C++: Structs slower to access than basic variables?

Question

I found some code that had \"optimization\" like this:

void somefunc(SomeStruct param){
    float x = param.x; // param.x and x are both floats. supposedly this          


        

Answer 1

I'm no compiler guru, so take this with a grain of salt. I'm guessing that the original author of the code is assuming that by copying the values from the struct into local variables, the compiler has "placed" those variables into floating point registers which are available on some platforms (e.g., x86). If there aren't enough registers to go around, they'd be put in the stack.

That being said, unless this code was in the middle of an intensive computation/loop, I'd strive for clarity rather than speed. It's pretty rare that anyone is going to notice a few instructions difference in timing.