Don't always call _copyFromObjectArray.

runtime/lib/array.dart

Index: runtime/lib/array.dart
diff --git a/runtime/lib/array.dart b/runtime/lib/array.dart
index 1d49d3b746dfbd89e26907d792db0239e35aa8ef..0f06c9493a78360b713e552c0e7d4b8a4f697ec5 100644
--- a/runtime/lib/array.dart
+++ b/runtime/lib/array.dart
@@ -66,22 +66,21 @@ class _List<E> implements List<E> {
     }
     int length = end - start;
     if (length == 0) return;
-
-    if (ClassID.getID(iterable) == ClassID.cidOneByteString) {
+    if (identical(this, iterable)) {
+      Lists.copy(iterable, skipcount, this, start, length);
+    } else if (ClassID.getID(iterable) == ClassID.cidArray && length > 128) {

[srdjan, 2014/09/02 18:33:58]

Please add parentheses.

       _copyFromObjectArray(iterable, skipCount, start, length);

[Lasse Reichstein Nielsen, 2014/09/02 14:29:09]

Good thing this wasn't called before due to the incorrect ClassID - it could do
the wrong thing if called with itself.

Currently, I'm not sure this call ever pays for itself, I'll have to check it
again when _copyFromObjectArray has been optimized.

+    } else if (iterable is List) {
+      Lists.copy(iterable, skipCount, this, start, length);
     } else {
-      if (iterable is List) {
-        Lists.copy(iterable, skipCount, this, start, length);
-      } else {
-        Iterator it = iterable.iterator;
-        while (skipCount > 0) {
-          if (!it.moveNext()) return;
-          skipCount--;
-        }
-        for (int i = start; i < end; i++) {
-          if (!it.moveNext()) return;
-          this[i] = it.current;
-        }
+      Iterator it = iterable.iterator;
+      while (skipCount > 0) {
+        if (!it.moveNext()) return;
+        skipCount--;
+      }
+      for (int i = start; i < end; i++) {
+        if (!it.moveNext()) return;
+        this[i] = it.current;
       }
     }
   }
@@ -104,7 +103,13 @@ class _List<E> implements List<E> {
     int length = end - start;
     if (start == end) return <E>[];
     List list = new _List(length);
-    list._copyFromObjectArray(this, start, 0, length);
+    if (length < 128) {

[Vyacheslav Egorov (Google), 2014/09/02 14:31:15]

I don't like that this is repeated. 

Can we have a _copyArray() somewhere that does

if (length < ...) {
  // ... do this ...
} else {
  list._copyFromObjectArray(...)
}

?

This will open possibilities for uniform optimizations instead of searching for
other places that use it...

+      for (int i = 0; i < length; i++) {
+        list[i] = this[start + i];
+      }
+    } else {
+      list._copyFromObjectArray(this, start, 0, length);
+    }
     var result = new _GrowableList<E>.withData(list);
     result._setLength(length);
     return result;
@@ -257,7 +262,13 @@ class _List<E> implements List<E> {
     var length = this.length;
     if (length > 0) {
       var result = growable ? new _List(length) : new _List<E>(length);
-      result._copyFromObjectArray(this, 0, 0, length);
+      if (length < 128) {
+        for (int i = 0; i < length; i++) {
+          result[i] = this[i];
+        }
+      } else {
+        result._copyFromObjectArray(this, 0, 0, length);
+      }
       if (growable) {
         result = new _GrowableList<E>.withData(result);
         result._setLength(length);