[cfe-dev] [llvm-dev] RFC: change -fp-contract=off to actually disable FMAs

Matt Arsenault via cfe-dev cfe-dev at lists.llvm.org
Fri Jul 12 09:55:07 PDT 2019

> On Jul 12, 2019, at 12:32, Scott Manley <rscottmanley at gmail.com> wrote:
> I still have some confusion of what FMAD is supposed to be. Is FMAD actually MAD? Or is it something else? I am fine with leaving it alone if FMAD is not actually contracting floating point operations.

Yes. FMAD is supposed to give the same result as the separate FMUL and FADD with the intermediate rounding step. It exists because most of the combines for FMA still apply, and AMDGPU has an instruction that does this (as long as denormal flushing is OK). I don’t know of any other users.

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