wat.c

#include <stdio.h>

typedef struct {} a;
typedef struct { a a1; a a2; } b;

int main(int argc, char * argv[])
{
  a as[999999];

  printf("%d\n", sizeof(b) == sizeof(a));
  printf("%zu\n", sizeof(as));

  int i;
  for(i = 0; i < sizeof(as) / sizeof(as[0]); i++)
  {
    puts("wat");
  }

  return 0;
}

/* $ gcc wat.c -O0 -o wat_
 * $ ./wat_ 
 * 1
 * 0
 * wat
 */

loop fragment:

{{{

0000000100000edd jmp 0x100000ef7
0000000100000edf leaq 0x0000007d(%rip),%rax
0000000100000ee6 movq %rax,%rdi
0000000100000ee9 callq 0x100000f24
0000000100000eee movl 0xdc(%rbp),%eax
0000000100000ef1 addl $0x01,%eax
0000000100000ef4 movl %eax,0xdc(%rbp)
0000000100000ef7 movl 0xdc(%rbp),%eax
0000000100000efa movslq %eax,%rax
0000000100000efd cmpq %rcx,%rax
0000000100000f00 jb 0x100000edf
}}}

sorry, forgot how to do github

0000000100000edd    jmp 0x100000ef7
0000000100000edf    leaq    0x0000007d(%rip),%rax
0000000100000ee6    movq    %rax,%rdi
0000000100000ee9    callq   0x100000f24
0000000100000eee    movl    0xdc(%rbp),%eax
0000000100000ef1    addl    $0x01,%eax
0000000100000ef4    movl    %eax,0xdc(%rbp)
0000000100000ef7    movl    0xdc(%rbp),%eax
0000000100000efa    movslq  %eax,%rax
0000000100000efd    cmpq    %rcx,%rax
0000000100000f00    jb  0x100000edf

0xdc(%rbp) is the loop counter, temporarily stashed in %rax / %eax
%ecx is the loop limit, set to zero at ..ebe
branch enters at ..ef7 and loop body at ..edf
cmpq at ..efd sets CF 0 and ZF 0, jb at ..f00 should NOT branch. does this particular compilation emit the "wat"?