[PATCH] D61181: [WIP][DebugInfo] Avoid SelectionDAG un-necessarily debug-referring to dead VRegs

[Jeremy Morse via Phabricator via llvm-commits]

jmorse added a comment.

Sort-of ping at @bjope on this: this is fundamentally a speculative patch as I can't dig into the regressions being seen in D56151 <https://reviews.llvm.org/D56151>, and I have no expectations on other peoples time; however we'll need to think about whether those regressions block the placeDbgValues chain-of-things going into llvm-9, which will branch sometime soon (next month?). Similar to what I wrote in D56151 <https://reviews.llvm.org/D56151>, we have a choice of poisons for llvm-9:

- Leave placeDbgValues as it is,
- Disable placeDbgValues but don't commit D56151 <https://reviews.llvm.org/D56151>, which may cause dead variable locations to be resurrected during register coalescing,
- Disable placeDbgValues, commit D56151 <https://reviews.llvm.org/D56151>, triggering the regressions @bjope saw there, which may or may not be alleviated by this patch.

I'm fairly confident the issue in PR41583 (which I believe causes the seen regressions) can be addressed comprehensively, but likely not quickly. Delaying all these things doesn't bother me (fixing placeDbgValues has uncovered all kinds of other fun), but it should be a proactive decision.


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https://reviews.llvm.org/D61181