What happens when compiling and decompiling programs?

#include <iostream>
using namespace std;
int main()
{
	cout<<"Hello World!"<<endl;
	return 0;
}

#include <iostream>
using namespace std;
int main()
{
	cout<<"Hello World!"<<endl;
	return 0;
}

# 1 "HelloWorld.cpp"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "HelloWorld.cpp"
# 1 "c:\\mingw\\lib\\gcc\\mingw32\\9.2.0\\include\\c++\\iostream" 1 3
# 36 "c:\\mingw\\lib\\gcc\\mingw32\\9.2.0\\include\\c++\\iostream" 3
       
# 37 "c:\\mingw\\lib\\gcc\\mingw32\\9.2.0\\include\\c++\\iostream" 3

# 1 "c:\\mingw\\lib\\gcc\\mingw32\\9.2.0\\include\\c++\\mingw32\\bits\\c++config.h" 1 3
# 252 "c:\\mingw\\lib\\gcc\\mingw32\\9.2.0\\include\\c++\\mingw32\\bits\\c++config.h" 3

# 252 "c:\\mingw\\lib\\gcc\\mingw32\\9.2.0\\include\\c++\\mingw32\\bits\\c++config.h" 3
namespace std
{
  typedef unsigned int size_t;
  typedef int ptrdiff_t;
  typedef decltype(nullptr) nullptr_t;
}

...

# 2 "HelloWorld.cpp" 2
# 2 "HelloWorld.cpp"
using namespace std;
int main()
{
 cout<<"Hello World!"<<endl;
 return 0;
}

	.file	"HelloWorld.cpp"
	.text
	.section .rdata,"dr"
__ZStL19piecewise_construct:
	.space 1
.lcomm __ZStL8__ioinit,1,1
	.def	___main;	.scl	2;	.type	32;	.endef
LC0:
	.ascii "Hello World!\0"
	.text
	.globl	_main
	.def	_main;	.scl	2;	.type	32;	.endef
_main:
LFB1515:
	.cfi_startproc
	leal	4(%esp), %ecx
	.cfi_def_cfa 1, 0
	andl	$-16, %esp
	pushl	-4(%ecx)
	pushl	%ebp
	.cfi_escape 0x10,0x5,0x2,0x75,0
	movl	%esp, %ebp
	pushl	%ecx
	.cfi_escape 0xf,0x3,0x75,0x7c,0x6
	subl	$20, %esp
	call	___main
	movl	$LC0, 4(%esp)
	movl	$__ZSt4cout, (%esp)
	call	__ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc
	movl	$__ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_, (%esp)
	movl	%eax, %ecx
	call	__ZNSolsEPFRSoS_E
	subl	$4, %esp
	movl	$0, %eax
	movl	-4(%ebp), %ecx
	.cfi_def_cfa 1, 0
	leave
	.cfi_restore 5
	leal	-4(%ecx), %esp
	.cfi_def_cfa 4, 4
	ret
	.cfi_endproc
LFE1515:
	.def	___tcf_0;	.scl	3;	.type	32;	.endef
___tcf_0:
LFB1993:
	.cfi_startproc
	pushl	%ebp
	.cfi_def_cfa_offset 8
	.cfi_offset 5, -8
	movl	%esp, %ebp
	.cfi_def_cfa_register 5
	subl	$8, %esp
	movl	$__ZStL8__ioinit, %ecx
	call	__ZNSt8ios_base4InitD1Ev
	leave
	.cfi_restore 5
	.cfi_def_cfa 4, 4
	ret
	.cfi_endproc
LFE1993:
	.def	__Z41__static_initialization_and_destruction_0ii;	.scl	3;	.type	32;	.endef
__Z41__static_initialization_and_destruction_0ii:
LFB1992:
	.cfi_startproc
	pushl	%ebp
	.cfi_def_cfa_offset 8
	.cfi_offset 5, -8
	movl	%esp, %ebp
	.cfi_def_cfa_register 5
	subl	$24, %esp
	cmpl	$1, 8(%ebp)
	jne	L6
	cmpl	$65535, 12(%ebp)
	jne	L6
	movl	$__ZStL8__ioinit, %ecx
	call	__ZNSt8ios_base4InitC1Ev
	movl	$___tcf_0, (%esp)
	call	_atexit
L6:
	nop
	leave
	.cfi_restore 5
	.cfi_def_cfa 4, 4
	ret
	.cfi_endproc
LFE1992:
	.def	__GLOBAL__sub_I_main;	.scl	3;	.type	32;	.endef
__GLOBAL__sub_I_main:
LFB1994:
	.cfi_startproc
	pushl	%ebp
	.cfi_def_cfa_offset 8
	.cfi_offset 5, -8
	movl	%esp, %ebp
	.cfi_def_cfa_register 5
	subl	$24, %esp
	movl	$65535, 4(%esp)
	movl	$1, (%esp)
	call	__Z41__static_initialization_and_destruction_0ii
	leave
	.cfi_restore 5
	.cfi_def_cfa 4, 4
	ret
	.cfi_endproc
LFE1994:
	.section	.ctors,"w"
	.align 4
	.long	__GLOBAL__sub_I_main
	.ident	"GCC: (MinGW.org GCC Build-20200227-1) 9.2.0"
	.def	__ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc;	.scl	2;	.type	32;	.endef
	.def	__ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_;	.scl	2;	.type	32;	.endef
	.def	__ZNSolsEPFRSoS_E;	.scl	2;	.type	32;	.endef
	.def	__ZNSt8ios_base4InitD1Ev;	.scl	2;	.type	32;	.endef
	.def	__ZNSt8ios_base4InitC1Ev;	.scl	2;	.type	32;	.endef
	.def	_atexit;	.scl	2;	.type	32;	.endef