CODEWITHSUNDEEP
c++optimization
Cpp Man
Cpp Man

Reputation: 108

Is this a common optimization?

If I have code like this:

{
   int x = f();

   if (g(x)) return;

   int y = h();

   // use y
}

Will the compiler probably realize that x is not used after the if statement and that it can put the variable y in the register that x occupied? I know that all compilers are different, but the question is whether this is a common optimization that I can reasonably rely on. I am wondering because I want to let the optimizer elide the extra registers rather than having to come up with names like this_variable_holds_x_then_y.

Would it help to add an extra scope around x so that the compiler can see it's inaccessible from outside it?

Upvotes: 2

Views: 103

Answers (1)

Tony Delroy
Tony Delroy

Reputation: 106096

Yes - it's a very simple optimisation that any modern compiler would do. You can also check easily for yourself - most compilers support a "-S" or other command-line option that produces assembly language output (or you can disassemble the machine code).

Upvotes: 2

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