[all-commits] [llvm/llvm-project] 6a84af: [LAA] Use computeConstantDifference() (#103725)

[Nikita Popov via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 6a84af704f57defd919a4ec2e34b70a48d548719
      https://github.com/llvm/llvm-project/commit/6a84af704f57defd919a4ec2e34b70a48d548719
  Author: Nikita Popov <npopov at redhat.com>
  Date:   2024-08-16 (Fri, 16 Aug 2024)

  Changed paths:
    M llvm/lib/Analysis/LoopAccessAnalysis.cpp
    M llvm/lib/Analysis/ScalarEvolution.cpp

  Log Message:
  -----------
  [LAA] Use computeConstantDifference() (#103725)

Use computeConstantDifference() instead of casting getMinusSCEV() to
SCEVConstant. This can be much faster in some cases, because
computeConstantDifference() computes the result without creating new
SCEV expressions.

This improves LTO/ThinLTO compile-time for lencod by more than 10%.

I've verified that computeConstantDifference() does not produce worse
results than the previous code for anything in llvm-test-suite. This
required raising the iteration cutoff to 6. I ended up increasing it to
8 just to be on the safe side (for code outside llvm-test-suite), and
because this doesn't materially affect compile-time anyway (we'll almost
always bail out earlier).



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