Fuxin Zhang writes:
> Hello,
> I've met a case where mipsel-linux-gcc -O2 fails,for both
> 2.96 and the fresh new 3.2.3. Maybe someone can tell me
> what's wrong.
Your code is incorrect.
> I've reduced the problem to the test case below,compile it
> with mipsel-linux-gcc -O2(FROM H.J.Lu's redhat miniport,all version,
> and 3.2.3 is tested too)
>
>
> #define PUT_CODE(x,code) ((x)->code = (code))
> union test_union {
> struct test *t;
> int a;
> };
>
> struct test {
> unsigned short code;
> union test_union u[1];
> };
>
> char memory[2000];
>
> struct test *test_alloc(int code)
> {
> struct test *t;
> int length=sizeof(struct test);
>
> t = (struct test*)memory;
> length = (sizeof(struct test) - sizeof(union test_union)-1)/sizeof(int);
> for (;length>=0;length--)
This is the errant line:
> ((int*)t)[length] = 0;
You have declared t as a pointer to struct test, but you're using it
as a pointer to int. If you look at Pointers, Section 6.2.2.3 in ISO
9899-1990 you'll see that this results in undefined behaviour.
-fno-strict-aliasing should generate the code you want, but it's
better to fix your source. If you want to use a pointer as a
different type, put it in a union.
Andrew.
