[PATCH] D85593: [InstCombine] ~(~X + Y) -> X - Y

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

@spatel The category of "undef-unsafe" transforms is relatively narrow; it's specifically transforms that use identities that don't work with possibly-undef inputs.  For example, transforming x*2 -> x+x isn't legal because the bottom bit goes from zero to possibly-undef.  Some people have referred to it as "increasing the number of uses", but really it's "using algebraic rules that don't work with undef".  It doesn't have anything to do with the total number of uses of the value.


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https://reviews.llvm.org/D85593