[PATCH] D68408: [InstCombine] Unfold `sub %x, %y` -> `add (sub 0, %y), %x` IFF `%y` can be freely negated

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

> This *is* unusual. Is this too ugly to live?

I'd prefer to actually transform the operation tree at the point we decide it's profitable, to make it clear we can't end up in an infinite loop or something like that.  As it is, you're depending on some other transforms happening in a particular order, and it's not clear that will happen consistently.  (Yes, it's a little more code, but I think that's okay.)


Repository:
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  https://reviews.llvm.org/D68408/new/

https://reviews.llvm.org/D68408