関数ローカルのstatic変数の仕組み。

StaticTest.asm

; Function compile flags: /Ogtpy
; File c:\data\test\statictest.cpp
;    COMDAT ?StaticTest@@YAHXZ
_TEXT	SEGMENT
?StaticTest@@YAHXZ PROC					; StaticTest, COMDAT

; 6    : 	static int s = std::rand();

	mov	eax, DWORD PTR ?$S1@?1??StaticTest@@YAHXZ@4IA
	test	al, 1
	jne	SHORT $LN4@StaticTest
	or	eax, 1
	mov	DWORD PTR ?$S1@?1??StaticTest@@YAHXZ@4IA, eax
	call	_rand

; 7    : 	return ++s;

	inc	eax
	mov	DWORD PTR ?s@?1??StaticTest@@YAHXZ@4HA, eax

; 8    : }

	ret	0
$LN4@StaticTest:

; 7    : 	return ++s;

	mov	eax, DWORD PTR ?s@?1??StaticTest@@YAHXZ@4HA
	inc	eax
	mov	DWORD PTR ?s@?1??StaticTest@@YAHXZ@4HA, eax

; 8    : }

	ret	0
?StaticTest@@YAHXZ ENDP					; StaticTest
_TEXT	ENDS

StaticTest.cpp

// call "%VS110COMNTOOLS%vsvars32.bat" & cl /O2 /Fa /FAs StaticTest.cpp
#include <cstdio>
#include <cstdlib>
int StaticTest() {
    static int s = std::rand();
	return ++s;
}
int main() {
	std::printf("%d", StaticTest());
}