[Bug target/107025] New: gas doesn't accept code produced by -mcpu=thunderx3t110

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107025

            Bug ID: 107025
           Summary: gas doesn't accept code produced by
                    -mcpu=thunderx3t110
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rsandifo at gcc dot gnu.org
                CC: ktkachov at gcc dot gnu.org, pinskia at gcc dot gnu.org,
                    rearnsha at gcc dot gnu.org
  Target Milestone: ---
            Target: aarch64*-*-*

Compiling:

void foo (_Atomic int *ptr) { ptr[1] = 1; }

with -O2 -mcpu=thunderx3t110 produces:

Error: selected processor does not support `stlur w1,[x0,4]'

This is because thunderx3t110 is listed as an Armv8.3-A core,
but includes the Armv8.4-A RCPC extension:

AARCH64_CORE("thunderx3t110",  thunderx3t110,  thunderx3t110, V8_3A, 
AARCH64_F\
L_CRYPTO | AARCH64_FL_RCPC | AARCH64_FL_SM4 | AARCH64_FL_SHA3 |
AARCH64_FL_F16F\
ML | AARCH64_FL_RCPC8_4, thunderx3t110, 0x43, 0x0b8, 0x0a)

This extension doesn't have its own separate feature flag in
gcc, gas, or clang.  I guess the options are to add one or
to remove the AARCH64_FL_RCPC8_4 entry.