[Bug middle-end/65082] Wasted cycles when using a register based varible

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65082

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |NEW

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reduced testcase:
```
typedef unsigned short uint16_t;


register uint16_t r4 asm ("r4");
register uint16_t r6 asm ("r6");

uint16_t pllExec(void)
{
  r4 += r6;
  return r4>>8;
};
```

We get:
        mov r24,r4
        mov r25,r5
        add r24,r6
        adc r25,r7
        mov r4,r24
        mov r5,r25
        mov r24,r25
        ldi r25,0