[PATCH] D42739: [InstCombine] allow multi-use values in canEvaluate* if all uses are in 1 inst

[Sanjay Patel via Phabricator via llvm-commits]

spatel created this revision.
spatel added reviewers: aaboud, craig.topper.
Herald added a subscriber: mcrosier.

This is the enhancement suggested in https://reviews.llvm.org/D42536 to fix a shortcoming in regular InstCombine's canEvaluate* functionality.
When we have multiple uses of a value, but they're all in one instruction, we can allow that expression to be narrowed or widened for the same cost as a single-use value.

AFAICT, this can only matter for multiply: sub/and/or/xor/select would be simplified away if the operands are the same value; add becomes shl; shifts with a variable shift amount aren't handled.


https://reviews.llvm.org/D42739

Files:
  lib/Transforms/InstCombine/InstCombineCasts.cpp
  test/Transforms/InstCombine/cast-mul-select.ll
  test/Transforms/InstCombine/icmp-mul-zext.ll

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