[analyzer] Make Reference.children a "union type"

Reference.children is nullable in order to avoid having a lot of empty
maps. This is good.
What happens next is that it very often is a map with one entry in it
which is also wasteful.
This CL makes it a "union type" where it is either null (0 children),
a Reference (1 child) or a Map (2 or more children).

Testing this on the 82 contexts in flutter/flutter this reduces memory
consumption with about 200-250 MB.

Details:

_Uint32List instances:
Difference at 95.0% confidence
   -980946.67 +/- 7879.31
   -38.24% +/- 0.31%

_Map instances:
Difference at 95.0% confidence
   -984938.00 +/- 0.00
   -51.79% +/- 0.00%

_List instances:
Difference at 95.0% confidence
   -984961.33 +/- 125.34
   -16.23% +/- 0.00%

_Uint32List bytes:
Difference at 95.0% confidence
   -62803269.33 +/- 557111.00
   -11.96% +/- 0.11%

_Map bytes:
Difference at 95.0% confidence
   -63036032.00 +/- 0.00
   -51.79% +/- 0.00%

_List bytes:
Difference at 95.0% confidence
   -94588442.67 +/- 279618.85
   -11.35% +/- 0.03%

heapUsage:
Difference at 95.0% confidence
   -221706613.33 +/- 6459537.53
   -5.75% +/- 0.17%

currentRSS:
Difference at 95.0% confidence
   -265419434.67 +/- 102602928.35
   -5.64% +/- 2.18%

heapCapacity:
Difference at 95.0% confidence
   -266518528.00 +/- 108692904.34
   -6.56% +/- 2.67%
Change-Id: Id1018f5a3cd708654d171bec0ad8bf4d2525b002
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/319960
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Jens Johansen <jensj@google.com>
3 files changed
tree: 8a19f9033fc925ba9fcdb518e2daa07ff71a7835
  1. .dart_tool/
  2. .github/
  3. benchmarks/
  4. build/
  5. docs/
  6. pkg/
  7. runtime/
  8. samples/
  9. sdk/
  10. tests/
  11. third_party/
  12. tools/
  13. utils/
  14. .clang-format
  15. .gitattributes
  16. .gitconfig
  17. .gitignore
  18. .gn
  19. .mailmap
  20. .style.yapf
  21. .vpython
  22. AUTHORS
  23. BUILD.gn
  24. CHANGELOG.md
  25. codereview.settings
  26. CONTRIBUTING.md
  27. DEPS
  28. LICENSE
  29. OWNERS
  30. PATENT_GRANT
  31. PRESUBMIT.py
  32. README.dart-sdk
  33. README.md
  34. sdk.code-workspace
  35. sdk_args.gni
  36. SECURITY.md
  37. WATCHLISTS
README.md

Dart

A client-optimized language for fast apps on any platform

Dart is:

  • Optimized for UI: Develop with a programming language specialized around the needs of user interface creation.

  • Productive: Make changes iteratively: use hot reload to see the result instantly in your running app.

  • Fast on all platforms: Compile to ARM & x64 machine code for mobile, desktop, and backend. Or compile to JavaScript for the web.

Dart's flexible compiler technology lets you run Dart code in different ways, depending on your target platform and goals:

  • Dart Native: For programs targeting devices (mobile, desktop, server, and more), Dart Native includes both a Dart VM with JIT (just-in-time) compilation and an AOT (ahead-of-time) compiler for producing machine code.

  • Dart Web: For programs targeting the web, Dart Web includes both a development time compiler (dartdevc) and a production time compiler (dart2js).

Dart platforms illustration

License & patents

Dart is free and open source.

See LICENSE and PATENT_GRANT.

Using Dart

Visit dart.dev to learn more about the language, tools, and to find codelabs.

Browse pub.dev for more packages and libraries contributed by the community and the Dart team.

Our API reference documentation is published at api.dart.dev, based on the stable release. (We also publish docs from our beta and dev channels, as well as from the primary development branch).

Building Dart

If you want to build Dart yourself, here is a guide to getting the source, preparing your machine to build the SDK, and building.

There are more documents on our wiki.

Contributing to Dart

The easiest way to contribute to Dart is to file issues.

You can also contribute patches, as described in Contributing.