🚀 go-pugleaf

Hi,

I was looking at the code generated for the following program:

struct try {
        int     tr1;
        int     tr2;
        int     tr3;
        int     tr4;
};

int try1 (struct try *array, int *index)
{
        int     i;

        for (i = 0; i < 10; i++)
        {
                array[index[i]].tr3 = i;
                array[index[i]].tr2 = i + 10;
                array[index[i]].tr1 = i + 20;
        }
}


Most compilers assume that index and array could be aliased and reload index[i]
for each of the 3 indexes into array in the loop body.  So they load index[i]
and compute the address of array[index[i]] 3 times.  Is this really necessary
in ANSI C?  Can't we assume that index and array cannot overlap since they
point to non-compatible objects, and if you write to one you can screw up the
other?  Do any compilers assume that they are NOT aliased and optimize the
indexing?

Xlc has a -qansialias option but that doesn't seem to help.

Thanks,
Sanjoy