printf会影响到栈内存？有大佬能帮忙看看不，网上也查不到原因

#include <stdio.h>
int main(void)
{
int a=1;
int b=2;
int *ptr1;
ptr1=&a;
printf("ptr1:%d\n",*ptr1);
printf("ptr1_address:%p\n",ptr1);
--ptr1;
printf("ptr1:%d\n",*ptr1);
printf("ptr1_address:%p\n",ptr1);
printf("ptr1_address:%p\n",&b);
return 0;
}
这段代码用gcc编译后输出如下，看起来一切正常
ptr1:1
ptr1_address:0000003164fff6c4
ptr1:2
ptr1_address:0000003164fff6c0
ptr1_address:0000003164fff6c0
==================================================================
但是如果我把printf("ptr1_address:%p\n",&b);这一行注释掉，改成这样
#include <stdio.h>
int main(void)
{
int a=1;
int b=2;
int *ptr1;
ptr1=&a;
printf("ptr1:%d\n",*ptr1);
printf("ptr1_address:%p\n",ptr1);
--ptr1;
printf("ptr1:%d\n",*ptr1);
printf("ptr1_address:%p\n",ptr1);
//printf("ptr1_address:%p\n",&b);
return 0;
}
输出就会变成这样：
ptr1:1
ptr1_address:000000476edff90c
ptr1:35
ptr1_address:000000476edff908
================================================================
有大佬知道这里为什么ptr1--后不指向b了吗，或者说指向的指为啥出了问题呢