Add support for profile-based startup optimizations.

Add support for profile-based startup optimizations.

An experimental (and undocumented) flag '--experimental-track-allocations' makes the '--fast-startup' compiler add instructions that track which classes are allocated.

By going to the JavaScript console and dumping this information as JSON into `allocated_classes_profile` the next dart2js compilation can optimize the startup by deferring the initialization of the classes that weren't necessary for startup.

The workflow would look something like:
```
dart2js --fast-startup --experimental-track-allocations -o foo.js -o foo.dart
// Run the program in Chrome and run the following command in the console:
JSON.stringify($__dart_deferred_initializers__.allocations)
// Take the result and copy it into a file, say "allocations.json".
// Then rerun the compilation with the allocation-information.
dart2js --experimental-allocations-path=allocations.json --fast-startup -o foo.js -o foo.dart
```

R=sra@google.com

Committed: https://github.com/dart-lang/sdk/commit/237313b0279c36e247f147e722d0c3f38e38f6fa

[floitsch, 2017-04-29 01:31:37]

Description was changed from

==========
Add support for profile-based startup optimizations.

An experimental (and undocumented) flag '--track-allocations' makes the
'--fast-startup' compiler add instructions that track which classes are
allocated.

By going to the JavaScript console and dumping this information as JSON
into `allocated_classes_profile` the next dart2js compilation can optimize
the startup by deferring the initialization of the classes that weren't
necessary for startup.

The workflow would look something like:
```
dart2js --fast-startup --track-allocations -o foo.js -o foo.dart
// Run the program in Chrome and run the following command in the console:
JSON.stringify($__dart_deferred_initializers__.allocations)
// Take the result and copy it into a file, or hardcode it into
// `compiler/lib/src/js_emitter_program_builder/allocated_classes_profile.dart`
//
// Then rerun the compilation with the allocation-information.
dart2js --fast-startup -o foo.js -o foo.dart
// If the allocation-info is in a file, use the following command instead:
DART_VM_OPTIONS='-Ddart2js.allocatedClasses=allocations.json' dart2js
--fast-startup -o foo.js -o foo.dart
```
==========

to

==========
Add support for profile-based startup optimizations.

An experimental (and undocumented) flag '--track-allocations' makes the
'--fast-startup' compiler add instructions that track which classes are
allocated.

By going to the JavaScript console and dumping this information as JSON into
`allocated_classes_profile` the next dart2js compilation can optimize the
startup by deferring the initialization of the classes that weren't necessary
for startup.

The workflow would look something like:
```
dart2js --fast-startup --track-allocations -o foo.js -o foo.dart
// Run the program in Chrome and run the following command in the console:
JSON.stringify($__dart_deferred_initializers__.allocations)
// Take the result and copy it into a file, or hardcode it into
// `compiler/lib/src/js_emitter_program_builder/allocated_classes_profile.dart`
//
// Then rerun the compilation with the allocation-information.
dart2js --fast-startup -o foo.js -o foo.dart
// If the allocation-info is in a file, use the following command instead:
DART_VM_OPTIONS='-Ddart2js.allocatedClasses=allocations.json' dart2js
--fast-startup -o foo.js -o foo.dart
```
==========

[floitsch, 2017-04-29 01:36:31]

floitsch@google.com changed reviewers:
+ sigmund@google.com, sra@google.com

[floitsch, 2017-04-29 01:36:32]

Initial experiments were very promising.
I would like to continue some tests with Greentea / Adwords-Next.
Having the code committed inside dart2js would simplify that.
If the tests don't work out, it should be easy to revert this CL.

[sra1, 2017-05-02 20:40:13]

LGTM

I don't like having half-baked code in the compiler, so can you make it more
obvious?

1. Create a tracking issue xxx.
2. Put TODO(xxx) in all the places where stuff is mysterious or half-baked.
3. Consider calling more things 'experimentalXXX', like the option , field and
methods.

