This is a reland of commit 135443706b
Original change's description:
> [vm] Avoid expanding/flattening type arguments vectors in Type objects
>
> Previously, vectors of type arguments were expanded to include type
> arguments corresponding to superclasses both in the instances of
> generic classes and in Type objects (after type finalization).
> As a result, Type objects after finalization could be recursive and
> need to use extra TypeRef objects to break loops. The finalization of
> types was very complex and sometimes slow.
>
> This change simplifies the representation of Type objects: now they
> always have short type argument vectors, corresponding only to
> the type parameters of their own classes (both before and after
> finalization). Vectors of type arguments in the instances of generic
> classes are still expanded/flattened.
>
> This greatly simplifies type finalization, makes Type objects
> non-recursive and removes the need to create and handle excessive
> TypeRefs for type arguments corresponding to superclasses,
> as those type arguments are no longer included into types.
> The only remaining use of TypeRefs is for bounds of type parameters.
>
> In order to expand/flatten type arguments, new methods Type::GetInstanceTypeArguments / Class::GetInstanceTypeArguments
> are introduced. They build canonical declaration type arguments
> once (for each class), and then instantiate them as needed.
>
> There are also simple helper methods to shrink type arguments (TypeArguments::FromInstanceTypeArguments) and expand type arguments without filling type arguments corresponding to superclasses (TypeArguments::ToInstantiatorTypeArguments).
>
> Time of edge case 'regress_51960_test' 15min -> 300ms.
>
> TEST=ci, runtime/tests/vm/dart/regress_51960_test.dart
>
> Fixes https://github.com/dart-lang/sdk/issues/52022
> Fixes https://github.com/dart-lang/sdk/issues/51960
>
> Change-Id: I75b466b74698a33c0bb5e1dcbd29542e413812a1
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/295060
> Reviewed-by: Ryan Macnak <rmacnak@google.com>
> Commit-Queue: Alexander Markov <alexmarkov@google.com>
TEST=runtime/tests/vm/dart/regress_b_278841863_test.dart
Fixes b/278841863.
Change-Id: Ib1e20055bfb26e1df0a077300c69f0bec7152480
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/296300
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Commit-Queue: Alexander Markov <alexmarkov@google.com>
Alexander Markov
7247a1b3b7