pengfei added inline comments.
================ Comment at: clang/lib/Headers/avx512fintrin.h:9305 + * 1. The elements are reassociable when using fadd/fmul intrinsics; + * 2. There's no nan and signed zero in the elements when using fmin/max + intrinsics; ---------------- spatel wrote: > pengfei wrote: > > spatel wrote: > > > If I understand correctly, there's nothing preventing -0.0 or NaN values > > > in these ops. But if either of those are present, then the result is > > > potentially indeterminate. > > > > > > For the LLVM intrinsic, we have this text in LangRef: > > > "The result will always be a number unless all elements of the vector are > > > NaN. For a vector with minimum element magnitude 0.0 and containing both > > > +0.0 and -0.0 elements, the sign of the result is unspecified." > > Thanks @spatel for the information. I checked that the LLVM intrinsic does > > ignore the sign of zeros. https://godbolt.org/z/a9Yj8a. So we can remove > > the no signed zero assumption. > > But X86 fmin/fmax instructions have difference with the LLVM intrinsic, > > i.e. the result might be NaN even there's only one NaN in elements. > > Besides, the LangRef also says "If the intrinsic call has the nnan > > fast-math flag, then the operation can assume that NaNs are not present in > > the input vector." > > So we still need the no nan assumption here. > I understand the behavior that we want to specify for this API, but we are > not stating it clearly for the user. I think we should do that. How about: > > ``` > * For floating-point intrinsics: > * 1. When using fadd/fmul intrinsics, the order of operations within the > vector is unspecified (associative math). > * 2. When using fmin/fmax intrinsics, NaN or -0.0 elements within the vector > produce unspecified results. > ``` Great! It's much clear now. Thanks @spatel ! Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D93179/new/ https://reviews.llvm.org/D93179 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
