[dart2wasm] Implement inlining functions with function expressions in the body

[osa1]

Consider this function from the protobuf library:

void _readPacked(CodedBufferReader input, void Function() readFunc) {
  input._withLimit(input.readInt32(), () {
    while (!input.isAtEnd()) {
      readFunc();
    }
  });
}

Assuming wasm-opt can inline and eliminate dart2wasm closures with just one call site, inlining this can potentially yield performance improvements, as it would eliminate tear-off allocations in the call sites.

Doing the same transformation manually yielded great improvements: google/protobuf.dart#911.

However we currently can't do this, because function expressions currently prevent inlining:

sdk/pkg/dart2wasm/lib/translator.dart

Line 954 in 94e653f

if (membersContainingInnerFunctions.contains(member)) return false;

We should remove this restriction and allow inlining functions with function expressions.

[osa1]

I wasn't sure what is missing here and what needs to be done, so I've run the tests (with optimizations) with the membersContainingInnerFunctions line removed.

These are the failing tests:

• language/optimize/inferrer_synthesized_super_constructor_test
• language/constructor/evaluation_redirecting_constructor_test
• language/type_variable/field_initializer_closure_test
• language/super/call2_test
• language/regress/regress25246_1_test
• language/type_variable/field_initializer_closure2_test
• language/variance/variance_out_field_test
• language/constructor/constructor6_test
• language/variance/variance_in_field_test
• language/variance/variance_inout_field_test
• lib/js/export/static_interop_mock/mockito_test

They all fail with the same error:

[parse exception: Reached function end without seeing End opcode (at 0:97305)]
Fatal: error parsing wasm (try --debug for more info)

A small repro:

class A {
  @pragma("wasm:prefer-inline")
  Function foo = (int x) {};
}

class B extends A {
  void m(int x) {
    foo(x);
  }
}

main() {
  var b = B();
  b.m(123);
}

It looks like the function to the closure is missing an end. wami output looks like this:

128319|  (func $_TypeUniverse.substituteFunctionTypeArgument (;850;) (param $var0 (ref $_FunctionType)) (param $var1 (ref $Array<_Type>)) (result (ref $_FunctionType))
...
128354|  )
128356|  (func $A. closure at file:///usr/local/google/home/omersa/dart/sdk_wasm/test/test.dart:2:18 (;851;) (param $var0 (ref struct)) (param $var1 i64) (result noneref)
128358|  (func $new B (initializer) (;852;) (result (ref $#ClosureBase))
...
128392|  )

Note that the closing paranthesis is missing for $A. closure at ....

(Minor: we should probably drop the . in the closure name: $A closure at ...)