[PATCH] D155472: [DAG] Attempt shl narrowing in SimplifyDemandedBits

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon added inline comments.


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Comment at: llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp:1799
+          // which is equivalent to the narrow shift being NUW.
+          KnownBits Known0 = TLO.DAG.computeKnownBits(Op0, Depth + 1);
+          bool IsNUW = Known0.countMinLeadingZeros() >= (ShAmt + HalfWidth);
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nikic wrote:
> You shouldn't be directly calling computeKnownBits in SimplifyDemandedBits. Your new code needs to be moved after the SimplifyDemandedBits call below and use the Known it already computes for Op0.
I'll look into it - there are a number of cases where we don't do this though.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D155472/new/

https://reviews.llvm.org/D155472