[PATCH] D126410: [InstCombine] fold icmp equality with udiv and large constant

[Sanjay Patel via Phabricator via llvm-commits]

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With large compare constant:
(X u/ Y) == C --> (X == C) && (Y == 1)
(X u/ Y) != C --> (X != C) || (Y != 1)

https://alive2.llvm.org/ce/z/EhKwh6

There are various potential missing icmp (div) transforms shown here:
https://github.com/llvm/llvm-project/issues/55695

This is a generalization for part of the udiv + equality. I didn't check in detail, but some of those may only make sense as codegen transforms.

This results in one extra instruction in IR, but it is better for analysis, and looks much better in codegen on all targets that I tried.


https://reviews.llvm.org/D126410

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
  llvm/test/Transforms/InstCombine/icmp-div-constant.ll

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