Hi Martin, I agree, we need more information from the compiler. Esp. whether the user specified `-mprefer-avx128` or `-mprefer-vector-width=none/128/256/512`. OTOH `-msve-vector-bits=N` is reported as __ARM_FEATURE_SVE_BITS. So that's covered.
Related: PR83875 - because while we're adding things in that area, it'd be nice if they worked with target clones as well. Are you aware of std::experimental::simd? It didn't make GCC 9.1, but you can easily patch your (installed) libstdc++ using https://github.com/VcDevel/ std-simd. Cheers, Matthias On Mittwoch, 22. Mai 2019 08:39:25 CEST Martin Reinecke wrote: > [Disclaimer: I sent this to gcc-help two weeks ago, but didn't get an > answer. Maybe the topic is more suited for the main gcc list ... I > really think the feature in question would be extremely useful to have, > and easy to add!] > > Hi, > > I'm currently writing an FFT library which tries to make use of SIMD > instructions and uses a lot of variables with > __attribute__ ((vector_size (xyz)) > > The resulting source is nicely portable and architecture-independent - > except for the one place where I need to determine the maximum > hardware-supported vector length on the target CPU. > > This currently looks like > > #if defined(__AVX__) > constexpr int veclen=32; > #elif defined(__SSE2__) > constexpr int veclen=16; > [...] > > This approach requires me to add an #ifdef for many architectures, most > of which I cannot really test on ... and new architectures will be > unsupported by default. > > Hence my question: is there a way in gcc to determine the hardware > vector length for the architecture the compiler is currently targeting? > Some predefined macro like > > HARDWARE_VECTOR_LENGTH_IN_BYTES > > which is 32 for AVX, 16 for SSE2, and has proper values for Neon, VPX > etc. etc. > > If this is not provided at the moment, would it bo possible to add this > in the future? This could massively simplify writing and maintaining > multi-platform SIMD code. > > Thanks, > Martin // -- ────────────────────────────────────────────────────────────────────────── Dr. Matthias Kretz https://kretzfamily.de GSI Helmholtzzentrum für Schwerionenforschung https://gsi.de SIMD easy and portable https://github.com/VcDevel/Vc ──────────────────────────────────────────────────────────────────────────
