C / C++ / MFC

    bool bTest = false;
    LARGE_INTEGER lFreq;
    LARGE_INTEGER lStart;
    LARGE_INTEGER lEnd;
    QueryPerformanceFrequency(&lFreq);
    QueryPerformanceCounter(&lStart);    
    _asm
    {
        push ecx
        mov ecx, 1000000000
_loop:
        cmp bTest, 0
        je  _set        
        sub ecx, 1
        jnz _loop
        jmp _end
_set:
        mov bTest, 1
        sub ecx, 1
        jnz _loop
_end:
        pop ecx
    }
    QueryPerformanceCounter(&lEnd);

    bool bTest = false;
    LARGE_INTEGER lFreq;
    LARGE_INTEGER lStart;
    LARGE_INTEGER lEnd;
    QueryPerformanceFrequency(&lFreq);
    QueryPerformanceCounter(&lStart);   
    _asm
    {
        push ecx
        mov ecx, 1000000000
_loop:
        mov bTest, 1        
        sub ecx, 1
        jnz _loop
        pop ecx
    }

    QueryPerformanceCounter(&lEnd);

With check (average of 8 runs):   1138972011 ns
Without check (average of 8 runs): 579320876 ns

static bool _bWasFooEverCalled = false; // set to true appropriately elsewhere
inline bool WasFooEverCalled()
{
	return _bWasFooEverCalled;
}

typedef void FooFunc();
void _FooFuncAndSetBool();
void _FooFuncWithoutSetBool();

bool bWasFooEverCalled = false;
FooFunc* pFooFunctionToCall = &_FooFuncAndSetBool;

void _FooFuncAndSetBool()
{
    bWasFooEverCalled = true;
    pFooFunctionToCall = &_FooFuncWithoutSetBool;
    _FooFuncWithoutSetBool();
}

void _FooFuncWithoutSetBool()
{
    // do something
}

inline void Foo()
{
    (*pFooFunctionToCall)();
}