undefined action for c

test.c

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

int main(void) {
    int *p = malloc(sizeof(int));
    int *q = realloc(p, sizeof(int));
    int *z = realloc(q, sizeof(int));
    *p = 1;
    *q = 2;
    *z = 3;
    if (p == q)
        printf("%p %p %p %d %d %d\n", p, q, z, *p, *q, *z);
    return 0;
}

Code Title: Trinity

x64 osx result

$ clang -O test.c
$ ./a.out
0x7fbcf2404b50 0x7fbcf2404b50 0x7fbcf2404b50 1 2 3

$ gcc -o g.out test.c -O0
$ ./g.out
0x7fc4bac04b50 0x7fc4bac04b50 0x7fc4bac04b50 3 3 3

$ gcc -o g.out test.c -O2
11:27 $ ./g.out
0x7f9d3bc04b50 0x7f9d3bc04b50 0x7f9d3bc04b50 1 2 3

gcc -O2 result binary code

a.out:
(__TEXT,__text) section
_main:
0000000100000ec0    pushq   %rbp
0000000100000ec1    movq    %rsp, %rbp
0000000100000ec4    pushq   %r14
0000000100000ec6    pushq   %rbx
0000000100000ec7    subq    $0x10, %rsp
0000000100000ecb    movl    $0x4, %edi
0000000100000ed0    callq   0x100000f42             ## symbol stub for: _malloc
0000000100000ed5    movq    %rax, %r14
0000000100000ed8    movl    $0x4, %esi
0000000100000edd    movq    %r14, %rdi
0000000100000ee0    callq   0x100000f4e             ## symbol stub for: _realloc
0000000100000ee5    movq    %rax, %rbx
0000000100000ee8    movl    $0x4, %esi
0000000100000eed    movq    %rbx, %rdi
0000000100000ef0    callq   0x100000f4e             ## symbol stub for: _realloc
0000000100000ef5    movq    %rax, %rcx
0000000100000ef8    movl    $0x1, (%r14)
0000000100000eff    movl    $0x2, (%rbx)
0000000100000f05    movl    $0x3, (%rcx)
0000000100000f0b    cmpq    %rbx, %r14
0000000100000f0e    jne 0x100000f37
0000000100000f10    movl    $0x3, (%rsp)
0000000100000f17    leaq    0x64(%rip), %rdi        ## literal pool for: "%p %p %p %d %d %d\n"
0000000100000f1e    movl    $0x1, %r8d
0000000100000f24    movl    $0x2, %r9d
0000000100000f2a    xorl    %eax, %eax
0000000100000f2c    movq    %r14, %rdx
0000000100000f2f    movq    %r14, %rsi
0000000100000f32    callq   0x100000f48             ## symbol stub for: _printf
0000000100000f37    xorl    %eax, %eax
0000000100000f39    addq    $0x10, %rsp
0000000100000f3d    popq    %rbx
0000000100000f3e    popq    %r14
0000000100000f40    popq    %rbp
0000000100000f41    retq

gcc -O1 result binary code

o1.out:
(__TEXT,__text) section
_main:
0000000100000ec0    pushq   %rbp
0000000100000ec1    movq    %rsp, %rbp
0000000100000ec4    pushq   %r14
0000000100000ec6    pushq   %rbx
0000000100000ec7    subq    $0x10, %rsp
0000000100000ecb    movl    $0x4, %edi
0000000100000ed0    callq   0x100000f3c             ## symbol stub for: _malloc
0000000100000ed5    movq    %rax, %r14
0000000100000ed8    movl    $0x4, %esi
0000000100000edd    movq    %r14, %rdi
0000000100000ee0    callq   0x100000f48             ## symbol stub for: _realloc
0000000100000ee5    movq    %rax, %rbx
0000000100000ee8    movl    $0x4, %esi
0000000100000eed    movq    %rbx, %rdi
0000000100000ef0    callq   0x100000f48             ## symbol stub for: _realloc
0000000100000ef5    movq    %rax, %rcx
0000000100000ef8    movl    $0x1, (%r14)
0000000100000eff    movl    $0x2, (%rbx)
0000000100000f05    movl    $0x3, (%rcx)
0000000100000f0b    cmpq    %rbx, %r14
0000000100000f0e    jne 0x100000f31
0000000100000f10    movl    (%r14), %r8d
0000000100000f13    movl    (%rbx), %r9d
0000000100000f16    movl    $0x3, (%rsp)
0000000100000f1d    leaq    0x5a(%rip), %rdi        ## literal pool for: "%p %p %p %d %d %d\n"
0000000100000f24    xorl    %eax, %eax
0000000100000f26    movq    %rbx, %rdx
0000000100000f29    movq    %r14, %rsi
0000000100000f2c    callq   0x100000f42             ## symbol stub for: _printf
0000000100000f31    xorl    %eax, %eax
0000000100000f33    addq    $0x10, %rsp
0000000100000f37    popq    %rbx
0000000100000f38    popq    %r14
0000000100000f3a    popq    %rbp
0000000100000f3b    retq