[Bug regression/93009] New: AVX512 FMA - wrong code generation

[matthias.hochsteger at tuwien dot ac.at]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93009

            Bug ID: 93009
           Summary: AVX512 FMA - wrong code generation
           Product: gcc
           Version: 9.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: regression
          Assignee: unassigned at gcc dot gnu.org
          Reporter: matthias.hochsteger at tuwien dot ac.at
  Target Milestone: ---

Created attachment 47526
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=47526&action=edit
preprocessed code

Hello,

gcc 9.2 produces wrong output when compiling for AVX512 targets, depending on
the optimization level. The preprocessed source file is attached.

Correct output:
> g++ -std=c++17 -march=skylake-avx512 -O1 test_fma.ii
> g++ -std=c++17 -march=skylake-avx512 -O2 -fno-expensive-optimizations test_fma.ii
> 7.95851e-06

Wrong output:
> g++ -std=c++17 -march=skylake-avx512 -O1 -fexpensive-optimizations test_fma.ii
> g++ -std=c++17 -march=skylake-avx512 -O2 test_fma.ii
> 1e-10

All four cases work if the (non-preprocessed) source file is compiled with gcc
8.3, or the target is "skylake" instead of "skylake-avx512".

gcc -v

Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /build/gcc/src/gcc/configure --prefix=/usr --libdir=/usr/lib
--libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info
--with-bugurl=https://bugs.archlinux.org/
--enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++,d --enable-shared
--enable-threads=posix --with-system-zlib --with-isl --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-clocale=gnu --disable-libstdcxx-pch
--disable-libssp --enable-gnu-unique-object --enable-linker-build-id
--enable-lto --enable-plugin --enable-install-libiberty
--with-linker-hash-style=gnu --enable-gnu-indirect-function --enable-multilib
--disable-werror --enable-checking=release --enable-default-pie
--enable-default-ssp --enable-cet=auto gdc_include_dir=/usr/include/dlang/gdc
Thread model: posix
gcc version 9.2.0 (GCC) 

Best,
Matthias