[Bug middle-end/33970] Missed optimization using unsigned char loop variable

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33970

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |gjl at gcc dot gnu.org
         Resolution|                            |WORKSFORME
   Target Milestone|---                         |4.7.0
      Known to fail|                            |

--- Comment #13 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-07-20 
17:47:44 UTC ---
Cloased as WORKS FOR ME.

Using the following test case:


volatile unsigned char bar;

void foo(void)
{
    unsigned char x;
    for(x=0;x<128; x++)
    {
        bar = x;
    }
}

int sub2 (unsigned char);

void foo2 (void)
{
    unsigned char x;
    for(x=0;x<128; x++)
    {
        sub2 (x);
    }
}

void foo21 (void)
{
    unsigned char x;
    for(x=0;x<128; x++)
    {
        sub2 (x+1);
    }
}

And with avr-gcc 4.7 r176517 I get the following result (-Os -mmcu=atmega8).
In no case there is a 16-bit loop variable used.

foo:
    ldi r24,lo8(0)
.L5:
    sts bar,r24
    subi r24,lo8(-(1))
    cpi r24,lo8(-128)
    brne .L5
    ret

foo2:
    push r28
    ldi r28,lo8(0)
.L8:
    mov r24,r28
    rcall sub2
    subi r28,lo8(-(1))
    cpi r28,lo8(-128)
    brne .L8
    pop r28
    ret

foo21:
    push r28
    ldi r28,lo8(0)
.L11:
    subi r28,lo8(-(1))
    mov r24,r28
    rcall sub2
    cpi r28,lo8(-128)
    brne .L11
    pop r28
    ret

    .ident    "GCC: (GNU) 4.7.0 20110720 (experimental)"