[turbofan] Fix two bugs in ReduceArrayIteratorPrototypeNext

- Add missing uses of MapInference::NoChange.
- Insert map checks even if inferred maps were reliable, because
  they were inferred for an earlier effect input.

Bug: chromium:958420, chromium:958350, v8:9197
Change-Id: Id7677b1fc6f1e09dc12ae178f1155e4245b4e3e6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1593077
Auto-Submit: Georg Neis <neis@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61157}

src/compiler/js-call-reducer.cc

@@ -4921,6 +4921,7 @@ Reduction JSCallReducer::ReduceArrayIteratorPrototypeNext(Node* node) {
       CreateArrayIteratorParametersOf(iterator->op()).kind();
   Node* iterated_object = NodeProperties::GetValueInput(iterator, 0);
   Node* iterator_effect = NodeProperties::GetEffectInput(iterator);
+
   MapInference inference(broker(), iterated_object, iterator_effect);
   if (!inference.HaveMaps()) return inference.NoChange();
   MapHandles const& iterated_object_maps = inference.GetMaps();
@@ -4932,26 +4933,28 @@ Reduction JSCallReducer::ReduceArrayIteratorPrototypeNext(Node* node) {
     // TurboFan doesn't support loading from BigInt typed arrays yet.
     if (elements_kind == BIGUINT64_ELEMENTS ||
         elements_kind == BIGINT64_ELEMENTS) {
-      return NoChange();
+      return inference.NoChange();
     }
     for (Handle<Map> map : iterated_object_maps) {
       MapRef iterated_object_map(broker(), map);
       if (iterated_object_map.elements_kind() != elements_kind) {
-        return NoChange();
+        return inference.NoChange();
       }
     }
   } else {
     if (!CanInlineArrayIteratingBuiltin(broker(), iterated_object_maps,
                                         &elements_kind)) {
-      return NoChange();
+      return inference.NoChange();
     }
   }
 
   if (IsHoleyElementsKind(elements_kind)) {
     if (!dependencies()->DependOnNoElementsProtector()) UNREACHABLE();
   }
-  inference.RelyOnMapsPreferStability(dependencies(), jsgraph(), &effect,
-                                      control, p.feedback());
+  // Since the map inference was done relative to {iterator_effect} rather than
+  // {effect}, we need to guard the use of the map(s) even when the inference
+  // was reliable.
+  inference.InsertMapChecks(jsgraph(), &effect, control, p.feedback());
 
   if (IsFixedTypedArrayElementsKind(elements_kind)) {
     // See if we can skip the detaching check.

test/mjsunit/compiler/regress-958350.js

+// Copyright 2019 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --allow-natives-syntax
+
+function foo(o) {
+  for (const x of o) {
+    o[100] = 1;
+    try { x.push(); } catch (e) {}
+  }
+}
+
+foo([1]);
+foo([1]);
+%OptimizeFunctionOnNextCall(foo);
+foo([1]);

test/mjsunit/compiler/regress-958420.js

+// Copyright 2019 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --allow-natives-syntax
+
+var a = [];
+
+function foo() {
+  return a[Symbol.iterator]().next();
+}
+
+a.__proto__.push(5);
+a.bla = {};
+
+foo();
+%OptimizeFunctionOnNextCall(foo);
+foo();