search for: mfma

Hi all, Recently I compiled the attached .c file using Clang with "-mavx2 -mfma -m32 -O3" optimization flags. First I used -emit-llvm and inspected the LLVM IR and there are no vector instructions. Then I got the assembly output of the file in it I can clearly see vector instructions in it. Neither the SLPVectorizer or the LoopVectorizer is however doing any vectorizati...

...9;t think the X86 backend will create any. > > ~Craig > > On Mon, Aug 21, 2017 at 8:49 AM, Charith Mendis via llvm-dev < > llvm-dev at lists.llvm.org> wrote: > >> >> Hi all, >> >> Recently I compiled the attached .c file using Clang with "-mavx2 -mfma >> -m32 -O3" optimization flags. >> >> First I used -emit-llvm and inspected the LLVM IR and there are no vector >> instructions. Then I got the assembly output of the file in it I can >> clearly see vector instructions in it. >> >> Neither the SLPVect...

...en might >> remember more of the gory details. >> >> Arguably, it is implicitly used when FMA formation is combined with >> fast-math, e.g.: >> >>     float foo(float x, float y) { >>       return x*(y + 1); >>     } >> >> Compiled with -mfma -ffast-math, this generates fma(x, y, x). Even >> though this transform superficially appears to use distributivity, >> that’s somewhat debatable because the fma computes the whole result >> without any intermediate rounding, so it’s pretty wishy-washy to say >> that it’...

Dear LLVM developers, I have a question on the fast-math floating-point optimizations applied by LLVM: Judging by the documentation at https://llvm.org/docs/LangRef.html#fast-math-flags I understood that rewriting with associativity and using reciprocal computations are possible optimizations. As the folklore description of fast-math is that it "applies real-valued identities", I

...gt;>>> Arguably, it is implicitly used when FMA formation is combined with >>>> fast-math, e.g.: >>>> >>>>     float foo(float x, float y) { >>>>       return x*(y + 1); >>>>     } >>>> >>>> Compiled with -mfma -ffast-math, this generates fma(x, y, x). Even >>>> though this transform superficially appears to use distributivity, >>>> that’s somewhat debatable because the fma computes the whole result >>>> without any intermediate rounding, so it’s pretty wishy-washy t...