Which one works faster?

Mani Kazemi

Do these 2 have any differences?

if (condition)
{
    std::cout << "Condition is true";
}
else
{
    std::cout << "Condition is false";
}

if (condition)
{
    std::cout << "Condition is true";
    return 0;
}
std::cout << "Condition is false";

I know that is not good to use the second one because maybe you have some more code after it. But at the end of the code that we don't have anything after that else, isn't it better to use the second one?

Shao-Chuan Wang

I modified the original question a bit as follows,

void f1() {
    int a = 0;
    if (a > 0) {
        a = 1;
    } else {
        a = 2;
    }
}

void f2() {
    int a = 0;
    if (a > 0) {
        a = 1;
        return;
    } 
    a = 2;
}

Here are the compiled assembly. f1() and f2() are nearly identical.

f1():
        push    rbp
        mov     rbp, rsp
        mov     DWORD PTR [rbp-4], 0
        cmp     DWORD PTR [rbp-4], 0
        jle     .L2
        mov     DWORD PTR [rbp-4], 1
        jmp     .L4
.L2:
        mov     DWORD PTR [rbp-4], 2
.L4:
        nop
        pop     rbp
        ret
f2():
        push    rbp
        mov     rbp, rsp
        mov     DWORD PTR [rbp-4], 0
        cmp     DWORD PTR [rbp-4], 0
        jle     .L6
        mov     DWORD PTR [rbp-4], 1
        jmp     .L5
.L6:
        mov     DWORD PTR [rbp-4], 2
.L5:
        pop     rbp
        ret

The only difference is that .L4 has a nop. More details can be found here.

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