optimizing address calculation?

Hi, everyone.I encountered the problem and hope to get help from you.


Here is some structs definition.
typedef struct test{
int a[20];
int b[20];


}test1;


typedef struct test{
int c[20];
int d[20];
test1 test1a[20];
}test2;


test2 test2a;
test2 *pTest2a = &test2a;


in the program, I refer to the variable test2a by the pointer
for example


for(i = 0; i <20; i++)
{
        pTest2a->test1a[x].b[i] = i;
}


Although in the loop pTest2a->test1a[x] is fixed, it seems the
generated codes calculate
the address from pTest2a. If it is changed to the following:


int pInt = pTest2a->test1a[x].b;
for(i = 0; i < 20; i++)
{
        *pInt++ = i;
}
The new generated code is much faster.
Is it difficult for c compiler to generate the faster code?


Thanks
Jogging


[I don't think it's difficult, I think nested structures of arrays are
rare enough that the people who write optimizer in whatever compiler
you're using didn't worry about it. -John]

Return to the comp.compilers page.
Search the comp.compilers archives again.