search for: isfsqrtcheap

...on to this already. I always thought that's what -march was made for, really. GNOMETOYS On Sat, Nov 11, 2017 at 10:25 AM, Sanjay Patel via llvm-dev < llvm-dev at lists.llvm.org> wrote: > Yes - I was thinking of FeatureFastScalarFSQRT / FeatureFastVectorFSQRT > which are used by isFsqrtCheap(). These were added to override the default > x86 sqrt estimate codegen with: > https://reviews.llvm.org/D21379 > > But I'm not sure we really need that kind of hack. Can we adjust the > attribute in clang based on the target cpu? Ie, if you have something like: > $ clang -O2...

Are you referring to the X86TargetLowering::isFsqrtCheap hook? ~Craig On Fri, Nov 10, 2017 at 7:39 AM, Sanjay Patel <spatel at rotateright.com> wrote: > We can tie a user preference / override to a CPU model. We do something > like that for square root estimates already (although it does use a > SubtargetFeature currently for x86; ideal...

...hat's what > -march was made for, really. > > GNOMETOYS > > On Sat, Nov 11, 2017 at 10:25 AM, Sanjay Patel via llvm-dev < > llvm-dev at lists.llvm.org> wrote: > >> Yes - I was thinking of FeatureFastScalarFSQRT / FeatureFastVectorFSQRT >> which are used by isFsqrtCheap(). These were added to override the default >> x86 sqrt estimate codegen with: >> https://reviews.llvm.org/D21379 >> >> But I'm not sure we really need that kind of hack. Can we adjust the >> attribute in clang based on the target cpu? Ie, if you have something lik...

...Sat, Nov 11, 2017 at 10:25 AM, Sanjay Patel via llvm-dev >> <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote: >> >> Yes - I was thinking of FeatureFastScalarFSQRT / >> FeatureFastVectorFSQRT which are used by isFsqrtCheap(). >> These were added to override the default x86 sqrt >> estimate codegen with: >> https://reviews.llvm.org/D21379 >> >> But I'm not sure we really need that kind of hack. Can we >> adjust the attr...

...;>>> >>>> On Sat, Nov 11, 2017 at 10:25 AM, Sanjay Patel via llvm-dev < >>>> llvm-dev at lists.llvm.org> wrote: >>>> >>>>> Yes - I was thinking of FeatureFastScalarFSQRT / >>>>> FeatureFastVectorFSQRT which are used by isFsqrtCheap(). These were added >>>>> to override the default x86 sqrt estimate codegen with: >>>>> https://reviews.llvm.org/D21379 >>>>> >>>>> But I'm not sure we really need that kind of hack. Can we adjust the >>>>> attribute in...

I agree that a less x86 specific command line makes sense. I've been having an internal discussions with gcc folks and their evaluating switching to something like -mprefer-vector-width=128/256/512/none Based on the current performance data we're seeing, we think we need to ultimately default skylake-avx512 to -mprefer-vector-width=256. If we go with a target independent