[PATCH] D88687: [InstCombine] visitTrunc - pass through undefs for trunc(shift(trunc/ext(x),c)) patterns

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: lebedev.ri, nikic, spatel.
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Based on the recent patches D88475 <https://reviews.llvm.org/D88475> and D88429 <https://reviews.llvm.org/D88429> where we losing undef values due to extension/comparisons.

I've added a ConstantExpr::getUndefMask method that attempts to return a bool mask that is set to true for cases where the scalar/element was UndefValue - similar to Constant::replaceUndefsWith.

I've replaced the ConstantExpr::getUMin with a ConstantExpr::getUClamp method that can optionally pass through undefs, (else set it to the minimum value).

My hope is that I can next use ConstantExpr::getUndefMask to simplify D88420 <https://reviews.llvm.org/D88420>


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D88687

Files:
  llvm/include/llvm/IR/Constants.h
  llvm/lib/IR/Constants.cpp
  llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
  llvm/test/Transforms/InstCombine/cast.ll
  llvm/test/Transforms/InstCombine/trunc-shift-trunc.ll

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