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

[gjl at gcc dot gnu.org]

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

Georg-Johann Lay <gjl at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|AVR-GCC                     |avr
           Priority|P3                          |P5
             Status|UNCONFIRMED                 |WAITING
   Last reconfirmed|                            |2015-02-20
     Ever confirmed|0                           |1

--- Comment #2 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
This cannot be reproduced with

register unsigned r4 asm ("r4");
extern unsigned x;

void f (void)
{
    r4 += x;
}


and compiled with

$ avr-gcc prog.c -S -Os


Neither with 4.8 nor 4.9 nor 5.0:  In all cases, the generated code is:

f:
    lds r24,x
    lds r25,x+1
    add r4,r24
    adc r5,r25
    ret


(In reply to NickParker from comment #0)

> c code:
> ---------------------------------------------------------
> register uint16_t phaseAccPh  asm ("r4");
> uint16_t phaseAccFr;
> 
> phaseAccPh += phaseAccFr;

This is not C code that can be compiled.  Please read the bug reporting
instructions again.

https://gcc.gnu.org/bugs/#report