[PATCH] D119369: [InstCombine] reduce mul operands based on undemanded high bits

[Sanjay Patel via Phabricator via llvm-commits]

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We already do this in SDAG, but mul was left out of the fold for unused high bits in IR.
The high bits of a mul's operands do not change the low bits of the result:
https://alive2.llvm.org/ce/z/XRj5Ek

Verify some test diffs to confirm that they are correct:
https://alive2.llvm.org/ce/z/y_W8DW
https://alive2.llvm.org/ce/z/7DM5uf
https://alive2.llvm.org/ce/z/GDiHCK

This gets a fold that was presumed not possible in D114272 <https://reviews.llvm.org/D114272>:
https://alive2.llvm.org/ce/z/tAN-WY

Removing nsw/nuw is needed for general correctness (and is also done in the codegen version), but we might be able to recover more of those with better analysis.


https://reviews.llvm.org/D119369

Files:
  llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
  llvm/test/Transforms/InstCombine/and-or.ll
  llvm/test/Transforms/InstCombine/icmp-mul-and.ll
  llvm/test/Transforms/InstCombine/mul-inseltpoison.ll
  llvm/test/Transforms/InstCombine/mul.ll

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