CODEWITHSUNDEEP
c++memory-managementcompiler-optimization
Edoren
Edoren

Reputation: 83

Compiler Optimization - Variable Memory Usage

When I make a function most of the time I make a lot of variables inside of it, just because its easier to debug the code.

Lets say I have this function:

void foo(int value) {
    int x = value * 1;
    int y = value * 2;
    int z = value * 3;

    int u = x + 1;
    int v = y + 2;
    int w = z + 3;
}

This code is fine and its easy to debug (you can see step by step what is happening) but its using a lot of memory (28 bytes considering that each int is 4 bytes), and it could be optimized in this way:

void foo(int value) {
    int u = value * 1 + 1;
    int v = value * 2 + 2;
    int w = value * 3 + 3;
}

Based on this I have some questions:

  1. Does the compiler make this kind of optimizations in release builds?.
  2. Does it reuse the memory of variables that are not used anymore in the function to avoid using more registers?.

Upvotes: 1

Views: 91

Answers (1)

Jesper Juhl
Jesper Juhl

Reputation: 31467

Yes. A modern compiler will remove those intermediate variables. Yes. A modern compiler will fold constants and reuse registers and memory locations.

In short; don't worry about stuff at this level, the compiler will fix it. Instead worry about writing readable code and algorithmic improvements and leave the details to the compiler - it's pretty smart these days ;)

Upvotes: 3

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