__attribute__ aligned could be more efficient

[Mason <slash dot tmp at free dot fr>]

Hello everyone,

Consider the following program.

#include <stdio.h>
#include <stddef.h>
struct foo1 { char s[80]; };
struct foo2 { char s[80]; }  __attribute__ ((aligned (64)));
struct bar1 { struct foo1 f; int i; };
struct bar2 { struct foo2 f; int i; };
#define P(arg) printf("sizeof(" #arg ") = %u\n", (unsigned)sizeof(arg))

int main(void)
{
  P(struct foo1);
  P(struct foo2);
  P(struct bar1); printf("offset=%u\n", (unsigned)offsetof(struct bar1, i));
  P(struct bar2); printf("offset=%u\n", (unsigned)offsetof(struct bar2, i));
  return 0;
}

$ gcc -O3 -Wall align.c 
$ ./a.out
sizeof(struct foo1) = 80
sizeof(struct foo2) = 128
sizeof(struct bar1) = 84
offset=80
sizeof(struct bar2) = 192
offset=128

I didn't expect sizeof(struct bar2) to be 192.

gcc lays out bar2 like this:
foo2(80) padding(48) i(4) padding(60)

But it seems (to me) that gcc could fit the "int" field in the
first padding, to save space:

foo2(80) i(4) padding(44)

Is there a way to "cancel" the alignment request for foo2
in the bar2 definition? This doesn't work:

struct bar3 {
  struct foo2 f __attribute__ ((aligned (4)));
  int i;
} __attribute__ ((aligned (64)));

Regards.