Steve Ellcey <steve.ell...@imgtec.com> writes: > Or one could change convert_mult_to_fma to add a check if fma is fused > vs. non-fused in addition to the check for the flag_fp_contract_mode > in order to decide whether to convert expressions into an fma and then > define fma instructions in the md file.
I was about to say that I see no reason to change how non-fused multiply adds work i.e. leave them to pattern matching but I think your point was that when both fused and non-fused patterns are available then what should we do. > I was wondering if anyone had an opinion about the advantages or > disadvantages of these two approaches. I expect that fused multiply adds are almost always faster in hardware owing to the lack of rounding so using them eagerly, when fp-contract allows, may still be best even if non-fused alternatives are available. That depends on the relative cost of the two alternatives though. Matthew
