[PATCH] D65150: [InstSimplify] Drop leftover "division-by-zero guard" around `@llvm.umul.with.overflow` overflow bit

[Nikita Popov via Phabricator via llvm-commits]

nikic added a comment.

I think this is something of a recurring pattern (not so much the and/or forms, but the original phi/select form), where we have `select (x != C1), y, C2`, where it turns out that `y[x = C1] == C2` and thus the whole expression reduces to `y` (same with phi's). We might want to invest in a general solution to this problem. Something along the lines of finding this kind of pattern, then checking `y` backwards for uses of `x` (to a small depth) and if we find them, replace `x` with `C1`, run InstSimplify over it and see if it reduces to `C2` in the end.


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