commit 2cfa1726ad59ed34e2d87b2dafe2f60f775233e3
author Martin Kustermann <kustermann@google.com> Mon Jul 08 09:52:24 2024 +0000
committer Commit Queue <dart-scoped@luci-project-accounts.iam.gserviceaccount.com> Mon Jul 08 09:52:24 2024 +0000
tree 6e763b8e014078cbd4c8205c147ee619e468a307
parent 164c10a1502f9adf21c27ecf4c69c15bcad73968

[dart2wasm] Extend specialized is/as helper functions for non-instantiated types

The specialized is/as checker functions are currently only used
for cases where the type to check against doesn't require checking
argument types.

This CL will extend that for cases where we do have to check
argument types, but we know that there's no need to substitute
type arguments. This saves the RTT system from searching for
the type argument substitution value.

Cases where this applies is for example
```
class Base<T> {}
class Sub<T> extends Base<T> {}
class Sub2<T> extends Base<T> {}
class Sub3<T> extends Base<T> {}

final l = <Base<Object>>[Sub<int>(), Sub2<String>(), Sub3<double>()];
foo<T>() {
  final Base<Object> b = l[1];
  if (b is Base<T>) { ... }
  if (b is Base<String>) { ... }
}
```

Here we know that all classes that directly or indirectly implement
`Base<T>` just pass their type parameter up the hierarchy.
=> There's no need to translate from type parameter array of subclass
to that of the super class.

We'll generate optimized is/as helpers for this case now, e.g.
```
func foo {
      ...
      local.get $var0
      global.get $global40
      call $<obj> is Base<T0>
      ...
}

func $<obj> is Base<T0> {
      // Check whether obj is in class-id range of Base subtypes
      i32.const 0
      local.get $var0
      struct.get $Base $field0
      i32.const 107
      i32.sub
      i32.const 3
      i32.ge_u
      br_if $label0
      drop
      // Call Object._getTypeArguments()
      i32.const 0
      local.get $var0
      local.get $var0
      struct.get $Base $field0
      i32.const 338
      i32.add
      call_indirect (param (ref $#Top)) (result (ref $Array<_Type>))
      // Check whether first type argument is subtype of T0
      i32.const 0
      array.get $Array<_Type>
      ref.null none
      local.get $var1
      ref.null none
      call $_TypeUniverse.isSubtype
      i32.const 1
      i32.ne
      br_if $label0
      drop
      i32.const 1
}
```

It has overall negligible code size impact (~ 0.1% increase)

Issue https://github.com/dart-lang/sdk/issues/55516

Change-Id: Ic151269ad1b4a1456782b387beb4d646786ac493
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/374681
Reviewed-by: Ömer Ağacan <omersa@google.com>
Commit-Queue: Martin Kustermann <kustermann@google.com>