commit 37d8c78237e875355ffe36d6b2b33c29606a43fa
author Mark Zhou <markzipan@google.com> Sat Dec 05 02:21:43 2020 +0000
committer commit-bot@chromium.org <commit-bot@chromium.org> Sat Dec 05 02:21:43 2020 +0000
tree 284d65d333c0879bf0fd744cd2dc8eca8190cb8f
parent 2448fc70b7a0038b8381cae9bd875750731a5e34

[dartdevc] Containerizing top-level variables to improve stepping times.

This change selectively containerizes many top-level JS constructs. Containers maintain a max size of 500 elements for JS optimization purposes. Containers with unspecified key names are emitted as JS arrays. Containerization occurs for symbols when the number of top level symbols exceeds 600 but is automatic for other constructs. However, containerization in the Dart SDK only happens for web libraries for runtime optimization purposes.

Two types of common DDC constructs result in their capture by all subsequent closures:
* Self-referential variables:
    var selfLambda = () => selfLambda = "foo";
* Variables referenced in sister functions:
    var unused = "foo";
    function unusedF() => console.log(unused);

The following are now accessed through an additional level of indirection:
* Type generators (frequently follow the self-referential variable pattern)
* Constant cache variables
* Dart private names (used for virtual method dispatch)
* Top-level string constants (such as URI strings)

Additional changes:
* The ModuleItemContainer handles automatic renaming of arbitrary top-level JS expressions. This is a multimap that maps keys of an arbitrary type to JS key-value pairs.
* The CacheTable and TypeTable have been unified. The old cache table seemed to have been created with a similar use case as the ModuleItemContainer but had become too specialized.
* The new TypeTable unifies much of the logic for emitting types, including explicitly separating the discharge of types dependent on free variables (such as generic types, generic functions, and their bounds) from types that are fully bound.

Reduces top-level captured variables in the SDK by ~5711 per recursive callback.

Change-Id: Id44efef8e93d1a83fdac808814d9ace99c4d27bd
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/173800
Commit-Queue: Mark Zhou <markzipan@google.com>
Reviewed-by: Anna Gringauze <annagrin@google.com>
Reviewed-by: Nicholas Shahan <nshahan@google.com>