[PATCH] D156401: [PatternMatch] Do not match constant expressions for binops

[Nikita Popov via Phabricator via llvm-commits]

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Currently, m_Mul style matchers also match constant expressions. This is a regular source of assertion failures (usually by trying to do a match and then cast to Instruction or BinaryOperator) and infinite combine loops. At the same time, I don't think this provides useful optimization capabilities (all of the tests affected here are regression tests for crashes / infinite loops).

Long term, all of these constant expressions (apart from add/sub possibly) are slated for removal per https://discourse.llvm.org/t/rfc-remove-most-constant-expressions/63179 -- but doing those removals can itself expose new crashed and infinite loops due to the current PatternMatch behavior. I've been working on removing and expressions, and I've already run into 3 issues of that kind.


https://reviews.llvm.org/D156401

Files:
  llvm/include/llvm/IR/PatternMatch.h
  llvm/test/Transforms/InstCombine/mul-inseltpoison.ll
  llvm/test/Transforms/InstCombine/mul.ll
  llvm/test/Transforms/InstCombine/pr32686.ll
  llvm/test/Transforms/InstCombine/switch-constant-expr.ll
  llvm/test/Transforms/InstCombine/udiv-simplify.ll

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