Optimizations for hashCode.

Optimizations for hashCode.

This improves Dart-based analyzer performance.

dart2js:   12500 -> 11600 ms, about 900 ms or 7%.
blueshift: 23500 -> 21500 ms, about 2000 ms or 8%.

R=brianwilkerson@google.com
BUG=

Committed: https://code.google.com/p/dart/source/detail?r=34318

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

https://codereview.chromium.org/207853002/diff/1/editor/tools/plugins/com.goo...
File
editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/element/ElementImpl.java
(right):

https://codereview.chromium.org/207853002/diff/1/editor/tools/plugins/com.goo...
editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/element/ElementImpl.java:201:
int hashIdentifier = getIdentifier().hashCode();
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).

https://codereview.chromium.org/207853002/diff/1/editor/tools/plugins/com.goo...
editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/element/ElementImpl.java:204:
cachedHashCode = hashIdentifier + enclosing.hashCode();
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]

https://codereview.chromium.org/207853002/diff/1/editor/tools/plugins/com.goo...
File
editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/element/ElementImpl.java
(right):

https://codereview.chromium.org/207853002/diff/1/editor/tools/plugins/com.goo...
editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/element/ElementImpl.java:201:
int hashIdentifier = getIdentifier().hashCode();
On 2014/03/21 14:04:14, Brian Wilkerson wrote:
> 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).

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.

https://codereview.chromium.org/207853002/diff/1/editor/tools/plugins/com.goo...
editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/element/ElementImpl.java:204:
cachedHashCode = hashIdentifier + enclosing.hashCode();
On 2014/03/21 14:04:14, Brian Wilkerson wrote:
> ElementLocation used a more complex calculation for combining hash codes. Does
> combining them this way increase or lessen the probability of hash collisions?

Done.

[scheglov, 2014-03-21 16:55:04]

https://codereview.chromium.org/207853002/diff/1/editor/tools/plugins/com.goo...
File
editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/element/ElementImpl.java
(right):

https://codereview.chromium.org/207853002/diff/1/editor/tools/plugins/com.goo...
editor/tools/plugins/com.google.dart.engine/src/com/google/dart/engine/internal/element/ElementImpl.java:204:
cachedHashCode = hashIdentifier + enclosing.hashCode();
On 2014/03/21 16:41:10, scheglov wrote:
> On 2014/03/21 14:04:14, Brian Wilkerson wrote:
> > ElementLocation used a more complex calculation for combining hash codes.
Does
> > combining them this way increase or lessen the probability of hash
collisions?
> 
> Done.

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

[Brian Wilkerson, 2014-03-24 17:49:54]

LGTM

[scheglov, 2014-03-24 18:18:19]

Committed patchset #1 manually as r34318 (presubmit successful).