[IRGen] Deadends don't need dealloc_pack_metadata. #73191
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There is a debug-build-only verification that is done for alloc_pack_metadata instructions that checks that there exist paired dealloc_pack_metadata instructions which will be keyed off of to clean up the on-stack variadic metadata packs corresponding to (the instruction after) the alloc_pack_metadata. StackNesting omits the deallocation instruction (as does PackMetadataMarkerInserter) if it would be created in a dead end block. If all blocks in the dominance frontier of the alloc_pack_metadata instruction are dead-end blocks, then the verification will incorrectly fail. It should not fail because it is not necessary to clean up the on-stack pack metadata (or any other stack allocations) in such a case. If all such blocks are dead-end blocks, however, the alloc_pack_metadata's block itself is a dead-end block as well. So during the verification, check whether the alloc_pack_metadata occurs in a dead-end block and do not fail verification if it does. rdar://125265980
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This was referenced Apr 24, 2024
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There is a debug-build-only verification that is done for alloc_pack_metadata instructions that checks that there exist paired dealloc_pack_metadata instructions which will be keyed off of to clean up the on-stack variadic metadata packs corresponding to (the instruction after) the alloc_pack_metadata.
StackNesting omits the deallocation instruction (as does PackMetadataMarkerInserter) if it would be created in a dead end block. If all blocks in the dominance frontier of the alloc_pack_metadata instruction are dead-end blocks, then the verification will incorrectly fail. It should not fail because it is not necessary to clean up the on-stack pack metadata (or any other stack allocations) in such a case.
If all such blocks are dead-end blocks, however, the alloc_pack_metadata's block itself is a dead-end block as well. So during the verification, check whether the alloc_pack_metadata occurs in a dead-end block and do not fail verification if it does.
rdar://125265980