[PATCH] D124711: [DAGCombiner] When matching a disguised rotate by constant don't forget to apply LHSMask/RHSMask.

[Craig Topper via Phabricator via llvm-commits]

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We try to match as a disguised rotate by constant of these forms
(shl (X | Y), C1 <https://reviews.llvm.org/C1>) | (srl X, C2) --> (rotl X, C1 <https://reviews.llvm.org/C1>) | (shl Y, C1 <https://reviews.llvm.org/C1>)
(shl X, C1 <https://reviews.llvm.org/C1>) | (srl (X | Y), C2) --> (rotl X, C1 <https://reviews.llvm.org/C1>) | (srl Y, C2)

We may have also looked through an AND to find the shift. If we
did, we need to apply a mask to the result.

I'll add an AArch64 test and pre-commit it and the RISC-V test
tomorrow.

Fixes PR55201.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D124711

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/test/CodeGen/RISCV/pr55201.ll

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