[Bug middle-end/80902] New: A problem in expand_builtin_atomic_fetch_op

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80902

            Bug ID: 80902
           Summary: A problem in expand_builtin_atomic_fetch_op
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: segher at gcc dot gnu.org
  Target Milestone: ---

Since r247848 there are 633 FAILs in go and 131 FAILs in libgo, on
powerpc-linux.  What happens is the test for atomic.Xadd64 fails, in
runtime1.go, and then it throws an error but that itself crashes because
getg() returns 0, it hasn't been initialised yet.

The Xadd64 test fails because Xadd64 returns the original value, not the
modified value.  This is a problem in builtins.c; I have a patch.