[Bug target/118771] [15 regression] aarch64 bootstrap fails with --enabled-checking=release because of uninitialized warning

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118771

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |pinskia at gcc dot gnu.org
   Last reconfirmed|                            |2025-02-06
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |ASSIGNED

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
So looking into this. The problem is GCC does not realize that npieces is
non-zero (that is this is false positive but not enough information is provided
to GCC to figure it out).

I am deciding between adding:
```
gcc_assert (npieces > 0);
```
or
```
if (npieces <= 0)
  gcc_unreachable();
```

to aarch64_split_move .