Reapply "Improve hashCode for closure objects" with fixes.

Reapply "Improve hashCode for closure objects" with fixes.

This CL includes the following fixes:
* Fix for incorrect non-nullable assumption about _Closure._hash field.
* Add error handling into BecomeMapTraits::Hash.
* Correct assertions for validating layout of Closure objects.
* Add identityHashCode to the list of VM entry points in precompiler.

Closes #30211.

Original code review:

https://codereview.chromium.org/2983823002/

Original CL description:

This performance improvement is inspired by Flutter listeners stored in
the HashSet (see ObserverList) and frequently checked using
HashSet.contains(). If there are many such listeners and they are
implicit instance closures (for example, created by
'new Listenable.merge(...)'), HashSet.contains() becomes very slow.
It spends a lot of time in Closure_equals native method due to hash
collisions between closure objects with same function
but different receivers.

This CL improves hashCode() calculation for implicit instance closures
by mixing function hashcode with identity hashcode of the receiver.
For explicit closures and static implicit closures hashCode() is
improved by using identityHashCode() of a closure object.

Also, hashcode is calculated once and cached in each closure instance.
The size of a closure instance doesn't grow up because there was unused
word-size padding both on 32-bit and 64-bit architectures.

The execution time of the following micro-benchmark is reduced from
47665ms to 135ms on my Linux/x64 box.

-------------------------------------

import "dart:collection";

class Foo {
  int _a;
  Foo(this._a);
  void bar() {}
}

main() {
  HashSet hs = new HashSet();
  for (int i = 0; i < 1000; ++i) {
    hs.add(new Foo(i).bar);
  }

  var watch = new Stopwatch()..start();

  for (int i = 0; i < 1000; ++i) {
    for (var c in hs) {
      hs.contains(c);
    }
  }

  int time = watch.elapsedMilliseconds;
  print("Time: ${time}ms\n");
}

-------------------------------------

R=zra@google.com

Committed: https://github.com/dart-lang/sdk/commit/203955bc48fdbd03b7b030c4e6dbcd20920201ec

[alexmarkov, 2017-07-20 21:45:11]

alexmarkov@google.com changed reviewers:
+ asiva@google.com, zra@google.com

[zra, 2017-07-20 21:55:51]

lgtm

[alexmarkov, 2017-07-20 22:22:23]

Description was changed from

==========
Reapply "Improve hashCode for closure objects" with fixes.

This CL includes the following fixes:
* Fix for incorrect non-nullable assumption about _Closure._hash field.
* Add error handling into BecomeMapTraits::Hash.
* Correct assertions for validating layout of Closure objects.
* Add identityHashCode to the list of VM entry points in precompiler.

Closes #30211.

Original code review:

https://codereview.chromium.org/2983823002/

Original CL description:

This performance improvement is inspired by Flutter listeners stored in
the HashSet (see ObserverList) and frequently checked using
HashSet.contains(). If there are many such listeners and they are
implicit instance closures (for example, created by
'new Listenable.merge(...)'), HashSet.contains() becomes very slow.
It spends a lot of time in Closure_equals native method due to hash
collisions between closure objects with same function
but different receivers.

This CL improves hashCode() calculation for implicit instance closures
by mixing function hashcode with identity hashcode of the receiver.
For explicit closures and static implicit closures hashCode() is
improved by using identityHashCode() of a closure object.

Also, hashcode is calculated once and cached in each closure instance.
The size of a closure instance doesn't grow up because there was unused
word-size padding both on 32-bit and 64-bit architectures.

The execution time of the following micro-benchmark is reduced from
47665ms to 135ms on my Linux/x64 box.

-------------------------------------

import "dart:collection";

class Foo {
  int _a;
  Foo(this._a);
  void bar() {}
}

main() {
  HashSet hs = new HashSet();
  for (int i = 0; i < 1000; ++i) {
    hs.add(new Foo(i).bar);
  }

  var watch = new Stopwatch()..start();

  for (int i = 0; i < 1000; ++i) {
    for (var c in hs) {
      hs.contains(c);
    }
  }

  int time = watch.elapsedMilliseconds;
  print("Time: ${time}ms\n");
}

-------------------------------------
==========

to

==========
Reapply "Improve hashCode for closure objects" with fixes.

This CL includes the following fixes:
* Fix for incorrect non-nullable assumption about _Closure._hash field.
* Add error handling into BecomeMapTraits::Hash.
* Correct assertions for validating layout of Closure objects.
* Add identityHashCode to the list of VM entry points in precompiler.

Closes #30211.

Original code review:

https://codereview.chromium.org/2983823002/

Original CL description:

This performance improvement is inspired by Flutter listeners stored in
the HashSet (see ObserverList) and frequently checked using
HashSet.contains(). If there are many such listeners and they are
implicit instance closures (for example, created by
'new Listenable.merge(...)'), HashSet.contains() becomes very slow.
It spends a lot of time in Closure_equals native method due to hash
collisions between closure objects with same function
but different receivers.

This CL improves hashCode() calculation for implicit instance closures
by mixing function hashcode with identity hashcode of the receiver.
For explicit closures and static implicit closures hashCode() is
improved by using identityHashCode() of a closure object.

Also, hashcode is calculated once and cached in each closure instance.
The size of a closure instance doesn't grow up because there was unused
word-size padding both on 32-bit and 64-bit architectures.

The execution time of the following micro-benchmark is reduced from
47665ms to 135ms on my Linux/x64 box.

-------------------------------------

import "dart:collection";

class Foo {
  int _a;
  Foo(this._a);
  void bar() {}
}

main() {
  HashSet hs = new HashSet();
  for (int i = 0; i < 1000; ++i) {
    hs.add(new Foo(i).bar);
  }

  var watch = new Stopwatch()..start();

  for (int i = 0; i < 1000; ++i) {
    for (var c in hs) {
      hs.contains(c);
    }
  }

  int time = watch.elapsedMilliseconds;
  print("Time: ${time}ms\n");
}

-------------------------------------

R=zra@google.com

Committed:
https://github.com/dart-lang/sdk/commit/203955bc48fdbd03b7b030c4e6dbcd20920201ec
==========

[alexmarkov, 2017-07-20 22:22:25]

Committed patchset #1 (id:1) manually as
203955bc48fdbd03b7b030c4e6dbcd20920201ec (presubmit successful).