[PATCH] D83139: [InstCombine] Always try to invert non-canonical predicate of an icmp feeding select

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri created this revision.
lebedev.ri added reviewers: spatel, jdoerfert, nikic.
lebedev.ri added a project: LLVM.
Herald added a subscriber: hiraditya.

The actual transform i was going after was:
https://rise4fun.com/Alive/Tp9H

  Name: zz
  Pre: isPowerOf2(C0) && isPowerOf2(C1) && C1 == C0 
  %t0 = and i8 %x, C0
  %r = icmp eq i8 %t0, C1
    =>
  %t = icmp eq i8 %t0, 0
  %r = xor i1 %t, -1
  
  Name: zz
  Pre: isPowerOf2(C0) 
  %t0 = and i8 %x, C0
  %r = icmp ne i8 %t0, 0
    =>
  %t = icmp eq i8 %t0, 0
  %r = xor i1 %t, -1

but as it can be seen from the current tests, we already canonicalize most of it,
and we are only missing handling multi-use non-canonical icmp predicates.

If we have both `!=0` and `==0`, even though we can CSE them,
we end up being stuck with them. We should canonicalize to the `==0`.

I believe this is one of the cleanup steps i'll need after `-scalarizer`
if i end up proceeding with my WIP alloca promotion helper pass.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D83139

Files:
  llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
  llvm/test/Transforms/InstCombine/canonicalize-selects-icmp-condition-bittest.ll
  llvm/test/Transforms/InstCombine/select-with-bitwise-ops.ll

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