[vm] Add (S)LEB128 encoding/decoding to BaseWriteStream.

Unlike cfc8e6de, this does _not_ replace the default variable length
encoding for {Read,Write}Streams, but insteads adds separate
{Read,Write}{S,}LEB128 methods to the appropriate classes. If we later
find the cause of the issues that led to the revert of cfc8e6de, it'll
be easy to switch over then.

Note that WriteLEB128 asserts that the value is non-negative if used
with a signed type (since negative values suggests that SLEB128 should
be used instead for minimal encoding).

Also removes the various other encoding and decoding methods for
(S)LEB128 across the codebase and changes those clients to use
{Read,Write}Streams instead.

Other cleanups:

* Various constant-related cleanups in datastream.h.

* Adds DART_FORCE_INLINE to ReadStream::ReadByte and uses it in the
  default variable length decoding methods for retrieving bytes
  from the stream instead of managing current_ by hand.

* Creates a canonical empty CompressedStackMaps instance and uses
  that instead of the null CompressedStackMaps instance in most cases.
  The only remaining (expected) use of the null CompressedStackMaps
  instance is for the global table in the object store when no global
  table exists (e.g., in JIT mode before any snapshotting).

* Moves CompressedStackMapsIterator from code_descriptors.h to an
  Iterator class within CompressedStackMaps in object.h (similar to
  PcDescriptors::Iterator), to limit friend declarations and because it
  conceptually makes more sense as part of CompressedStackMaps.

* Removed CompressedStackMaps::PayloadByte, since existing clients
  (CompressedStackMaps::Iterator, StackMapEntry in program_visitor.cc)
  are better served by just operating on the payload buffer directly
  (with appropriate NoSafepointScopes).

* WriteStreams no longer allocate their initial space on construction,
  but rather on the first write, so no allocation is performed by
  constructing a never-used WriteStream.

Cq-Include-Trybots: luci.dart.try:vm-kernel-precomp-linux-debug-x64-try,vm-kernel-precomp-linux-debug-simarm_x64-try,vm-kernel-precomp-mac-release-simarm64-try,vm-kernel-mac-debug-x64-try,vm-kernel-win-debug-x64-try,vm-kernel-win-debug-ia32-try,vm-kernel-precomp-win-release-x64-try,vm-kernel-ubsan-linux-release-x64-try,vm-kernel-tsan-linux-release-x64-try,vm-kernel-precomp-ubsan-linux-release-x64-try,vm-kernel-precomp-tsan-linux-release-x64-try,vm-kernel-precomp-msan-linux-release-x64-try,vm-kernel-precomp-asan-linux-release-x64-try,vm-kernel-msan-linux-release-x64-try,vm-kernel-asan-linux-release-x64-try
Change-Id: Ice63321abaa79157fbe9f230a864c8bba0e6dea9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/166421
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Commit-Queue: Tess Strickland <sstrickl@google.com>
20 files changed
tree: 5c5a27eaa3e2cbd1ce5225e290f6ea5aaf967c5e
  1. .dart_tool/
  2. .github/
  3. benchmarks/
  4. build/
  5. client/
  6. docs/
  7. pkg/
  8. runtime/
  9. samples/
  10. samples-dev/
  11. sdk/
  12. tests/
  13. third_party/
  14. tools/
  15. utils/
  16. .clang-format
  17. .gitattributes
  18. .gitconfig
  19. .gitignore
  20. .gn
  21. .mailmap
  22. .packages
  23. .style.yapf
  24. .vpython
  25. AUTHORS
  26. BUILD.gn
  27. CHANGELOG.md
  28. codereview.settings
  29. CONTRIBUTING.md
  30. DEPS
  31. LICENSE
  32. PATENT_GRANT
  33. PRESUBMIT.py
  34. README.dart-sdk
  35. README.md
  36. sdk_args.gni
  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, getting started, and more.

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

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.