On Tue, Sep 6, 2011 at 5:30 PM, Bingfeng Mei <[email protected]> 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
>
>
