gcc-4.9 @ Arch Linux optimization for unused variables.

test1.c

int main(int argc, char *argv[])
{
	int i,j;
	i = 0;
	return 0;
}

test1.s

	.file	"test1.c"
	.text
	.globl	main
	.type	main, @function
main:
.LFB0:
	.cfi_startproc
	pushq	%rbp
	.cfi_def_cfa_offset 16
	.cfi_offset 6, -16
	movq	%rsp, %rbp
	.cfi_def_cfa_register 6
	movl	%edi, -20(%rbp)
	movq	%rsi, -32(%rbp)
	movl	$0, -4(%rbp)
	movl	$0, %eax
	popq	%rbp
	.cfi_def_cfa 7, 8
	ret
	.cfi_endproc
.LFE0:
	.size	main, .-main
	.ident	"GCC: (GNU) 4.9.0 20140521 (prerelease)"
	.section	.note.GNU-stack,"",@progbits

test2.c

int main(int argc, char *argv[])
{
	int i;
	i = 0;
	return 0;
}

test2.s

	.file	"test2.c"
	.text
	.globl	main
	.type	main, @function
main:
.LFB0:
	.cfi_startproc
	pushq	%rbp
	.cfi_def_cfa_offset 16
	.cfi_offset 6, -16
	movq	%rsp, %rbp
	.cfi_def_cfa_register 6
	movl	%edi, -20(%rbp)
	movq	%rsi, -32(%rbp)
	movl	$0, -4(%rbp)
	movl	$0, %eax
	popq	%rbp
	.cfi_def_cfa 7, 8
	ret
	.cfi_endproc
.LFE0:
	.size	main, .-main
	.ident	"GCC: (GNU) 4.9.0 20140521 (prerelease)"
	.section	.note.GNU-stack,"",@progbits

test3.c

int main(int argc, char *argv[])
{
	int i,j;
	i = 0;
	j = 0;
	return 0;
}

test3.s

	.file	"test3.c"
	.text
	.globl	main
	.type	main, @function
main:
.LFB0:
	.cfi_startproc
	pushq	%rbp
	.cfi_def_cfa_offset 16
	.cfi_offset 6, -16
	movq	%rsp, %rbp
	.cfi_def_cfa_register 6
	movl	%edi, -20(%rbp)
	movq	%rsi, -32(%rbp)
	movl	$0, -4(%rbp)
	movl	$0, -8(%rbp)
	movl	$0, %eax
	popq	%rbp
	.cfi_def_cfa 7, 8
	ret
	.cfi_endproc
.LFE0:
	.size	main, .-main
	.ident	"GCC: (GNU) 4.9.0 20140521 (prerelease)"
	.section	.note.GNU-stack,"",@progbits