[all-commits] [llvm/llvm-project] 05670b: [InstCombine] Remove root special case in demanded...

[Nikita Popov via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 05670b42f5b45710bfdba48dcb7e8c30c8c7478f
      https://github.com/llvm/llvm-project/commit/05670b42f5b45710bfdba48dcb7e8c30c8c7478f
  Author: Nikita Popov <npopov at redhat.com>
  Date:   2024-07-02 (Tue, 02 Jul 2024)

  Changed paths:
    M clang/test/CodeGen/inline-asm-x86-flag-output.c
    M llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
    M llvm/test/Analysis/ValueTracking/phi-known-bits.ll
    M llvm/test/Transforms/InstCombine/assume-inseltpoison.ll
    M llvm/test/Transforms/InstCombine/assume.ll

  Log Message:
  -----------
  [InstCombine] Remove root special case in demanded bits simplification

When calling SimplifyDemandedBits (as opposed to
SimplifyDemandedInstructionBits), and there are multiple uses,
always use SimplifyMultipleUseDemandedBits and drop the special
case for root values.

This fixes the ephemeral value detection, as seen by the restored
assumes in tests. It may result in more or less simplification,
depending on whether we get more out of having demanded bits or
the ability to perform non-multi-use transforms. The change in
the phi-known-bits.ll test is because the icmp operand now gets
simplified based on demanded bits, which then prevents a different
known bits simplification later.

This also makes the code safe against future changes like
https://github.com/llvm/llvm-project/pull/97289, which add more
context that would have to be discarded for the multi-use case.



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