Tweaks for Iterable.toList() invocations.

Tweaks for Iterable.toList() invocations.

R=brianwilkerson@google.com
BUG=

Committed: https://github.com/dart-lang/sdk/commit/c33d8cb1692382efe0f5e8372bf219cb92309ac2

[Brian Wilkerson, 2016-05-30 15:17:45]

lgtm

[scheglov, 2016-05-30 19:42:36]

Description was changed from

==========
Tweaks for Iterable.toList() invocations.

R=brianwilkerson@google.com
BUG=
==========

to

==========
Tweaks for Iterable.toList() invocations.

R=brianwilkerson@google.com
BUG=

Committed:
https://github.com/dart-lang/sdk/commit/c33d8cb1692382efe0f5e8372bf219cb92309ac2
==========

[scheglov, 2016-05-30 19:42:38]

Committed patchset #1 (id:1) manually as
c33d8cb1692382efe0f5e8372bf219cb92309ac2 (presubmit successful).

[sra1, 2016-05-31 06:43:56]

sra@google.com changed reviewers:
+ sra@google.com

[sra1, 2016-05-31 06:43:57]

https://codereview.chromium.org/2024543002/diff/1/pkg/analyzer/lib/src/dart/e...
File pkg/analyzer/lib/src/dart/element/element.dart (right):

https://codereview.chromium.org/2024543002/diff/1/pkg/analyzer/lib/src/dart/e...
pkg/analyzer/lib/src/dart/element/element.dart:4948: HashSet<LibraryElement>
visibleLibraries = new HashSet<LibraryElement>();
Ideally the default implementations would also be most efficient for normal
usage.

Do you have evidence that that this is not the case?
The VM implementation of LinkedHashSet (i.e. Set) is more storage-efficient that
HashSet for more than a 2-3 elements, but I don't know if that translates to
overall performance.

[scheglov, 2016-05-31 15:41:37]

https://codereview.chromium.org/2024543002/diff/1/pkg/analyzer/lib/src/dart/e...
File pkg/analyzer/lib/src/dart/element/element.dart (right):

https://codereview.chromium.org/2024543002/diff/1/pkg/analyzer/lib/src/dart/e...
pkg/analyzer/lib/src/dart/element/element.dart:4948: HashSet<LibraryElement>
visibleLibraries = new HashSet<LibraryElement>();
On 2016/05/31 06:43:56, sra1 wrote:
> Ideally the default implementations would also be most efficient for normal
> usage.
> 
> Do you have evidence that that this is not the case?
> The VM implementation of LinkedHashSet (i.e. Set) is more storage-efficient
that
> HashSet for more than a 2-3 elements, but I don't know if that translates to
> overall performance.
> 
> 


The following performance micro-benchmark uses 67 ms with Set, and 46 ms with
HashSet.
So it seems that HashSet wins.


---------------------
import 'dart:math';
import 'dart:collection';

main() {
  new Benchmark(100, () {
    for (int i = 0; i < 1000000; i++) {
//      HashSet<int> set = new HashSet<int>();
      Set<int> set = new Set<int>();
      set.add(1);
      set.add(2);
      set.toList(growable: false);
    }
  }).run();
}

typedef void BenchmarkIteration();

class Benchmark {
  final int iterationCount;
  final BenchmarkIteration iteration;

  Benchmark(this.iterationCount, this.iteration);

  void run() {
    int best = 1 << 20;
    for (int i = 0; i < iterationCount; i++) {
      Stopwatch sw = new Stopwatch()..start();
      iteration();
      best = min(sw.elapsedMilliseconds, best);
    }
    print('Best time: $best ms.');
  }
}
---------------------