[dart2wasm] Use vm's modular transformers as-optimization lowering

Currently `-O4` drops explicit as-checks. Before changing this, we have
to do more optimizations on type checks. As a start, we call out to the
VM's lowering of as-checks in the modular transformer.

Issue #55516

Change-Id: I71f35a95ab41cc7a30f7dea088d9d41ac5243f59
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/365141
Commit-Queue: Martin Kustermann <[email protected]>
Reviewed-by: Slava Egorov <[email protected]>

Author: mkustermann

pkg/dart2wasm/lib/transformers.dart

@@ -8,6 +8,8 @@ import 'package:kernel/core_types.dart';
 import 'package:kernel/target/targets.dart';
 import 'package:kernel/type_algebra.dart';
 import 'package:kernel/type_environment.dart';
+import 'package:vm/modular/transformations/type_casts_optimizer.dart'
+    as typeCastsOptimizer show transformAsExpression;
 
 import 'list_factory_specializer.dart';
 
@@ -704,6 +706,12 @@ class _WasmTransformer extends Transformer {
     node.transformChildren(this);
     return node.receiver;
   }
+
+  @override
+  TreeNode visitAsExpression(AsExpression node) {
+    node.transformChildren(this);
+    return typeCastsOptimizer.transformAsExpression(node, typeContext);
+  }
 }
 
 class _AsyncStarFrame {

pkg/front_end/testcases/dart2wasm/inference_update_2/issue52452.dart.strong.transformed.expect

@@ -128,13 +128,13 @@ static method testConflictWithNoSuchMethodForwarderIfImplementedInMixin(self::C
 }
 static method testNoConflictWithNoSuchMethodForwarderIfImplementedInMixin1(self::C c) → void {
   if(!(c.{self::C::_f3}{core::int?} == null)) {
-    core::int x = c.{self::C::_f3}{core::int?} as{Unchecked} core::int;
+    core::int x = let core::int? #t3 = c.{self::C::_f3}{core::int?} in #t3 == null ?{core::int} #t3 as{Unchecked} core::int : #t3{core::int};
     self::acceptsInt(x);
   }
 }
 static method testNoConflictWithNoSuchMethodForwarderIfImplementedInMixin2(self::C c) → void {
   if(!(c.{self::C::_f4}{core::int?} == null)) {
-    core::int x = c.{self::C::_f4}{core::int?} as{Unchecked} core::int;
+    core::int x = let core::int? #t4 = c.{self::C::_f4}{core::int?} in #t4 == null ?{core::int} #t4 as{Unchecked} core::int : #t4{core::int};
     self::acceptsInt(x);
   }
 }