Thread: speed/optimization concerns

Alright, I'll admit, I'm somewhat anal retentive when it comes to optimizing my code and getting it to run fast without using more memory than it must, but I don't see that as a bad thing Anyway, I was wondering if anyone knows which would run faster (excuse the vague code, it's just meant as an example)

Code:

int a()
{
    return(42);
}

Now, which b() is faster?

Code:

int b()
{
    int temp;

    temp=a();
    c(temp);
}

or

Code:

int b()
{
    c(a());
}

I'm guessing that the second one is, but I'm not sure, and I don't know exactly how the compiler changes the code around for optimizations and such... thanks.

What is c???
Generally, the second should be faster due to the declaration of a temporary variable. However, to be absolutely sure, compile both then use a disassembler to look at the assembly code.

First:

call - 19 clks
mov - 9 clks
mov - 9 clks
push - 11 clks
call - 19 clks
add - 3 clks

Sum: 70 clks

Second:

call - 19 clks
push - 11 clks
call - 19 clks
add - 3 clks

Sum: 52 clks


Conclusion:

The second is ~25% faster than the first.
The first is ~34% slower than the second.

PS:
I was really bored, I know .

It heavily depends on compiler and optimization settings. Also, you should always try to find the bottlenecks of your program first and optimize that part, as a performance boost there might make your program visibly faster while a performance boost somewhere else might be wasted time.