On Tue, Sep 6, 2011 at 5:30 PM, Bingfeng Mei <b...@broadcom.com> wrote:
> Hi,
> I compile the following code with arm gcc 4.6 (x86 is the similar with one of 
> 4.7 snapshot).
> I noticed "a" is written to memory three times instead of being added by 3 
> and written at the
> end. Doesn't restrict guarantee "a" won't be aliased to "p" so 3 "a++" can be 
> optimized?

No it does not.

> Thanks,
> Bingfeng Mei
>
> int a;
> int P[100];
> void foo (int * restrict p)
> {
>  P[0] = *p;
>  a++;
>  P[1] = *p;
>  a++;
>  P[2] = *p;
>  a++;
> }
>
> ~/work/install-arm/bin/arm-elf-gcc tst.c -O2 -S -std=c99
>
> foo:
>        @ args = 0, pretend = 0, frame = 0
>        @ frame_needed = 0, uses_anonymous_args = 0
>        @ link register save eliminated.
>        ldr     r3, .L2
>        ldr     r1, [r3, #0]
>        ldr     ip, [r0, #0]
>        ldr     r2, .L2+4
>        str     r4, [sp, #-4]!
>        add     r4, r1, #1
>        str     r4, [r3, #0]
>        str     ip, [r2, #0]
>        ldr     ip, [r0, #0]
>        add     r4, r1, #2
>        str     r4, [r3, #0]
>        str     ip, [r2, #4]
>        ldr     r0, [r0, #0]
>        add     r1, r1, #3
>        str     r0, [r2, #8]
>        str     r1, [r3, #0]
>        ldmfd   sp!, {r4}
>        bx      lr
>
>

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