Hi Marcin, When using -march=skylake-avx512 by default it is using -mprefer-vector-width=256. You should use -mprefer-vector-width=512 explicitly to generate ZMMs. Sebastian > -----Original Message----- > > Hi, all! > > I compile the STREAM benchmark using gcc 8.1: > > gcc -march=skylake-avx512 -O3 -fopenmp stream.c -o stream > > The generated binary doesn't use ZMM registers (AVX512), only YMM registers > (AVX2). The same code compiled with GCC 7.2 looks as expected, i.e., 8-wide > vector instructions are used. > > Apparently Intel compiler doesn't generate ZMM instructions unless told so (- > qopt-zmm-usage=high). John McCalpin says the reason is the extra heating (and > the need to step down the frequency), e.g. > > https://software.intel.com/en-us/forums/intel-isa-extensions/topic/747994 > > > Does anyone know, if the same limitation is implemented in GCC 8? If so, is > there a flag to force GCC to generate AVX512 instructions? > > Thanks!
