[Bug target/79179] New: PowerPC64: -mcpu=power9 creates stxsd with bad offset

["anton at samba dot org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79179

            Bug ID: 79179
           Summary: PowerPC64: -mcpu=power9 creates stxsd with bad offset
           Product: gcc
           Version: 7.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: anton at samba dot org
                CC: meissner at gcc dot gnu.org, segher at gcc dot gnu.org,
                    wschmidt at gcc dot gnu.org
  Target Milestone: ---

The following test case:

#pragma pack(1)
struct {
        signed : 1;
        unsigned long a;
} b;

void c(void)
{
        b.a = 0;
        for (; b.a <= 45; b.a = (long)b.a + 1)
                ;
}

built with:

# gcc -O3 -mcpu=power9 crash1.i 

Creates an stxsd instruction with a bad offset:

/tmp/cckULtLs.s: Assembler messages:
/tmp/cckULtLs.s:32: Error: operand out of domain (1 is not a multiple of 4)

which is:

stxsd 12,1(9)