[Bug target/122525] New: uaddc5 and usubc5 optab is not implemented

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122525

            Bug ID: 122525
           Summary: uaddc5 and usubc5 optab is not implemented
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---
            Target: aarch64

Take:
```
struct h2
{
  unsigned long lo1;
  unsigned long  lo2;
  long hi;
};

struct h2 g2(struct h2 t0,  struct h2 t1)
{
  struct h2 t;
  unsigned long c;
  t.lo1 = __builtin_addcl(t0.lo1,  t1.lo1, 0, &c);
  t.lo2 = __builtin_addcl(t0.lo2,  t1.lo2, c, &c);
  t.hi = __builtin_addcl(t0.hi,  t1.hi, c, &c);
  return t;
}
```


This should just be:
```
        ldp     x9, x12, [x1]
        ldr     x13, [x1, #16]
        ldp     x10, x11, [x0]
        adds    x9, x10, x9
        ldr     x10, [x0, #16]
        adcs    x11, x11, x12
        stp     x9, x11, [x8]
        adc     x9, x13, x10
        str     x9, [x8, #16]
```

But current GCC produces:
```
        ldp     x4, x5, [x1]
        ldp     x3, x2, [x0]
        ldr     x0, [x0, 16]
        adds    x3, x3, x4
        cset    x4, cs
        adds    x2, x2, x5
        ldr     x5, [x1, 16]
        cset    x1, cs
        adds    x4, x4, x2
        stp     x3, x4, [x8]
        cset    x2, cs
        add     x0, x0, x5
        orr     x1, x1, x2
        add     x0, x0, x1
        str     x0, [x8, 16]
```


This is because the uaddc5 optab is not implemented for DImode.