[Bug target/100067] New: Unexpected warning for -mcpu=neoverse-n1 when configured with --with-fpu

["rearnsha at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100067

            Bug ID: 100067
           Summary: Unexpected warning for -mcpu=neoverse-n1 when
                    configured with --with-fpu
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rearnsha at gcc dot gnu.org
  Target Milestone: ---

If the compiler is configured with (for example):

--with-arch=armv7-a --with-fpu=neon --with-float=hard

then compiling with

gcc -S -mcpu=neoverse-n1 <any-c-file>

leads to an unexpected warning:
cc1: warning: switch ‘-mcpu=neoverse-n1’ conflicts with ‘-march=armv8.2-a’
switch

The same can be seen if -mfpu is passed explicitly on the command-line (which,
while it shouldn't happen, is slightly less surprising).

If -mfpu is specified to be anything other than auto (via command line or
configuration), it is expected that this will override *all* features from the
cpu/arch setting that relate to the use of the FPU.

Note, we should probably at this point progress the deprecation process for
-mfpu by deprecating the config option that allows this to be set during
configure.