commit 5a4b252252f6955dd1b418ad85d48af251da6ce9
author Jess Lally <jessicalally@google.com> Thu Sep 07 09:52:57 2023 +0000
committer Commit Queue <dart-scoped@luci-project-accounts.iam.gserviceaccount.com> Thu Sep 07 09:52:57 2023 +0000
tree abadc60e08b0aa314e38deacd89d999fcf85d725
parent 2bbf99351e0274643b8ab0c14904efbb650ded8b

[dart2wasm] Replace `struct.new_default` with `struct.new` for object
allocation.

When using the `struct.new_default` instruction for object allocation,
fields are always nullable and mutable. By using the `struct.new`
instruction instead, class fields can now have the same mutability and
nullability in Wasm as declared in Dart. In addition, the class ID and
type parameters (which are also stored in an object's struct), can now
be immutable and nonnullable as well.

To do this, object construction is now split into three functions:
(1) Initializer: evaluates initializers for instance fields and
constructor initializers (this constructor before super constructor).
(2) Constructor body: executes the constructor body (super constructor
before this constructor), with `this` pointed to the constructed object.
(3) Constructor allocator: which calls (1), allocates the object using
`struct.new`, then calls (2).

Because fields now have the correct mutability and nullability in Wasm,
this removes unnecessary null checks for nonnullable fields, and may
allow for better optimisations by Binaryen.

Fixes https://github.com/dart-lang/sdk/issues/51492

Change-Id: Ib26046686f772a70509a870301217e9b1c91b77e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/315820
Commit-Queue: Jess Lally <jessicalally@google.com>
Reviewed-by: Aske Simon Christensen <askesc@google.com>