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.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D87163/new/

https://reviews.llvm.org/D87163

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