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Don't pass dead values into proactively added phis in SILMem2Reg #36339

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Don't pass dead values into proactively added phis in SILMem2Reg #36339

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@meg-gupta meg-gupta commented Mar 6, 2021 •
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Mem2Reg proactively inserts phis. Some of the phis maybe operands to other phis but are not stored in any specific order in PhiBlocks structure. Instead of erasing phi's that are unnecessary, and walking up the phi operand chain to check if more phis need erasing, insert a end_lifetime at leaking blocks. Such phis will be cleaned up later by DCE.

Also until now, dead values (over consumed) maybe passed to such phis. This wasn't an issue in non-OSSA because there is no verification. In OSSA, this triggers a verifier assert. This PR fixes the OSSA SIL such that no over-consumed values are generated by Mem2Reg in such cases. It does this by identifying load [take] and destroy_addr to the alloc_stack within a block not followed by any store. Such blocks are marked in the deadValueBlock map which will be used while querying the live-out value to return undef.

Note this does not translate to a real bug.

Fixes rdar://79349413

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swift-ci commented Mar 6, 2021

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swift-ci commented Mar 6, 2021

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@meg-gupta meg-gupta marked this pull request as ready for review March 24, 2021 21:36
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Git Sha - 0075ef8cc1ed4dcf4fabee86c43824eea3547dfb

@meg-gupta meg-gupta changed the title Fixes for OSSA SILMem2Reg Cleanup dead phis in SILMem2Reg for OSSA May 18, 2021
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@meg-gupta meg-gupta force-pushed the mem2regnewfixes branch 2 times, most recently from c95fceb to fddba11 Compare May 18, 2021 21:36
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@meg-gupta meg-gupta changed the title Cleanup dead phis in SILMem2Reg for OSSA [WI]Cleanup dead phis in SILMem2Reg for OSSA May 18, 2021
@meg-gupta meg-gupta changed the title [WI]Cleanup dead phis in SILMem2Reg for OSSA [WIP] Cleanup dead phis in SILMem2Reg for OSSA May 18, 2021
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@meg-gupta meg-gupta force-pushed the mem2regnewfixes branch 2 times, most recently from 5b40be7 to d258c16 Compare May 20, 2021 17:58
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@meg-gupta meg-gupta changed the title [WIP] Cleanup dead phis in SILMem2Reg for OSSA Don't pass dead values into proactively added unnecessary phis in SILMem2Reg Jun 23, 2021
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@meg-gupta meg-gupta changed the title Don't pass dead values into proactively added unnecessary phis in SILMem2Reg Don't pass dead values into proactively added phis in SILMem2Reg Jun 25, 2021
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Opened #38265 as an alternate PR.

@meg-gupta meg-gupta closed this Jul 6, 2021
@meg-gupta meg-gupta mentioned this pull request Jul 6, 2021
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