Насчет того как узнать, можно например дебаггером посмотреть

// nevill.cpp : Defines the entry point for the console application.
//
#include <iostream.h>

//using namespace std;


inline int even(int a){

return ! (a%2);

}



int main()
{
if(even(10)) cout << "true" <<endl;else cout << "false" <<endl;

return 0;
}

0040106A call @ILT+20(even) (00401019)
0040106F add esp,4
00401072 test eax,eax
00401074 je main+43h (00401093)
00401076 push offset @ILT+10(endl) (0040100f)
0040107B push offset string "true" (00425024)
00401080 mov ecx,offset cout (004289c0)
00401085 call ostream::operator<< (00401470)
0040108A mov ecx,eax
0040108C call @ILT+0(ostream::operator<<) (00401005)
00401091 jmp main+5Eh (004010ae)
00401093 push offset @ILT+10(endl) (0040100f)
00401098 push offset string "false" (0042501c)
0040109D mov ecx,offset cout (004289c0)
004010A2 call ostream::operator<< (00401470)
004010A7 mov ecx,eax
004010A9 call @ILT+0(ostream::operator<<) (00401005)
19:
20: return 0;
004010AE xor eax,eax
21: }
004010B0 pop edi
004010B1 pop esi
004010B2 pop ebx
004010B3 add esp,40h
004010B6 cmp ebp,esp
004010B8 call __chkesp (00403550)
004010BD mov esp,ebp
004010BF pop ebp
004010C0 ret

Microsoft Specific

The __inline keyword is equivalent to inline.

Even with __forceinline, the compiler cannot inline code in all circumstances. The compiler cannot inline a function if:

The function or its caller is compiled with /Ob0 (the default option for debug builds).
The function and the caller use different types of exception handling (C++ exception handling in one, structured exception handling in the other).
The function has a variable argument list.
The function uses inline assembly, unless compiled with /Og, /Ox, /O1, or /O2.
The function returns an unwindable object by value, when compiled with /GX, /EHs, or /EHa.
The function receives an unwindable copy-constructed object passed by value, when compiled with /GX, /EHs,, or /EHa.
The function is recursive and not accompanied by #pragma inline_recursion(on). With the pragma, recursive functions can be inlined to a default depth of eight calls. To change the inlining depth, use inline_depth pragma.
The function is virtual and is called virtually. Direct calls to virtual functions can be inlined.
The program takes the address of the function and the call is made via the pointer to the function. Direct calls to functions that have had their address taken can be inlined.
The function is also marked with the naked __declspec modifier.
If the compiler cannot inline a function declared with __forceinline, it generates a level 1 warning (4714).

Recursive functions can be substituted inline to a depth specified by the inline_depth pragma. After that depth, recursive function calls are treated as calls to an instance of the function. The inline_recursion pragma controls the inline expansion of a function currently under expansion. See the Inline-Function Expansion (/Ob) compiler option for related information.

END Microsoft Specific