Strange GCC Behaviour

Question

Given the following C++ code:

struct vertex_type {
    float x, y, z;

    //vertex_type() {}
    //vertex_type(float x, float y, float z) : x(x), y(y), z(z) {}
         


        

Answer 1

If you have custom constructor, the compiler should call it for all vector it create. If you don't write your own, it default to a generated constructor. But as no type are complex, it just don't need to call it. And the array is store as a constant table in the binary.

Try inlining your default constructor and let it empty. Of course, it may only work wit h optimization enabled

Answer 2

This is a long-standing missing optimization in GCC. It should be able to generate the same code for both cases, but it can't.

Without the constructors, your vertex_type is a POD structure, which GCC can initialize static/global instances of at compile time. With the constructors, the best it can do is generate code to initialize the global at program startup.