[all-commits] [llvm/llvm-project] e9179a: [Support] improve known bits analysis for multiply...

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  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: e9179a6a029a501524cf3f34434c9dc2be4d74cc
      https://github.com/llvm/llvm-project/commit/e9179a6a029a501524cf3f34434c9dc2be4d74cc
  Author: Sanjay Patel <spatel at rotateright.com>
  Date:   2021-12-08 (Wed, 08 Dec 2021)

  Changed paths:
    M llvm/lib/Support/KnownBits.cpp
    M llvm/test/CodeGen/AMDGPU/sdiv64.ll
    M llvm/test/CodeGen/AMDGPU/srem64.ll
    M llvm/test/Transforms/InstCombine/icmp-mul.ll

  Log Message:
  -----------
  [Support] improve known bits analysis for multiply by power-of-2 (1 set bit)

This can be viewed as recognizing that multiply-by-power-of-2 doesn't
have a carry into the top bit of an M-bit * N-bit number.

Enhancing canonicalization of mul -> select might also handle some of
these if we were ok with increasing instruction count with casts in
some cases.

This doesn't help https://llvm.org/PR49055 , but it's a simpler
pattern that we miss.
Note: "-sccp" already gets these examples using a constant
range analysis.

Differential Revision: https://reviews.llvm.org/D114962