[Bug driver/83206] -mfpu=auto does not work on ARM (armv7l-unknown-linux-gnueabihf)

[andrewm.roberts at sky dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83206

--- Comment #3 from Andrew Roberts <andrewm.roberts at sky dot com> ---
ok confirmed, this bug is still present on the gcc-7 branch, with the current
snapshot:

/usr/local/gcc-7.2.1/bin/gcc -v
Using built-in specs.
COLLECT_GCC=/usr/local/gcc-7.2.1/bin/gcc
COLLECT_LTO_WRAPPER=/usr/local/gcc-7.2.1/bin/../libexec/gcc/armv7l-unknown-linux-gnueabihf/7.2.1/lto-wrapper
Target: armv7l-unknown-linux-gnueabihf
Configured with: ../gcc-7.3.0/configure --prefix=/usr/local/gcc-7.3.0
--program-suffix= --disable-werror --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-gnu-unique-object
--enable-linker-build-id --with-linker-hash-style=gnu --enable-plugin
--enable-gnu-indirect-function --enable-lto --with-isl
--enable-languages=c,c++,fortran,lto --disable-libgcj --enable-clocale=gnu
--disable-libstdcxx-pch --enable-install-libiberty --disable-multilib
--disable-libssp --enable-default-pie --enable-default-ssp
--host=armv7l-unknown-linux-gnueabihf --build=armv7l-unknown-linux-gnueabihf
--with-arch=armv7-a --with-float=hard --with-fpu=vfpv3-d16 --disable-bootstrap
Thread model: posix
gcc version 7.2.1 20171123 (GCC)

/usr/local/gcc-7.2.1/bin/gcc -march=native -mcpu=cortex-a53  -mfpu=auto -Ofast
-o matrix matrix.c
cc1: error: -mfloat-abi=hard: selected processor lacks an FPU

Also the gcc man pages for 7.2.1 lack documentation for the -mfpu=auto option,
although it is accepted as an argument (gcc 8 does document it)

On 7.2.1 man page: 
      -mfpu=name
           This specifies what floating-point hardware (or hardware emulation)
           is available on the target.  Permissible names are: vfpv2, vfpv3,
           vfpv3-fp16, vfpv3-d16, vfpv3-d16-fp16, vfpv3xd, vfpv3xd-fp16,
           neon-vfpv3, neon-fp16, vfpv4, vfpv4-d16, fpv4-sp-d16, neon-vfpv4,
           fpv5-d16, fpv5-sp-d16, fp-armv8, neon-fp-armv8 and
           crypto-neon-fp-armv8.  Note that neon is an alias for neon-vfpv3
           and vfp is an alias for vfpv2.

On 8.0.0 man page:
       -mfpu=name
           This specifies what floating-point hardware (or hardware emulation)
           is available on the target.  Permissible names are: auto, vfpv2,
           vfpv3, vfpv3-fp16, vfpv3-d16, vfpv3-d16-fp16, vfpv3xd,
           vfpv3xd-fp16, neon-vfpv3, neon-fp16, vfpv4, vfpv4-d16, fpv4-sp-d16,
           neon-vfpv4, fpv5-d16, fpv5-sp-d16, fp-armv8, neon-fp-armv8 and
           crypto-neon-fp-armv8.  Note that neon is an alias for neon-vfpv3
           and vfp is an alias for vfpv2.