[all-commits] [llvm/llvm-project] 6538b3: [NFC][InstCombine] Tests for "X - (X / C) * C == 0...

[Egor Bogatov via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 6538b3adbeee1c4cf2550014882fb36d3c8bf66d
      https://github.com/llvm/llvm-project/commit/6538b3adbeee1c4cf2550014882fb36d3c8bf66d
  Author: EgorBo <egorbo at gmail.com>
  Date:   2020-06-12 (Fri, 12 Jun 2020)

  Changed paths:
    A llvm/test/Transforms/InstCombine/add-shl-sdiv-to-srem.ll

  Log Message:
  -----------
  [NFC][InstCombine] Tests for "X - (X / C) * C == 0" pattern

See https://reviews.llvm.org/D79369


  Commit: 012909dcaf852d4260decd04a76dfe45e7d329c0
      https://github.com/llvm/llvm-project/commit/012909dcaf852d4260decd04a76dfe45e7d329c0
  Author: EgorBo <egorbo at gmail.com>
  Date:   2020-06-12 (Fri, 12 Jun 2020)

  Changed paths:
    M llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
    M llvm/test/Transforms/InstCombine/add-shl-sdiv-to-srem.ll

  Log Message:
  -----------
  [InstCombine] "X - (X / C) * C == 0" to "X & C-1 == 0"

Summary:
"X % C == 0" is optimized to "X & C-1 == 0" (where C is a power-of-two)
However, "X % Y" can also be represented as "X - (X / Y) * Y" so if I rewrite the initial expression:
"X - (X / C) * C == 0" it's not currently optimized to "X & C-1 == 0", see godbolt: https://godbolt.org/z/KzuXUj

This is my first contribution to LLVM so I hope I didn't mess things up

Reviewers: lebedev.ri, spatel

Reviewed By: lebedev.ri

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D79369


Compare: https://github.com/llvm/llvm-project/compare/425c6f079b9c...012909dcaf85