search for: vfmadd231

Hi Kay, My patch will partially address your bug. For now I'm just looking to switch the default FMA from vfmadd213xx to vfmadd231xx. That will cause the code in PR17229 to compile as desired, but would regress code like: double foo(double a, double b, double c) { return a * b + c; } Which will now require a vmovaps + vfmadd231. If this impacts real benchmarks we could add an optimization to change the FMA variant based o...

...Kay Tiong Khoo > Cc: LLVM Developers Mailing List; Demikhovsky, Elena; Craig Topper > Subject: Re: [LLVMdev] Commutability of X86 FMA3 instructions. > > Hi Kay, > > My patch will partially address your bug. For now I'm just looking to switch the default FMA from vfmadd213xx to vfmadd231xx. That will cause the code in PR17229 to compile as desired, but would regress code like: > > double foo(double a, double b, double c) { > return a * b + c; > } > > Which will now require a vmovaps + vfmadd231. > > If this impacts real benchmarks we could add an optimizat...

Hi Lang, Unfortunately, I don't have an answer on the commutability question, but I wanted to let you know that I filed a bug on this: http://llvm.org/bugs/show_bug.cgi?id=17229 This also shows a memory operand variant of the fma that you may want to consider in your patch and testcases. Thanks! On Thu, Dec 19, 2013 at 10:45 PM, Lang Hames <lhames at gmail.com> wrote: > Hi all,

Hi all, The 213 variant of the FMA3 instructions is currently marked commutable (see X86InstrFMA.td). Is that safe? According to the ISA the FMA3 instructions aren't commutable for non-numeric results, so I'd have thought commuting this would only be valid in fast-math mode? For the curious, the reason that I'm asking is that we currently always select the 213 variant, but this