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rscottmanley (Scott Manley)
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Nov 15 2018, 2:10 PM (97 w, 5 d)

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May 29 2020

rscottmanley added a comment to D80801: [DAGCombiner] allow more folding of fadd + fmul into fma.

Given the constraints in SDAG, we should choose the (fma(fma)) variant by default (assuming as we do here that the target has fma instructions). For example on x86, our best perf heuristic at this stage of compilation on any recent Intel or AMD core is number of uops. The option with separate fmul and fadd always has more uops, so it would be backwards to choose that sequence here and then try to undo that later.

May 29 2020, 2:46 PM · Restricted Project
rscottmanley added a comment to D80801: [DAGCombiner] allow more folding of fadd + fmul into fma.

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?

May 29 2020, 12:33 PM · Restricted Project
rscottmanley added a comment to D80801: [DAGCombiner] allow more folding of fadd + fmul into fma.

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?

May 29 2020, 10:24 AM · Restricted Project

Jul 30 2019

Herald added a project to D30247: Epilog loop vectorization: Restricted Project.
Jul 30 2019, 11:16 AM · Restricted Project