[Bug target/68543] New: Implement overflow arithmetic standard names {u,}{add,sub,mul}v4<mode> and/or negv3<mode>

[ktkachov at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68543

            Bug ID: 68543
           Summary: Implement overflow arithmetic standard names
                    {u,}{add,sub,mul}v4<mode> and/or negv3<mode>
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ktkachov at gcc dot gnu.org
  Target Milestone: ---

As mentioned in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66112#c13
we should consider implementing the various overflow arithmetic standard name
expanders that take a label argument and emit a jump to it if the operation
overflows.

A motivational example is the code quality regression from PR 68381:
int
foo(unsigned short x, unsigned short y)
{
  int r;
  if (__builtin_mul_overflow (x, y, &r))
    __builtin_abort ();
  return r;
}

which for aarch64 at -O3 generates:
foo:
        uxth    w0, w0
        uxth    w1, w1
        umull   x0, w0, w1
        tbnz    w0, #31, .L6
        mov     w2, 0
        cbnz    w2, .L6
        ret
.L6:
        stp     x29, x30, [sp, -16]!
        add     x29, sp, 0
        bl      abort

which could be improved