[Bug target/101471] New: AVX512 incorrect writemask generated for _mm512_fpclass_ps_mask in O0

["kastianoza at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101471

            Bug ID: 101471
           Summary: AVX512 incorrect writemask generated for
                    _mm512_fpclass_ps_mask in O0
           Product: gcc
           Version: 11.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kastianoza at gmail dot com
  Target Milestone: ---

It seems that in debug mode gcc generates an 8-bit write opmask, which causes
half of the result to be skipped when calling '_mm512_fpclass_ps_mask' (which
takes 16 floats and produces 16 bit result).
It doesn't happen in O1, when gcc generates instruction that doesn't take
writemask.


GCC info:
Using built-in specs.
COLLECT_GCC=g++-11
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/11/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
11.1.0-1ubuntu1~18.04.1' --with-bugurl=file:///usr/share/doc/gcc-11/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,m2 --prefix=/usr
--with-gcc-major-version-only --program-suffix=-11
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new
--enable-gnu-unique-object --disable-vtable-verify --enable-plugin
--enable-default-pie --with-system-zlib --enable-libphobos-checking=release
--with-target-system-zlib=auto --enable-objc-gc=auto --enable-multiarch
--disable-werror --disable-cet --with-arch-32=i686 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none=/build/gcc-11-YRKbe7/gcc-11-11.1.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-11-YRKbe7/gcc-11-11.1.0/debian/tmp-gcn/usr
--without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.1.0 (Ubuntu 11.1.0-1ubuntu1~18.04.1) 


Compilation command:
g++-11 fpclass_instruction.cpp -mavx512f -mavx512vl -mavx512bw -mavx512dq -ggdb
-O0

minimal example:

#include <immintrin.h>
#include <iostream>

int main() {
  __m512 x {
      1, 1, 1, 1,
      1, 1, 1, 1,
      0, 0, 0, 0,
      0, 0, 0, 0,  };
  auto ret = _mm512_fpclass_ps_mask(x, 0x26);
  std::cout << ret << std::endl;
}


relevant part of preprocessed code: (notice incorrect mask type : __mmask8)
# 7 "fpclass_instruction.cpp"
int main() {
  __m512 x {
      1, 1, 1, 1,
      1, 1, 1, 1,
      0, 0, 0, 0,
      0, 0, 0, 0, };
  auto ret = 
# 13 "fpclass_instruction.cpp" 3 4
            ((__mmask16) __builtin_ia32_fpclassps512_mask ((__v16sf) (__m512) (
# 13 "fpclass_instruction.cpp"
            x
# 13 "fpclass_instruction.cpp" 3 4
            ), (int) (
# 13 "fpclass_instruction.cpp"
            0x26
# 13 "fpclass_instruction.cpp" 3 4
            ),(__mmask8)-1))
# 13 "fpclass_instruction.cpp"
                                           ;
  std::cout << ret << std::endl;
}