[PATCH] D117861: [SimplifyCFG] Enhance costmodel of FoldTwoEntryPHINode while consider branch misprediction

[Kai Luo via Phabricator via llvm-commits]

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This is the alternative method based on SimplifyCFG to solve problem mentioned in https://reviews.llvm.org/D113872, i.e., consider code

  loop:
  ...
  if (cond) {
    // update max/min values
    // update indexes of max/min values
  }

Currently simplifycfg transforms this snippet of code to

  loop:
    select cond ...
    select cond ...

This is not always profitable since we have redundant computations of select's operands. Branch is not always profitable either since branch may incur high mispredict penalty. This patch uses the cost estimation by @lebedev.ri mentioned in https://reviews.llvm.org/D113872.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D117861

Files:
  llvm/lib/Transforms/Utils/SimplifyCFG.cpp
  llvm/test/Transforms/SimplifyCFG/two-entry-phi-node-mispredict.ll

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