[PATCH] D89317: [InstructionSimplify] icmp simplification

[Sjoerd Meijer via Phabricator via llvm-commits]

SjoerdMeijer created this revision.
SjoerdMeijer added reviewers: spatel, jdoerfert, lebedev.ri, dmgreen, craig.topper.
Herald added subscribers: pengfei, javed.absar, hiraditya.
Herald added a project: LLVM.
SjoerdMeijer requested review of this revision.

This improves simplifications for pattern `icmp (X+Y), (X+Z) -> icmp Y,Z` if only one of the operands has NSW set, e.g.:

  icmp slt (x + 5), (x +nsw 6)

We can still safely rewrite this to:

  icmp slt 5, 6

because we know that the LHS can't overflow if the RHS has NSW set and constant `Y <= Z`.

This is useful because ScalarEvolutionExpander which is used to generate code for SCEVs in different loop optimisers is not always able to put back NSW flags across control-flow.


https://reviews.llvm.org/D89317

Files:
  llvm/lib/Analysis/InstructionSimplify.cpp
  llvm/test/Transforms/InstSimplify/compare.ll

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