Improve string library performance. String concat and indexOf.

runtime/lib/string_patch.dart

Index: runtime/lib/string_patch.dart
===================================================================
--- runtime/lib/string_patch.dart	(revision 29294)
+++ runtime/lib/string_patch.dart	(working copy)
@@ -84,12 +84,12 @@
     if (identical(this, other)) {
       return true;
     }
-    if ((other is !String) ||
+    // TODO(5413632): Compare hash codes when both are present.

[Ivan Posva, 2013/10/28 23:35:09]

I don't think comparing hash codes is effective, as I don't think you get them
frequently enough. So we might want to just remove this TODO.

[srdjan, 2013/10/29 17:02:29]

Done.

+    if ((other is! String) ||
         (this.length != other.length)) {
-      // TODO(5413632): Compare hash codes when both are present.
       return false;
     }
-    final len = this.length;
+    final int len = this.length;

[Ivan Posva, 2013/10/28 23:35:09]

?

[srdjan, 2013/10/29 17:02:29]

Removed type.

     for (int i = 0; i < len; i++) {
       if (this.codeUnitAt(i) != other.codeUnitAt(i)) {
         return false;
@@ -424,7 +424,7 @@
     if (isOneByteString) {
       return _OneByteString._concatAll(stringList, totalLength);
     }
-    return _concatAllNative(stringList, 0, stringList.length);
+    return _concatRangeNative(stringList, 0, stringList.length);
   }
 
   Iterable<Match> allMatches(String str) {
@@ -509,10 +509,31 @@
 
   String toLowerCase() native "String_toLowerCase";
 
+  // Concatenate ['start', 'end'[ elements of 'strings'. 'strings' must contain
+  // String elements. Optimized for OneByteStrings.
+  static String _concatRange(List<String> strings, int start, int end) {
+    if ((end - start) == 1) {
+      return strings[start];
+    }
+    final int numValues = strings.length;
+    if (start == 0 && (end == numValues)) {

[Ivan Posva, 2013/10/28 23:35:09]

(start == 0)

[srdjan, 2013/10/29 17:02:29]

Done.

+      int totalLength = 0;
+      for (int i = 0; i < numValues; i++) {
+        String s = strings[i];
+        if (s._cid != _OneByteString._classId) {
+          return _concatRangeNative(strings, start, end);
+        }
+        totalLength += s.length;
+      }
+      return _OneByteString._concatAll(strings, totalLength);
+    }
+    return _concatRangeNative(strings, start, end);
+  }
+
   // Call this method if not all list elements are known to be OneByteString(s).
   // 'strings' must be an _List or _GrowableList.
-  static String _concatAllNative(List<String> strings, int start, int end)
-      native "Strings_concatAll";
+  static String _concatRangeNative(List<String> strings, int start, int end)
+      native "String_concatRange";
 }
 
 
@@ -548,11 +569,11 @@
   }
 
   // All element of 'strings' must be OneByteStrings.
-  static _concatAll(_List<String> strings, int totalLength) {
+  static _concatAll(List<String> strings, int totalLength) {
     // TODO(srdjan): Improve code below and raise or eliminate the limit.
     if (totalLength > 128) {
       // Native is quicker.
-      return _StringBase._concatAllNative(strings, 0, strings.length);
+      return _StringBase._concatRangeNative(strings, 0, strings.length);
     }
     var res = _OneByteString._allocate(totalLength);
     final stringsLength = strings.length;
@@ -567,6 +588,23 @@
     return res;
   }
 
+  int indexOf(Pattern pattern, [int start = 0]) {
+    final int len = this.length;

[Ivan Posva, 2013/10/28 23:35:09]

Not sure whether we should be using this. or not. Also no types inside methods.

[srdjan, 2013/10/29 17:02:29]

The name' length' is too generic, therefore I feel it makes in this case for a
more readable code. Let me know if you disagree.

+    // Specialize for single character pattern.
+    if ((pattern._cid == _OneByteString._classId) &&

[Ivan Posva, 2013/10/28 23:35:09]

What about an ExternalOneByteString?

[srdjan, 2013/10/29 17:02:29]

Added: TODO. The inner loop should stay monomorphic. Will need to add a test.

+        (pattern.length == 1) &&
+        (start >= 0) && (start < len)) {
+      final int patternCu0 = pattern.codeUnitAt(0);

[Ivan Posva, 2013/10/28 23:35:09]

Another quick test you could do: If the pattern is outside of the one byte
string range then you will not find it.

[srdjan, 2013/10/29 17:02:29]

Good idea, once I allow two byte strings.

+      for (int i = start; i < len; i++) {
+        if (this.codeUnitAt(i) == patternCu0) {
+          return i;
+        }
+      }
+      return -1;
+    }
+    return super.indexOf(pattern, start);
+  }
+
   // Allocates a string of given length, expecting its content to be
   // set using _setAt.
   static _OneByteString _allocate(int length) native "OneByteString_allocate";