C/C++未定义行为

#include<iostream>

using namespace std;

 int main()
 {
    int j = 0;
    for (int i = 0; i < 10; i++)
    {
        j = (j++);
    }
    
    cout << j << endl;
     return 0;
 }

	.file	"test.cpp"
	.local	_ZStL8__ioinit
	.comm	_ZStL8__ioinit,1,1
	.text
	.globl	main
	.type	main, @function
main:
.LFB1021:
	.cfi_startproc
	pushq	%rbp
	.cfi_def_cfa_offset 16
	.cfi_offset 6, -16
	movq	%rsp, %rbp
	.cfi_def_cfa_register 6
	subq	$16, %rsp
	movl	$0, -8(%rbp)
	movl	$0, -4(%rbp)
.L3:
	cmpl	$9, -4(%rbp)
	jg	.L2
	movl	-8(%rbp), %eax
	leal	1(%rax), %edx
	movl	%edx, -8(%rbp)
	movl	%eax, -8(%rbp)
	addl	$1, -4(%rbp)
	jmp	.L3
.L2:
	movl	-8(%rbp), %eax
	movl	%eax, %esi
	movl	$_ZSt4cout, %edi
	call	_ZNSolsEi
	movl	$_ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_, %esi
	movq	%rax, %rdi
	call	_ZNSolsEPFRSoS_E
	movl	$0, %eax
	leave
	.cfi_def_cfa 7, 8
	ret
	.cfi_endproc
.LFE1021:
	.size	main, .-main
	.type	_Z41__static_initialization_and_destruction_0ii, @function
_Z41__static_initialization_and_destruction_0ii:
.LFB1027:
	.cfi_startproc
	pushq	%rbp
	.cfi_def_cfa_offset 16
	.cfi_offset 6, -16
	movq	%rsp, %rbp
	.cfi_def_cfa_register 6
	subq	$16, %rsp
	movl	%edi, -4(%rbp)
	movl	%esi, -8(%rbp)
	cmpl	$1, -4(%rbp)
	jne	.L7
	cmpl	$65535, -8(%rbp)
	jne	.L7
	movl	$_ZStL8__ioinit, %edi
	call	_ZNSt8ios_base4InitC1Ev
	movl	$__dso_handle, %edx
	movl	$_ZStL8__ioinit, %esi
	movl	$_ZNSt8ios_base4InitD1Ev, %edi
	call	__cxa_atexit
.L7:
	nop
	leave
	.cfi_def_cfa 7, 8
	ret
	.cfi_endproc
.LFE1027:
	.size	_Z41__static_initialization_and_destruction_0ii, .-_Z41__static_initialization_and_destruction_0ii
	.type	_GLOBAL__sub_I_main, @function
_GLOBAL__sub_I_main:
.LFB1028:
	.cfi_startproc
	pushq	%rbp
	.cfi_def_cfa_offset 16
	.cfi_offset 6, -16
	movq	%rsp, %rbp
	.cfi_def_cfa_register 6
	movl	$65535, %esi
	movl	$1, %edi
	call	_Z41__static_initialization_and_destruction_0ii
	popq	%rbp
	.cfi_def_cfa 7, 8
	ret
	.cfi_endproc
.LFE1028:
	.size	_GLOBAL__sub_I_main, .-_GLOBAL__sub_I_main
	.section	.init_array,"aw"
	.align 8
	.quad	_GLOBAL__sub_I_main
	.hidden	__dso_handle
	.ident	"GCC: (Ubuntu 5.4.0-6ubuntu1~16.04.12) 5.4.0 20160609"
	.section	.note.GNU-stack,"",@progbits

#include<iostream>

using namespace std;

int main()
{
003F18A1  mov         ebp,esp  
003F18A3  sub         esp,0D8h  
003F18A9  push        ebx  
003F18AA  push        esi  
003F18AB  push        edi  
003F18AC  lea         edi,[ebp-0D8h]  
003F18B2  mov         ecx,36h  
003F18B7  mov         eax,0CCCCCCCCh  
003F18BC  rep stos    dword ptr es:[edi]  
003F18BE  mov         ecx,offset _B1E6438A_源@cpp (03FC026h)  
003F18C3  ?? ?? 
003F18C4  ?? ?? 
003F18C5  ?? ?? 
003F18C6  ?? ?? 
003F18C7  ?? ?? 
003F18C8  ?? ?? 
003F18C9  ?? ?? 
003F18CA  ?? ?? 
003F18CB  ?? ?? 
    int j = 0;
003F18CC  add         byte ptr [eax],al  
003F18CE  ?? ?? 
003F18CF  ?? ?? 
003F18D0  ?? ?? 
003F18D1  ?? ?? 
003F18D2  ?? ?? 
    for (int i = 0; i < 10; i++)
003F18D3  add         byte ptr [eax],al  
003F18D5  add         bl,ch  
003F18D7  or          dword ptr [ebx-3F7C13BBh],ecx  
003F18DD  add         dword ptr [ecx+7D83EC45h],ecx  
003F18E3  in          al,dx  
    for (int i = 0; i < 10; i++)
003F18E4  or          bh,byte ptr [ebp+11h]  
    {
        j = (j++);
003F18E7  mov         eax,dword ptr [j]  
003F18EA  mov         dword ptr [j],eax  
003F18ED  mov         ecx,dword ptr [j]  
003F18F0  add         ecx,1  
003F18F3  mov         dword ptr [j],ecx  
    }
003F18F6  jmp         main+38h (03F18D8h)  

    cout << j << endl;
003F18F8  mov         esi,esp  
003F18FA  push        offset std::endl<char,std::char_traits<char> > (03F1253h)  
003F18FF  mov         edi,esp  
003F1901  mov         eax,dword ptr [j]  
003F1904  push        eax  
003F1905  mov         ecx,dword ptr [_imp_?cout@std@@3V?$basic_ostream@DU?$char_traits@D@std@@@1@A (03FB0A8h)]  
003F190B  call        dword ptr [__imp_std::basic_ostream<char,std::char_traits<char> >::operator<< (03FB09Ch)]  
003F1911  cmp         edi,esp  
003F1913  call        __RTC_CheckEsp (03F1230h)  
003F1918  mov         ecx,eax  
003F191A  call        dword ptr [__imp_std::basic_ostream<char,std::char_traits<char> >::operator<< (03FB0A0h)]  
003F1920  cmp         esi,esp  
003F1922  call        __RTC_CheckEsp (03F1230h)  
    return 0;
003F1927  xor         eax,eax  
}