User:Kim Bruning/Compiler metaprogramming example

From Wikipedia, the free encyclopedia

Here is an example of how one can use a compiler to generate large amounts of assembly code. It has been linked from metaprogramming because of the length of the example.

The following programme to count from 1 to 1000 is written in C++:

/* hello.cpp */
#include <iostream>

using std::cout;
using std::endl;

main() {
        for(int i=1 ; i <= 1000 ; i++) {
                std::cout << i << std::endl;
        }
}

Using the GNU GCC C++ compiler g++ to generate intel x86 assembler as follows:

 g++ hello.cpp -S

creates a new 221 line file hello.s as a result. The contents of this file is:

	.file	"hello.cpp"
	.local	_ZSt8__ioinit
	.comm	_ZSt8__ioinit,1,1
	.text
	.align 2
.globl main
	.type	main,@function
main:
.LFB1448:
	pushl	%ebp
.LCFI0:
	movl	%esp, %ebp
.LCFI1:
	subl	$24, %esp
.LCFI2:
	andl	$-16, %esp
	movl	$0, %eax
	subl	%eax, %esp
	movl	$1, -4(%ebp)
.L2:
	cmpl	$1000, -4(%ebp)
	jle	.L5
	jmp	.L3
.L5:
	movl	-4(%ebp), %eax
	movl	%eax, 4(%esp)
	movl	$_ZSt4cout, (%esp)
	call	_ZNSolsEi
	movl	$_ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_, 4(%esp)
	movl	%eax, (%esp)
	call	_ZNSolsEPFRSoS_E
	leal	-4(%ebp), %eax
	incl	(%eax)
	jmp	.L2
.L3:
	movl	$0, %eax
	leave
	ret
.LFE1448:
.Lfe1:
	.size	main,.Lfe1-main
	.align 2
	.type	_Z41__static_initialization_and_destruction_0ii,@function
_Z41__static_initialization_and_destruction_0ii:
.LFB1460:
	pushl	%ebp
.LCFI3:
	movl	%esp, %ebp
.LCFI4:
	subl	$24, %esp
.LCFI5:
	cmpl	$65535, 12(%ebp)
	jne	.L6
	cmpl	$1, 8(%ebp)
	jne	.L6
	movl	$_ZSt8__ioinit, (%esp)
	call	_ZNSt8ios_base4InitC1Ev
	movl	$__dso_handle, 8(%esp)
	movl	$0, 4(%esp)
	movl	$__tcf_0, (%esp)
	call	__cxa_atexit
.L6:
	leave
	ret
.LFE1460:
.Lfe2:
	.size	_Z41__static_initialization_and_destruction_0ii,.Lfe2-_Z41__static_initialization_and_destruction_0ii
	.align 2
	.type	__tcf_0,@function
__tcf_0:
.LFB1461:
	pushl	%ebp
.LCFI6:
	movl	%esp, %ebp
.LCFI7:
	subl	$8, %esp
.LCFI8:
	movl	$_ZSt8__ioinit, (%esp)
	call	_ZNSt8ios_base4InitD1Ev
	leave
	ret
.LFE1461:
.Lfe3:
	.size	__tcf_0,.Lfe3-__tcf_0
	.align 2
	.type	_GLOBAL__I_main,@function
_GLOBAL__I_main:
.LFB1463:
	pushl	%ebp
.LCFI9:
	movl	%esp, %ebp
.LCFI10:
	subl	$8, %esp
.LCFI11:
	movl	$65535, 4(%esp)
	movl	$1, (%esp)
	call	_Z41__static_initialization_and_destruction_0ii
	leave
	ret
.LFE1463:
.Lfe4:
	.size	_GLOBAL__I_main,.Lfe4-_GLOBAL__I_main
	.section	.ctors,"aw",@progbits
	.align 4
	.long	_GLOBAL__I_main
	.weak	pthread_mutex_unlock
	.weak	pthread_mutex_trylock
	.weak	pthread_mutex_lock
	.weak	pthread_create
	.weak	pthread_setspecific
	.weak	pthread_getspecific
	.weak	pthread_key_delete
	.weak	pthread_key_create
	.weak	pthread_once
	.section	.eh_frame,"a",@progbits
.Lframe1:
	.long	.LECIE1-.LSCIE1
.LSCIE1:
	.long	0x0
	.byte	0x1
	.string	"zP"
	.uleb128 0x1
	.sleb128 -4
	.byte	0x8
	.uleb128 0x5
	.byte	0x0
	.long	__gxx_personality_v0
	.byte	0xc
	.uleb128 0x4
	.uleb128 0x4
	.byte	0x88
	.uleb128 0x1
	.align 4
.LECIE1:
.LSFDE1:
	.long	.LEFDE1-.LASFDE1
.LASFDE1:
	.long	.LASFDE1-.Lframe1
	.long	.LFB1448
	.long	.LFE1448-.LFB1448
	.uleb128 0x0
	.byte	0x4
	.long	.LCFI0-.LFB1448
	.byte	0xe
	.uleb128 0x8
	.byte	0x85
	.uleb128 0x2
	.byte	0x4
	.long	.LCFI1-.LCFI0
	.byte	0xd
	.uleb128 0x5
	.align 4
.LEFDE1:
.LSFDE3:
	.long	.LEFDE3-.LASFDE3
.LASFDE3:
	.long	.LASFDE3-.Lframe1
	.long	.LFB1460
	.long	.LFE1460-.LFB1460
	.uleb128 0x0
	.byte	0x4
	.long	.LCFI3-.LFB1460
	.byte	0xe
	.uleb128 0x8
	.byte	0x85
	.uleb128 0x2
	.byte	0x4
	.long	.LCFI4-.LCFI3
	.byte	0xd
	.uleb128 0x5
	.align 4
.LEFDE3:
.LSFDE5:
	.long	.LEFDE5-.LASFDE5
.LASFDE5:
	.long	.LASFDE5-.Lframe1
	.long	.LFB1461
	.long	.LFE1461-.LFB1461
	.uleb128 0x0
	.byte	0x4
	.long	.LCFI6-.LFB1461
	.byte	0xe
	.uleb128 0x8
	.byte	0x85
	.uleb128 0x2
	.byte	0x4
	.long	.LCFI7-.LCFI6
	.byte	0xd
	.uleb128 0x5
	.align 4
.LEFDE5:
.LSFDE7:
	.long	.LEFDE7-.LASFDE7
.LASFDE7:
	.long	.LASFDE7-.Lframe1
	.long	.LFB1463
	.long	.LFE1463-.LFB1463
	.uleb128 0x0
	.byte	0x4
	.long	.LCFI9-.LFB1463
	.byte	0xe
	.uleb128 0x8
	.byte	0x85
	.uleb128 0x2
	.byte	0x4
	.long	.LCFI10-.LCFI9
	.byte	0xd
	.uleb128 0x5
	.align 4
.LEFDE7:
	.ident	"GCC: (GNU) 3.2.3 20030422 (Gentoo Linux 1.4 3.2.3-r2, propolice)"