Optimizations for hashCode.

editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/element/ElementImpl.java

Index: editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/element/ElementImpl.java
diff --git a/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/element/ElementImpl.java b/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/element/ElementImpl.java
index 5910023d67b2978ae2c15de57b7e06d826639ae4..8113ee98ebb287e0ac99495f757f851fe457912f 100644
--- a/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/element/ElementImpl.java
+++ b/editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/element/ElementImpl.java
@@ -198,7 +198,13 @@ public abstract class ElementImpl implements Element {
     // TODO: We might want to re-visit this optimization in the future.
     // We cache the hash code value as this is a very frequently called method.
     if (cachedHashCode == 0) {
-      cachedHashCode = getLocation().hashCode();
+      int hashIdentifier = getIdentifier().hashCode();

[Brian Wilkerson, 2014/03/21 14:04:14]

ElementLocation goes to extra work to not include the URI kind in the hash code
for compilation units and libraries (I'm not sure why HtmlElements aren't using
their source as their location, that might be a bug). I think we need to
preserve that here (or implement this as

public int hashCode() {
  if (cachedHashCode == 0) {
    cachedHashCode = computeHashCode();
  }
  return cachedHashCode;
}

and override computeHashCode in appropriate subclasses).

[scheglov, 2014/03/21 16:41:10]

1. Most ElementImpl use new implementation.
2. LibraryElementImpl delegates to its defining compilation unit.
3. CompilationUnitImpl delegates to its Source.
4. FileBaseSource does not use the kind in its hashCode implementation.

+      Element enclosing = getEnclosingElement();
+      if (enclosing != null) {
+        cachedHashCode = hashIdentifier + enclosing.hashCode();

[Brian Wilkerson, 2014/03/21 14:04:14]

ElementLocation used a more complex calculation for combining hash codes. Does
combining them this way increase or lessen the probability of hash collisions?

[scheglov, 2014/03/21 16:41:10]

Done.

[scheglov, 2014/03/21 16:55:05]

Actually I spoke too fast.
It costs about 100 ms of the additional time on dart2js analysis using
Dart-based analyzer.

+      } else {
+        cachedHashCode = hashIdentifier;
+      }
     }
     return cachedHashCode;
   }