Reordered class fields?

[bearophile]

D classes are free to reorder their fields, so maybe Bar1 should 
reorder its fields as Bar3, to save 4 bytes for each instance on 
32 bit systems:


class Bar1 {
     void Hello() {}
     float f;
     double d;
}
class Bar2 {
     void Hello() {}
     align(4) float f;
     align(4) double d;
}
class Bar3 {
     void Hello() {}
     double d;
     float f;
}
void main() {
     pragma(msg, __traits(classInstanceSize, Bar1)); // 24
     pragma(msg, __traits(classInstanceSize, Bar2)); // 20
     pragma(msg, __traits(classInstanceSize, Bar3)); // 20
}



This benchmark shows that if you allocate the class instances on 
the heap one at a time the total amount of memory used is the 
same for the various Bar (maybe because of the GC), so that 
optimization is useful for emplace() only and similar in-place 
allocations:


class Bar1 {
     void Hello() {}
     float f;
     double d;
}
class Bar2 {
     void Hello() {}
     align(4) float f;
     align(4) double d;
}
class Bar3 {
     void Hello() {}
     double d;
     float f;
}
int main() {
     pragma(msg, __traits(classInstanceSize, Bar1)); // 24
     pragma(msg, __traits(classInstanceSize, Bar2)); // 20
     pragma(msg, __traits(classInstanceSize, Bar3)); // 20
     //--------------
     //auto arr = new Bar1[1_000_000]; // 38.2 MB
     //auto arr = new Bar2[1_000_000]; // 38.2 MB
     auto arr = new Bar3[1_000_000]; // 38.2  MB
     foreach (ref a; arr)
         a = new typeof(arr[0])();
     int count;
     foreach (i; 0 .. 500_000_000) count++;
     return count;
}


So is such class field reordering worth an enhancement request in 
Bugzilla?

Bye,
bearophile