Optimize _GrowableArray._join and _StringBase._interpolate.

runtime/lib/string_patch.dart

Index: runtime/lib/string_patch.dart
diff --git a/runtime/lib/string_patch.dart b/runtime/lib/string_patch.dart
index 9a454b114da22988e9e3ccbb692b605011f8ea72..ff88095d9eb0893f2b2a822af3696785167c0626 100644
--- a/runtime/lib/string_patch.dart
+++ b/runtime/lib/string_patch.dart
@@ -530,28 +530,36 @@ class _StringBase {
   /**
    * Convert all objects in [values] to strings and concat them
    * into a result string.
+   * Modifies the input list if it contains non-`String` values.
    */
-  static String _interpolate(List<String> values) {
+  static String _interpolate(final List values) {
     final numValues = values.length;
-    _List stringList = new List<String>(numValues);
-    bool isOneByteString = true;
     int totalLength = 0;
-    for (int i = 0; i < numValues; i++) {
-      var s = values[i].toString();
-      if (isOneByteString && (ClassID.getID(s) == ClassID.cidOneByteString)) {
+    int i = 0;
+    while (i < numValues) {
+      final e = values[i];
+      final s = e.toString();
+      values[i] = s;
+      if (ClassID.getID(s) == ClassID.cidOneByteString) {
         totalLength += s.length;
+        i++;
+      } else if (s is! String) {
+        throw new ArgumentError(s);
       } else {
-        isOneByteString = false;
-        if (s is! String) {
-          throw new ArgumentError(s);
+        // Handle remaining elements without checking for one-byte-ness.
+        while (++i < numValues) {
+          final e = values[i];
+          final s = e.toString();
+          values[i] = s;
+          if (s is! String) {
+            throw new ArgumentError(s);
+          }
         }
+        return _concatRangeNative(values, 0, numValues);
       }
-      stringList[i] = s;
-    }
-    if (isOneByteString) {
-      return _OneByteString._concatAll(stringList, totalLength);
     }
-    return _concatRangeNative(stringList, 0, stringList.length);
+    // All strings were one-byte strings.
+    return _OneByteString._concatAll(values, totalLength);
   }
 
   Iterable<Match> allMatches(String string, [int start = 0]) {
@@ -669,6 +677,29 @@ class _OneByteString extends _StringBase implements String {
     return super == other;
   }
 
+  String operator +(String other) {
+    if (ClassID.getID(other) != ClassID.cidOneByteString) {
+      return super + other;
+    }

[Florian Schneider, 2014/09/25 11:14:45]

I would really like this to be specialized for external one- and both kinds of
two-byte strings as well. On the other hand we may not want to duplicate this
whole method 4 times.

How is performance if you factor the code below here out into a common helper,
and add operator+ to all concrete String classes?

[Lasse Reichstein Nielsen, 2014/09/30 09:17:45]

I think I'll revert this operator for now and do some more tests.
It's no longer used in interpolate, so it really is a separate change.

+    final thisLength = this.length;
+    final otherLength = other.length;
+    final length = thisLength + otherLength;
+    if (length > 128) {
+      final list = new _List(2);
+      list[0] = this;
+      list[1] = other;
+      return _concatAll(list, length);
+    }
+    final _OneByteString result = _allocate(length);
+    for (int i = 0; i < thisLength; i++) {
+      result._setAt(i, this.codeUnitAt(i));
+    }
+    for (int i = 0; i < otherLength; i++) {
+      result._setAt(thisLength + i, other.codeUnitAt(i));
+    }
+    return result;
+  }
+
   String _substringUncheckedNative(int startIndex, int endIndex)
       native "OneByteString_substringUnchecked";
 
@@ -690,11 +721,11 @@ class _OneByteString extends _StringBase implements String {
       // Native is quicker.
       return _StringBase._concatRangeNative(strings, 0, strings.length);
     }
-    var res = _OneByteString._allocate(totalLength);
+    final res = _OneByteString._allocate(totalLength);
     final stringsLength = strings.length;
     int rIx = 0;
     for (int i = 0; i < stringsLength; i++) {
-      _OneByteString e = strings[i];
+      final _OneByteString e = strings[i];
       final eLength = e.length;
       for (int s = 0; s < eLength; s++) {
         res._setAt(rIx++, e.codeUnitAt(s));