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On Thu, 11 Jun 2015, Marek Polacek wrote:
+ (if (single_use (@2) && single_use (@3)) + (bit_xor @0 @1)))I don't think we should use single_use here. The result is never more complicated than the original. Sure, it might increase register pressure a bit in some cases, but we have not used that as a criterion for other simplifications in match.pd yet (LLVM does though).I don't have a strong preference here but we surely use single_use in match.pd elsewhere.
The criterion for single_use up to now has been whether we may end up with more operations after the transformation than before. Take:
(x & ~m) | (y & m) -> ((x ^ y) & m) ^ xIf (x & ~m) and (y & m) have other uses, we are going to compute them anyway, and the original is essentially a single bit_ior operation. After the transformation, we have 2 more operations. That's worse than we started with, so we don't do it.
-- Marc Glisse
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