[PATCH] D26602: [DAGCombiner] do not fold (fmul (fadd X, 1), Y) -> (fmad X, Y, Y) by default

[Nicolai Hähnle via llvm-commits]

nhaehnle added a comment.

The optimization makes use of the distributive law, not the associative law. As such I don't think there should be an immediate connection to a flag named -fassociative-math. But maybe that just means that the flag is badly named :-)

Personally, I don't care about Clang flags since I'm worried about our OpenGL frontend which uses LLVM directly, but it seems to me that there are meaningful associativity transforms that can be done even when infs are possible. Are (a + b) + c --> a + (b + c) and (a * b) * c --> a * (b * c) problematic if any of the variables are inf or nan? I don't think so, but perhaps I'm missing something.


https://reviews.llvm.org/D26602