/* { dg-do compile } */
/* { dg-require-effective-target lp64 } */
/* { dg-options "-std=gnu99 -O2" } */
/* { dg-final { scan-assembler "salq\[ \\t\]+\\\$8, %rbx" } } */

#include <stdint.h>

register uint64_t global_flag_stack __asm__("rbx");

void push_flag_into_global_reg_var(uint64_t a, uint64_t b) {
  uint64_t flag = (a==b);
  global_flag_stack <<= 8;
  global_flag_stack  |= flag;
}