[PATCH] D62266: [DAGCombine][X86][AArch64][ARM] (C - x) + y -> (y - x) + C fold

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

uaddo+subcarry doesn't really work the way you'd want it to on ARM... I think you have to invert the carry bit, and there isn't any convenient way to do that.  (Note the extra "SUB" between the ARMISD::ADDE and the ARMISD::SUBC.) So I think to get the optimal code here you have to produce neg+addcarry instead of subcarry.


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  rL LLVM

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  https://reviews.llvm.org/D62266/new/

https://reviews.llvm.org/D62266