[all-commits] [llvm/llvm-project] c3b8bd: [InstCombine] Always try to invert non-canonical p...

[Roman Lebedev via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: c3b8bd1eea5b74b6cd4a89f3c221bc2dfa891248
      https://github.com/llvm/llvm-project/commit/c3b8bd1eea5b74b6cd4a89f3c221bc2dfa891248
  Author: Roman Lebedev <lebedev.ri at gmail.com>
  Date:   2020-07-04 (Sat, 04 Jul 2020)

  Changed paths:
    M llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
    M llvm/lib/Transforms/InstCombine/InstCombineInternal.h
    M llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
    M llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
    M llvm/test/ThinLTO/X86/cfi-devirt.ll
    M llvm/test/Transforms/InstCombine/canonicalize-selects-icmp-condition-bittest.ll
    M llvm/test/Transforms/InstCombine/icmp-mul-zext.ll
    M llvm/test/Transforms/InstCombine/logical-select.ll
    M llvm/test/Transforms/InstCombine/select-with-bitwise-ops.ll
    M llvm/test/Transforms/InstCombine/shift.ll
    M llvm/test/Transforms/LoopUnroll/runtime-loop-multiple-exits.ll
    M llvm/test/Transforms/PGOProfile/chr.ll
    M llvm/test/Transforms/SimplifyCFG/merge-cond-stores.ll

  Log Message:
  -----------
  [InstCombine] Always try to invert non-canonical predicate of an icmp

Summary:
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.

Reviewers: spatel, jdoerfert, nikic

Reviewed By: nikic

Subscribers: zzheng, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D83139