[Bug target/127832] New: (a&1)?-1:1 could be better

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127832

            Bug ID: 127832
           Summary: (a&1)?-1:1 could be better
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---
            Target: aarch64

Take:
```
signed  src(signed  x)
{
  return ((x&1)<<31)>>31 | 1;
}

signed  tgt(signed  x)
{
  return (x&1) ? -1 : 1;
}

signed  tgt1(signed  x)
{
  signed x1 = ~x;
  signed x2 = x1 & 1;
  return -1 + (x2<<1);
}
signed  tgt2(signed  x)
{
  signed x1 = x;
  signed x2 = x1 & 1;
  return 1 - (x2<<1);
}
```

These are all different ways to express `(x&1) ? -1 : 1`.  They all produce
different code.  

src produces the best code for aarch64.
While for riscv, src and tgt produce the same code and is the best.