[Bug target/71806] New: PowerPC -mcpu=power9 enables __float128 without an explicit -mfloat128

[meissner at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71806

            Bug ID: 71806
           Summary: PowerPC -mcpu=power9 enables __float128 without an
                    explicit -mfloat128
           Product: gcc
           Version: 6.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: meissner at gcc dot gnu.org
  Target Milestone: ---

The macro ISA_3_0_MASKS_SERVER includes OPTION_MASK_FLOAT128_HW, which enables
the -mfloat128 option.  The -mfloat128 option being on by default means that
some of the libraries (libstdc++, libquadmath, etc.) will add code for IEEE
128-bit floating point.

Until all of the libraries are updated to support IEEE 128-bit, the
-mcpu=power9 support should not enable IEEE 128-bit floating point support
(either hardware or software).

In addition, if you configure the compiler with the --with-cpu=power9 option,
it should not enable IEEE 128-bit floating point support by default.

If the user uses -mcpu=power9 -mfloat128, it should enable the hardware support
that is available in ISA 3.0.