dart2js: inlining difference in dart2

[sigmundch]

This example shows _checkLength gets inlined in Dart1 but not in Dart2. The _checkLength function simply returns the parameter and has no checks, even in compliance mode.

import 'dart:typed_data';

const C = 304;

main() {
  print(new Uint8List(0));
  print(new Uint8List(C));
}

[vsmenon]

@rakudrama - is this something that should be fixed before dart2stable?

[rakudrama]

int _checkLength(length) {
  if (length is! int) throw new ArgumentError('Invalid length $length');
  return length;
}

The Dart 1 code simply returns length

static method _checkLength(dynamic length) → dart.core::int {
  if(!(length is dart.core::int))
    throw new dart.core::ArgumentError::•("Invalid length ${length}");
  return length;
}

Type inference for negative tests did not make it into Dart 2.0, so the Dart 2 code has an implicit cast:

static method _checkLength(dynamic length) → dart.core::int {
  if(!(length is dart.core::int))
    throw new dart.core::ArgumentError::•("Invalid length ${length}");
  return length as{TypeError} dart.core::int;
}

The extra nodes for the cast make the function look too big to inline.

Type inference should be improved as much as possible, since this kind of consequence is widespread in user code (#32236).

Meantime, I will experiment with rewriting _checkLength to fit into the current constrains of type inference and the inliner.

[rakudrama]

https://dart-review.googlesource.com/c/sdk/+/58542 fixes this instance.