[parser] Fix async generator bytecode to only await on explicit return

Per ECMA-262 25.5.3.2, step 5.e: |generatorBody| execution ends with a normal completion.

Bug: v8:9050
Change-Id: If2ecc7d104e0b905a4b2b4695522be740e0d0349
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1611011Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Joshua Litt <joshualitt@google.com>
Cr-Commit-Position: refs/heads/master@{#61589}

src/parsing/parser.cc

@@ -1717,7 +1717,7 @@ void Parser::ParseAndRewriteAsyncGeneratorFunctionBody(
   // try {
   //   InitialYield;
   //   ...body...;
-  //   return undefined; // See comment below
+  //   // fall through to the implicit return after the try-finally
   // } catch (.catch) {
   //   %AsyncGeneratorReject(generator, .catch);
   // } finally {
@@ -1744,12 +1744,6 @@ void Parser::ParseAndRewriteAsyncGeneratorFunctionBody(
 
     // Don't create iterator result for async generators, as the resume methods
     // will create it.
-    // TODO(leszeks): This will create another suspend point, which is
-    // unnecessary if there is already an unconditional return in the body.
-    Statement* final_return = BuildReturnStatement(
-        factory()->NewUndefinedLiteral(kNoSourcePosition), kNoSourcePosition);
-    statements.Add(final_return);
-
     try_block = factory()->NewBlock(false, statements);
   }
 

test/test262/test262.status

@@ -524,9 +524,6 @@
   # https://bugs.chromium.org/p/v8/issues/detail?id=9049
   'language/comments/hashbang/use-strict': [SKIP],
 
-  # https://bugs.chromium.org/p/v8/issues/detail?id=9050
-  'language/statements/async-generator/return-undefined-implicit-and-explicit': [FAIL],
-
   # https://bugs.chromium.org/p/v8/issues/detail?id=9228
   'built-ins/Proxy/defineProperty/targetdesc-not-configurable-writable-desc-not-writable': [FAIL],
   'built-ins/Proxy/deleteProperty/targetdesc-is-configurable-target-is-not-extensible': [FAIL],