[PATCH] D120337: [InstCombine] Remove one-use limitation from X-Y==0 fold

[Nikita Popov via Phabricator via llvm-commits]

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This one-use limitation is artificial, we do not increase instruction count if we fold it with multiple uses. The motivating case is shown in `@sub_eq_zero_select`, where the one-use limitation causes us to miss a subsequent select fold.

I believe the backend is pretty good about reusing flag-producing subs for cmps with same operands, so I //think// doing this is fine.


https://reviews.llvm.org/D120337

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
  llvm/test/Transforms/InstCombine/icmp-sub.ll
  llvm/test/Transforms/InstCombine/prevent-cmp-merge.ll
  llvm/test/Transforms/InstCombine/result-of-usub-is-non-zero-and-no-overflow.ll

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