[PATCH] D49229: [InstCombine] Fold redundant masking operations of shifted value

[Diogo N. Sampaio via Phabricator via llvm-commits]

dnsampaio created this revision.
dnsampaio added reviewers: spatel, samparker, efriedma.
Herald added a subscriber: llvm-commits.

Allow to reduce redundant shift masks, at the IR level.
For example:
x1 = x & 0xAB00
x2 = (x >> 8) & 0xAB

The x2 operation can be seen as
x2 = (x >> 8) & (0xAB00 >> 8)

>
-

x2 = (x & 0xAB00) >> 8

And finally reduced to
x2 = x1 >> 8

It only allows folding when the masks and shift values are constants.


Repository:
  rL LLVM

https://reviews.llvm.org/D49229

Files:
  lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
  lib/Transforms/InstCombine/InstCombineInternal.h
  test/Transforms/InstCombine/D48278.ll

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