[PATCH] D80801: [DAGCombiner] allow more folding of fadd + fmul into fma

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

In D80801#2063488 <https://reviews.llvm.org/D80801#2063488>, @rscottmanley wrote:

> Wouldn't it be better to choose between what you have here fmadd(a,b,fma(c,d,n)) and a*b + fmadd(c,d,n) for targets that perform worse with FMA chains?


Not sure if I'm understanding the question. Is there a target or a code pattern with a known disadvantage for the 2 fma variant?
Note that the entire set of transforms in visitFADDForFMACombine() is gated on legality checks for FMA(D) nodes, so we are assuming that these ops are supported if we reach this point in the code. There's also an existing target bailout with the generateFMAsInMachineCombiner() hook.


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