[PATCH] D121323: [InstCombine] Fold select based logic of fcmps with same operands when FMF is present.

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.
craig.topper added reviewers: spatel, lebedev.ri, nikic, nlopes.
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If we have a logical and/or in select form and the true/false operand
is an fcmp with poison generating FMF, we won't be able to fold it
to an and/or instruction. This prevents us from optimizing the case
where it is a logical operation of two fcmps with identical operands.

This patch adds explicit checks for this case that doesn't rely on
converting to and/or to do the optimization. It reuses the existing
foldLogicOfFCmps, but adds a new flag to disable the other combine
that is inside that function.

FMF flags from the two FCmps are intersected using the logic added in
D121243 <https://reviews.llvm.org/D121243>. The FIXME has been updated to indicate that we can only use
a union for the non-select form.

This allows us to optimize cases like this from compare-fp-3.c in the
gcc torture suite with fast math.

void
test1 (float x, float y)
{

  if ((x==y) && (x!=y))
    link_error0();

}


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D121323

Files:
  llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
  llvm/lib/Transforms/InstCombine/InstCombineInternal.h
  llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
  llvm/test/Transforms/InstCombine/and-fcmp.ll
  llvm/test/Transforms/InstCombine/or-fcmp.ll

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