The TODOs will be useful in the cleanup for production quality if the idea tests
out well.

https://codereview.chromium.org/2847343002/diff/20001/pkg/compiler/lib/src/js...
File
pkg/compiler/lib/src/js_emitter/program_builder/allocated_classes_profile.dart
(right):

https://codereview.chromium.org/2847343002/diff/20001/pkg/compiler/lib/src/js...
pkg/compiler/lib/src/js_emitter/program_builder/allocated_classes_profile.dart:7:
const String allocatedClassesJson = null;
It is not clear what the purpose of this is.

https://codereview.chromium.org/2847343002/diff/20001/pkg/compiler/lib/src/js...
File pkg/compiler/lib/src/js_emitter/program_builder/program_builder.dart
(right):

https://codereview.chromium.org/2847343002/diff/20001/pkg/compiler/lib/src/js...
pkg/compiler/lib/src/js_emitter/program_builder/program_builder.dart:79: const
String.fromEnvironment("dart2js.allocatedClasses");
Can you make this a command-line option?

https://codereview.chromium.org/2847343002/diff/20001/pkg/compiler/lib/src/js...
pkg/compiler/lib/src/js_emitter/program_builder/program_builder.dart:599:
(allocatedClassesPath != null || allocatedClassesJson != null)) {
Does this execute once?
Perhaps make it more clear by putting some code in a helper init method.

https://codereview.chromium.org/2847343002/diff/20001/pkg/compiler/lib/src/js...
File pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart
(right):

https://codereview.chromium.org/2847343002/diff/20001/pkg/compiler/lib/src/js...
pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart:324:
o.__proto__ = o.constructor.prototype;
This will make Firefox angry.

[floitsch, 2017-05-06 19:25:44]

PTAL.
I didn't name everything to "experimental". When things were called
"softDeferred" (or similar) I kept them as is.
The code is still quite small, so I don't think we will have difficulties
reverting it, if the experiment doesn't work out.

Also made it easier to use. Will update the CL description to explain how to use
it now.

https://codereview.chromium.org/2847343002/diff/20001/pkg/compiler/lib/src/js...
File
pkg/compiler/lib/src/js_emitter/program_builder/allocated_classes_profile.dart
(right):

https://codereview.chromium.org/2847343002/diff/20001/pkg/compiler/lib/src/js...
pkg/compiler/lib/src/js_emitter/program_builder/allocated_classes_profile.dart:7:
const String allocatedClassesJson = null;
On 2017/05/02 20:40:12, sra1 wrote:
> It is not clear what the purpose of this is.

It was supposed to make it easier for Google3 to provide the profile-run data.
In retrospect that was probably never the case.
Removed.

https://codereview.chromium.org/2847343002/diff/20001/pkg/compiler/lib/src/js...
File pkg/compiler/lib/src/js_emitter/program_builder/program_builder.dart
(right):

https://codereview.chromium.org/2847343002/diff/20001/pkg/compiler/lib/src/js...
pkg/compiler/lib/src/js_emitter/program_builder/program_builder.dart:79: const
String.fromEnvironment("dart2js.allocatedClasses");
On 2017/05/02 20:40:12, sra1 wrote:
> Can you make this a command-line option?

done.

https://codereview.chromium.org/2847343002/diff/20001/pkg/compiler/lib/src/js...
pkg/compiler/lib/src/js_emitter/program_builder/program_builder.dart:599:
(allocatedClassesPath != null || allocatedClassesJson != null)) {
On 2017/05/02 20:40:13, sra1 wrote:
> Does this execute once?
> Perhaps make it more clear by putting some code in a helper init method.

done.

https://codereview.chromium.org/2847343002/diff/20001/pkg/compiler/lib/src/js...
File pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart
(right):

https://codereview.chromium.org/2847343002/diff/20001/pkg/compiler/lib/src/js...
pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart:324:
o.__proto__ = o.constructor.prototype;
On 2017/05/02 20:40:13, sra1 wrote:
> This will make Firefox angry.

Yes. I added a comment.

[floitsch, 2017-05-06 19:27:12]

Description was changed from

==========
Add support for profile-based startup optimizations.

