Problem of the Week 1, What's up with compilers?

memcpyIP.c

#include <string.h>
#include <stdio.h>
#include <stdint.h>

int main() {

        uint32_t ip;
        scanf("%u", &ip);

        uint8_t octets[4];
        memcpy(octets, &ip, sizeof(ip));

        printf("%u.%u.%u.%u\n", octets[3], octets[2], octets[1], octets[0]);
        return 0;
}
~    

memcpyIP.s

	.file	"memcpyIP.c"
	.section	.rodata.str1.1,"aMS",@progbits,1
.LC0:
	.string	"%u"
.LC1:
	.string	"%u.%u.%u.%u\n"
	.section	.text.unlikely,"ax",@progbits
.LCOLDB2:
	.section	.text.startup,"ax",@progbits
.LHOTB2:
	.p2align 4,,15
	.globl	main
	.type	main, @function
main:
.LFB47:
	.cfi_startproc
	subq	$24, %rsp
	.cfi_def_cfa_offset 32
	movl	$.LC0, %edi
	movq	%fs:40, %rax
	movq	%rax, 8(%rsp)
	xorl	%eax, %eax
	leaq	4(%rsp), %rsi
	call	__isoc99_scanf
	movl	4(%rsp), %eax
	movl	$1, %edi
	movl	%eax, %ecx
	movzbl	%ah, %esi
	movl	%eax, %edx
	shrl	$16, %ecx
	movl	%esi, %r8d
	shrl	$24, %edx
	movzbl	%al, %r9d
	movzbl	%cl, %ecx
	xorl	%eax, %eax
	movl	$.LC1, %esi
	call	__printf_chk
	movq	8(%rsp), %rdi
	xorq	%fs:40, %rdi
	jne	.L5
	xorl	%eax, %eax
	addq	$24, %rsp
	.cfi_remember_state
	.cfi_def_cfa_offset 8
	ret
.L5:
	.cfi_restore_state
	call	__stack_chk_fail
	.cfi_endproc
.LFE47:
	.size	main, .-main
	.section	.text.unlikely
.LCOLDE2:
	.section	.text.startup
.LHOTE2:
	.ident	"GCC: (Ubuntu 5.4.0-6ubuntu1~16.04.2) 5.4.0 20160609"
	.section	.note.GNU-stack,"",@progbits

unionIP.c

#include <stdio.h>
#include <stdint.h>

int main() {

        typedef union {
                uint32_t ipWord;
                unsigned char octets[4];
        } ip_t;

        ip_t ip;
        scanf("%u", &ip.ipWord);
        printf("%u.%u.%u.%u\n", ip.octets[3], ip.octets[2], ip.octets[1], ip.octets[0]);
        return 0;
}

unionIP.s

	.file	"unionIP.c"
	.section	.rodata.str1.1,"aMS",@progbits,1
.LC0:
	.string	"%u"
.LC1:
	.string	"%u.%u.%u.%u\n"
	.section	.text.unlikely,"ax",@progbits
.LCOLDB2:
	.section	.text.startup,"ax",@progbits
.LHOTB2:
	.p2align 4,,15
	.globl	main
	.type	main, @function
main:
.LFB23:
	.cfi_startproc
	subq	$24, %rsp
	.cfi_def_cfa_offset 32
	movl	$.LC0, %edi
	movq	%fs:40, %rax
	movq	%rax, 8(%rsp)
	xorl	%eax, %eax
	movq	%rsp, %rsi
	call	__isoc99_scanf
	movzbl	2(%rsp), %ecx
	movzbl	3(%rsp), %edx
	movl	$.LC1, %esi
	movzbl	(%rsp), %r9d
	movzbl	1(%rsp), %r8d
	xorl	%eax, %eax
	movl	$1, %edi
	call	__printf_chk
	movq	8(%rsp), %rsi
	xorq	%fs:40, %rsi
	jne	.L5
	xorl	%eax, %eax
	addq	$24, %rsp
	.cfi_remember_state
	.cfi_def_cfa_offset 8
	ret
.L5:
	.cfi_restore_state
	call	__stack_chk_fail
	.cfi_endproc
.LFE23:
	.size	main, .-main
	.section	.text.unlikely
.LCOLDE2:
	.section	.text.startup
.LHOTE2:
	.ident	"GCC: (Ubuntu 5.4.0-6ubuntu1~16.04.2) 5.4.0 20160609"
	.section	.note.GNU-stack,"",@progbits