[all-commits] [llvm/llvm-project] 6c39a3: [InstCombine] fold not-shift of signbit to icmp+zext

[Sanjay Patel via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 6c39a3aae1dcce6ba1373289480c49c2d41e0a88
      https://github.com/llvm/llvm-project/commit/6c39a3aae1dcce6ba1373289480c49c2d41e0a88
  Author: Sanjay Patel <spatel at rotateright.com>
  Date:   2022-08-29 (Mon, 29 Aug 2022)

  Changed paths:
    M llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
    M llvm/test/Transforms/InstCombine/add.ll
    M llvm/test/Transforms/InstCombine/high-bit-signmask.ll

  Log Message:
  -----------
  [InstCombine] fold not-shift of signbit to icmp+zext

https://alive2.llvm.org/ce/z/j_8Wz9

The arithmetic shift was converted to logical shift with:
246078604c871d43

That does not seem to uncover any other missing/conflicting folds,
so convert directly to signbit test + cast.

We still need to fold the pattern with logical shift to test + cast.

This allows reducing patterns where the output type is not
the same as the input value:
https://alive2.llvm.org/ce/z/nydwFV

Fixes #57394