An experimental (and undocumented) flag '--track-allocations' makes the
'--fast-startup' compiler add instructions that track which classes are
allocated.

By going to the JavaScript console and dumping this information as JSON into
`allocated_classes_profile` the next dart2js compilation can optimize the
startup by deferring the initialization of the classes that weren't necessary
for startup.

The workflow would look something like:
```
dart2js --fast-startup --track-allocations -o foo.js -o foo.dart
// Run the program in Chrome and run the following command in the console:
JSON.stringify($__dart_deferred_initializers__.allocations)
// Take the result and copy it into a file, or hardcode it into
// `compiler/lib/src/js_emitter_program_builder/allocated_classes_profile.dart`
//
// Then rerun the compilation with the allocation-information.
dart2js --fast-startup -o foo.js -o foo.dart
// If the allocation-info is in a file, use the following command instead:
DART_VM_OPTIONS='-Ddart2js.allocatedClasses=allocations.json' dart2js
--fast-startup -o foo.js -o foo.dart
```
==========

to

==========
Add support for profile-based startup optimizations.

An experimental (and undocumented) flag '--experimental-track-allocations' makes
the '--fast-startup' compiler add instructions that track which classes are
allocated.

By going to the JavaScript console and dumping this information as JSON into
`allocated_classes_profile` the next dart2js compilation can optimize the
startup by deferring the initialization of the classes that weren't necessary
for startup.

The workflow would look something like:
```
dart2js --fast-startup --experimental-track-allocations -o foo.js -o foo.dart
// Run the program in Chrome and run the following command in the console:
JSON.stringify($__dart_deferred_initializers__.allocations)
// Take the result and copy it into a file, say "allocations.json".
// Then rerun the compilation with the allocation-information.
dart2js --experimental-allocations-path=allocations.json --fast-startup -o
foo.js -o foo.dart
```
==========

[sra1, 2017-05-09 17:31:02]

lgtm

[floitsch, 2017-05-09 18:33:35]

Description was changed from

==========
Add support for profile-based startup optimizations.

An experimental (and undocumented) flag '--experimental-track-allocations' makes
the '--fast-startup' compiler add instructions that track which classes are
allocated.

By going to the JavaScript console and dumping this information as JSON into
`allocated_classes_profile` the next dart2js compilation can optimize the
startup by deferring the initialization of the classes that weren't necessary
for startup.

The workflow would look something like:
```
dart2js --fast-startup --experimental-track-allocations -o foo.js -o foo.dart
// Run the program in Chrome and run the following command in the console:
JSON.stringify($__dart_deferred_initializers__.allocations)
// Take the result and copy it into a file, say "allocations.json".
// Then rerun the compilation with the allocation-information.
dart2js --experimental-allocations-path=allocations.json --fast-startup -o
foo.js -o foo.dart
```
==========

to

==========
Add support for profile-based startup optimizations.

An experimental (and undocumented) flag '--experimental-track-allocations' makes
the '--fast-startup' compiler add instructions that track which classes are
allocated.

By going to the JavaScript console and dumping this information as JSON into
`allocated_classes_profile` the next dart2js compilation can optimize the
startup by deferring the initialization of the classes that weren't necessary
for startup.

The workflow would look something like:
```
dart2js --fast-startup --experimental-track-allocations -o foo.js -o foo.dart
// Run the program in Chrome and run the following command in the console:
JSON.stringify($__dart_deferred_initializers__.allocations)
// Take the result and copy it into a file, say "allocations.json".
// Then rerun the compilation with the allocation-information.
dart2js --experimental-allocations-path=allocations.json --fast-startup -o
foo.js -o foo.dart
```

R=sra@google.com

Committed:
https://github.com/dart-lang/sdk/commit/237313b0279c36e247f147e722d0c3f38e38f6fa
==========

[floitsch, 2017-05-09 18:33:36]

Committed patchset #4 (id:60001) manually as
237313b0279c36e247f147e722d0c3f38e38f6fa (presubmit successful).