undefined behavior with realloc

realloc.c

#include <stdio.h>
#include <stdlib.h>

int main(void)
{
  int* p = (int *)malloc(sizeof(int));
  int* q = (int *)realloc(p, sizeof(int));
  *p = 1;
  *q = 2;
  if (p == q)
  {
    printf("%d %d\n", *p, *q);
  }
  return 0;
}

$ clang -O3 -Wall -S -emit-llvm foo.c; cat ./foo.ll
$ clang -O3 -S -mllvm --x86-asm-syntax=att foo.c; cat ./foo.s
$ clang -O3 -Wall foo.c ; ./a.out
1 2

https://stackoverflow.com/questions/26072752/realloc-dangling-pointers-and-undefined-behavior
https://stackoverflow.com/questions/40065322/realloc-lifetime-and-ub
http://www.open-std.org/jtc1/sc22/wg14/www/docs/summary.htm#dr_400
http://www.open-std.org/jtc1/sc22/wg14/www/docs/dr_260.htm
https://www.youtube.com/watch?v=g7entxbQOCc#t=25m56s
https://www.youtube.com/watch?v=v1COuU2vU_w