apple/swift/pull/68608/files#diff-8bd51ca385c836620fb33d8b5480d0ab38024c0ba38f83aa599f0a5148c48e7fR1861 . It was introduced because the unreachable instruction was added to liveness although the value is not available at it. This is fixed here by not adding unavailable terminators to liveness.
| @@ -409,6 +421,10 @@ class CanonicalizeOSSALifetime final { | |||
| void recordConsumingUser(SILInstruction *user) { | |||
| consumingBlocks.insert(user->getParent()); | |||
| } | |||
| void recordUnreachableLifetimeEnd(SILInstruction *user) { | |||
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At the definition of consumingBlocks and recordConsumingUser we should comment that these are either the points where the original value was consumed or was available at an unreachable instruction.
Not every block in a region which begins with the non-lifetime-ending boundary of a value and ending with unreachable-terminated blocks has the value available. If the unreachable-terminated blocks in this boundary are not available, it is incorrect to insert destroys of the value in them: it is an overconsume on some paths. Previously, however, destroys were simply being inserted at the unreachable. Here, this is fixed by finding the boundary of availability within that region and inserting destroys before the terminators of the blocks on that boundary. rdar://116255254
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@swift-ci please test |
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thank you! |
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Not every block in a region which begins with the non-lifetime-ending boundary of a value and ending with
unreachable-terminated blocks has the value available. If theunreachable-terminated blocks in this boundary are not available, it is incorrect to insert destroys of the value in them: it is an overconsume on some paths. Previously, however, destroys were simply being inserted at theunreachable.Here, this is fixed by finding the boundary of availability within that region and inserting destroys before the terminators of the blocks on that boundary.
rdar://116255254