[PATCH] D90479: [WIP][ValueTracking] ComputeKnownBits - minimum leading/trailing zero bits in LSHR/SHL (PR44526)

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: spatel, regehr, efriedma, lebedev.ri.
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RKSimon requested review of this revision.

Followup to D72573 <https://reviews.llvm.org/D72573> - as detailed in https://blog.regehr.org/archives/1709 we don't make use of the known leading/trailing zeros for shifted values in cases where we don't know the shift amount value.

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

This patch is a WIP - and is initially just a way to track the changes necessary to some existing tests.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D90479

Files:
  llvm/lib/Analysis/ValueTracking.cpp
  llvm/test/Transforms/InstCombine/and2.ll
  llvm/test/Transforms/InstCombine/lshr-and-negC-icmpeq-zero.ll
  llvm/test/Transforms/InstCombine/signbit-shl-and-icmpeq-zero.ll
  llvm/test/Transforms/InstCombine/zext-or-icmp.ll

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