Update _d_arrayctor branches to improve performance (#21675)

Author: Albert24GG

druntime/src/core/internal/array/construction.d

@@ -65,7 +65,7 @@ Tarr _d_arrayctor(Tarr : T[], T)(return scope Tarr to, scope Tarr from, char* ma
 
     enforceRawArraysConformable("initialization", T.sizeof, vFrom, vTo);
 
-    static if (hasElaborateCopyConstructor!T)
+    static if (__traits(hasCopyConstructor, T))
     {
         size_t i;
         try
@@ -88,8 +88,30 @@ Tarr _d_arrayctor(Tarr : T[], T)(return scope Tarr to, scope Tarr from, char* ma
     }
     else
     {
-        // blit all elements at once
-        memcpy(cast(void*) to.ptr, from.ptr, to.length * T.sizeof);
+        if (to.length)
+        {
+            // blit all elements at once
+            memcpy(cast(void*) to.ptr, from.ptr, to.length * T.sizeof);
+
+            // call postblits if they exist
+            static if (__traits(hasPostblit, T))
+            {
+                import core.internal.lifetime : __doPostblit;
+                size_t i = 0;
+                try __doPostblit(to, i);
+                catch (Exception o)
+                {
+                    // Destroy, in reverse order, what we've constructed so far
+                    while (i--)
+                    {
+                        auto elem = cast(Unqual!T*) &to[i];
+                        destroy(*elem);
+                    }
+
+                    throw o;
+                }
+            }
+        }
     }
 
     return to;

druntime/src/core/internal/lifetime.d

@@ -210,14 +210,29 @@ void __doPostblit(T)(T[] arr)
     {
         static if (__traits(isStaticArray, T) && is(T : E[], E))
             __doPostblit(cast(E[]) arr);
-        else static if (!__traits(compiles, arr[0].__xpostblit))
+        else
         {
-            alias Unqual_T = Unqual!T;
-            foreach (ref elem; (() @trusted => cast(Unqual_T[]) arr)())
+            import core.internal.traits : Unqual;
+            foreach (ref elem; (() @trusted => cast(Unqual!T[]) arr)())
                 elem.__xpostblit();
         }
+    }
+}
+
+// ditto, but with an index to keep track of how many elements have been postblitted
+void __doPostblit(T)(T[] arr, ref size_t i)
+{
+    // infer static postblit type, run postblit if any
+    static if (__traits(hasPostblit, T))
+    {
+        static if (__traits(isStaticArray, T) && is(T : E[], E))
+            __doPostblit(cast(E[]) arr, i);
         else
-            foreach (ref elem; arr)
-                elem.__xpostblit();
+        {
+            i = 0;
+            import core.internal.traits : Unqual;
+            for(auto eptr = cast(Unqual!T*)&arr[0]; i < arr.length; ++i, ++eptr)
+                eptr.__xpostblit();
+        }
     }
 }