[Bug tree-optimization/41244] New: "&data[i] - data" isn't converted to "i"

[zsojka at seznam dot cz]

In attached code:
in find(), generated code computes offset using multiplication/division.
in set(), generated code computes &data[10] and compares &data[i] with that (to
verify find() fails to be optimised because of overflow rules)

tested gcc: 4.3.4, 4.4.1, 4.5.0-alpha20090827

command line:
gcc main.c -o main.o -c -O3
-f(no-)strict-overflow or -m32 doesn't have any effect on that behaviour

---------------------------------
static struct {
        int a, b, c;
        char pad[200]; /* padding so offset computation has to use expensive
div/mul */
} data[1000]; /* 1000 so loop isn't unrolled */

int find(int val)
{
        int i;
        for (i = 0; i < 1000; i++) {
                if (data[i].a == val) return &data[i] - data; /* does *212,
/212 */
        }
        return -1;
}

void set(int val)
{
        int i;
        for (i = 0; i < 1000; i++) {
                data[i].b = &data[i] - data < 10 || data[i].a == val; /*
compares with &data[10] */
        }
}
---------------------------------

Relevant generated ASM:
(eax is "i", sar+imul is converted division by 212)
---------------------------------
        cdqe
        imul    rax, rax, 212
        sar     rax, 2
        imul    eax, eax, -1944890851
        ret
---------------------------------


-- 
           Summary: "&data[i] - data" isn't converted to "i"
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: zsojka at seznam dot cz
  GCC host triplet: x86_64-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41244