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


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

--- Comment #18 from Andrew Roberts <andrewm.roberts at sky dot com> ---
Richard, I'm giving the latest snapshot a test, the armv6 version  will be
ready in 16 hrs or so...

Meanwhile a question about consistency with gcc -Q --help=target,
and also what happens if you don't specify -mcpu= with =mfpu=auto
tested with gcc version 8.0.0 20171210 (experimental) (GCC)

/usr/local/gcc/bin/gcc  -Q --help=target | grep "mcpu\|mfpu\|march"
  -march=                               armv7-a+fp
  -mcpu=
  -mfpu=                                vfpv3-d16

/usr/local/gcc/bin/gcc -march=native -Q --help=target | grep
"mcpu\|mfpu\|march"
  -march=                               armv7ve+vfpv3-d16
  -mcpu=
  -mfpu=                                vfpv3-d16

/usr/local/gcc/bin/gcc -march=native -mcpu=native -Q --help=target | grep
"mcpu\|mfpu\|march"
  -march=                               armv7ve+vfpv3-d16
  -mcpu=                                cortex-a7
  -mfpu=                                vfpv3-d16

/usr/local/gcc/bin/gcc -march=native -mcpu=native -mfpu=auto -Q --help=target |
grep "mcpu\|mfpu\|march"
  -march=                               armv7ve
  -mcpu=                                cortex-a7
  -mfpu=                                auto

So without anything specified generic arch is given and also a fpu.
-march=native fills in the arch with the correct one
whereas -mfpu=auto just says auto rather than what was selected

march=native gives different results depending on if -mfpu=auto is set

How does mfpu=auto impact cross compuilers? Will it just not be available? What
will happen in the future when its the default?

This was all on the Big/Little ODROID XU4, so it should really have been:
  -mcpu=                                cortex-a15.cortex-a7
When the patches for that issue land.

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