[PATCH] D114962: [Support] improve known bits analysis for multiply with 1-bit op (bool)

[Sanjay Patel via Phabricator via llvm-commits]

spatel created this revision.
spatel added reviewers: lebedev.ri, RKSimon, craig.topper.
Herald added subscribers: dexonsmith, hiraditya, mcrosier.
spatel requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

This can be viewed as recognizing that multiply-by-1 doesn't have any carry bits.

Enhancing canonicalization of mul -> select would also handle these if we were ok with increasing instruction count with casts in some cases.

This doesn't help https://llvm.org/PR49055 , but it's a simpler pattern that we miss.
Note: "-sccp" already gets these examples using a constant range analysis.


https://reviews.llvm.org/D114962

Files:
  llvm/lib/Support/KnownBits.cpp
  llvm/test/Transforms/InstCombine/icmp-mul.ll

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