[Bug target/114224] New: popcount RTL cost seems wrong with cssc

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114224

            Bug ID: 114224
           Summary: popcount RTL cost seems wrong with cssc
           Product: gcc
           Version: 14.0
            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

I noticed this with:
```
#include <stdint.h>
bool is_power_of_2_1(uint64_t value)
{
  return __builtin_popcountg(value) == 1;
}
```

Which I had expected to produce:
```
        cnt     x0, x0
        cmp     x0, 1
        cset    w0, eq
```

But instead we get:
```
        sub     x1, x0, #1
        eor     x0, x0, x1
        cmp     x0, x1
        cset    w0, hi
        ret
```