[PATCH] D116483: [InstCombine] fold opposite shifts around an add

[Erik Desjardins via Phabricator via llvm-commits]

erikdesjardins created this revision.
Herald added a subscriber: hiraditya.
erikdesjardins requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

((X << C) + Y) >>u C --> (X + (Y >>u C)) & (-1 >>u C)

https://alive2.llvm.org/ce/z/DY9DPg

This replaces a shift with an 'and', and in the case
where the add has a constant operand, it eliminates
both shifts.

As noted in the TODO comment, we already have this fold when
the shifts are in the opposite order (and that code handles
bitwise logic ops too).

Fixes #52851


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D116483

Files:
  llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
  llvm/test/Transforms/InstCombine/lshr.ll
  llvm/test/Transforms/LoopVectorize/X86/gather_scatter.ll

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D116483.396880.patch
Type: text/x-patch
Size: 52168 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20220101/4dbb42b8/attachment-0001.bin>