[PATCH] D90527: [GlobalISel] ComputeKnownBits - minimum leading/trailing zero bits in shifts (PR44526)

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: arsenm, regehr, efriedma.
Herald added subscribers: kerbowa, hiraditya, rovka, nhaehnle, jvesely.
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Herald added a subscriber: wdng.

PR44526 - as detailed in https://blog.regehr.org/archives/1709 we don't make use of the known leading/trailing bits for shifted values in cases where we don't know the shift amount value.

This patch adds support to GISelKnownBits.computeKnownBitsImpl to use KnownBits::countMinTrailingZeros and countMinLeadingZeros to set the minimum guaranteed leading/trailing known zero/sign bits.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D90527

Files:
  llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
  llvm/test/CodeGen/AMDGPU/GlobalISel/lshr.ll

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