[PATCH] D87163: [DSE] Switch to MemorySSA-backed DSE by default.

[Florian Hahn via Phabricator via cfe-commits]

fhahn added a comment.

Note that we now also have to compute the PostDominatorTree, which adds an extra bit of compile-time overhead. By adjusting the pipeline a bit more, we can re-use ADCE's PDTs in most cases, which gives a `-0.18%` geomean improvement for -O3 D87322 <https://reviews.llvm.org/D87322> http://llvm-compile-time-tracker.com/compare.php?from=15fdd6cd7c24c745df1bb419e72ff66fd138aa7e&to=481f494515fc89cb7caea8d862e40f2c910dc994&stat=instructions

Ideally we would preserve the PDT, but my first try with using DomTreeUpdater introduced a significant compile-time regression, so I put that on hold for now.

I don't think it is worth holding off flipping the default for those changes. They can be done as follow-ups I think and there probably will also be a few other small issues to iron out. The compile-time numbers shared are without the recent improvements to MemDepAnalysis (which sped up legacy DSE a bit), so the temporary change will be slightly bigger.


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https://reviews.llvm.org/D87163