A trouble with constructors

[bearophile]

While optimizing some code I have seen that adding a basic struct constructor produces a large difference in performance, this is a test program:


enum bool use_ctor = true;
struct Foo {
    static if (use_ctor) {
        double x, y, z;

        pure nothrow this(double x_, double y_, double z_) {
            this.x = x_;
            this.y = y_;
            this.z = z_;
        }
    } else {
        double x=0.0, y=0.0, z=0.0;
    }

    Foo muls(double s) {
        return Foo(this.x*s, this.y*s, this.z*s);
    }
}
void main() {}


Changing use_ctor from true to false changes a lot the amount of asm code produced and the performance of a program that uses this structs.

For asm listings and more info click here:
http://d.puremagic.com/issues/show_bug.cgi?id=5254

Bye,
bearophile