Stephen Adams b3fbb59d60 [dart2js] Construct _SyncStarIterator outside of transformed code ...

In the old scheme, sync* generators would have an entry and a
body. The entry contained typed checks and the body had injected code
to call a 'factory' helper method to construct the _SyncStarIterable.
It was necessary to pass the element type to the body to be passed to
the factory.

    int foo(T a, T b) sync* {yield f(a); yield f(b);}

is compiled to something like

    foo(a, b) {
      T._as(a); T._as(b);
      return foo$body(a, b, type$.int);
    }
    foo$body(a, b, R) {
      return _syncStarFactory(function(){BODY}, R);
    }

When type checks were disabled (`-O3`), it was often possible to
generate a single function by merging these as there were no checks.

The new scheme keeps the entry and body separate, and constructs the
_SyncStarIterable in the entry:

    foo(a, b) {
      T._as(a); T._as(b);
      return _syncStarFactory(foo$body(a, b), type$.int);
    }
    foo$body(a, b) {
      return function(){BODY};
    }

This keeps the typed Dart 'level' distinct from the untyped JavaScript
level.

The new scheme is a bit more verbose but has the advantage that the
call to `_syncStarFactory` can be inlined and optimized.

Change-Id: I13802d9c9eefd9323841670d059b75a81569d6cb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/296140
Reviewed-by: Mayank Patke <fishythefish@google.com>
Commit-Queue: Stephen Adams <sra@google.com>

2023-04-20 00:38:10 +00:00

..

async_await_js_transform_test.dart

[dart2js] Construct _SyncStarIterator outside of transformed code

2023-04-20 00:38:10 +00:00