Add basic crankshaft support for slow-mode for-in to avoid disabling optimizations

src/hydrogen.cc

Index: src/hydrogen.cc
diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index d6cbc1444ad52eac67ab0f98ecd35f3a8e3943ae..cf4c87f02e70a73b57b6a0edeb72e687bb3311aa 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -5050,10 +5050,6 @@ void HOptimizedGraphBuilder::VisitForInStatement(ForInStatement* stmt) {
     return Bailout(kForInStatementOptimizationIsDisabled);
   }
 
-  if (stmt->for_in_type() != ForInStatement::FAST_FOR_IN) {
-    return Bailout(kForInStatementIsNotFastCase);
-  }
-
   if (!stmt->each()->IsVariableProxy() ||
       !stmt->each()->AsVariableProxy()->var()->IsStackLocal()) {
     return Bailout(kForInStatementWithNonLocalEachVariable);
@@ -5064,13 +5060,42 @@ void HOptimizedGraphBuilder::VisitForInStatement(ForInStatement* stmt) {
   CHECK_ALIVE(VisitForValue(stmt->enumerable()));
   HValue* enumerable = Top();  // Leave enumerable at the top.
 
-  HInstruction* map = Add<HForInPrepareMap>(enumerable);
-  Add<HSimulate>(stmt->PrepareId());
-
-  HInstruction* array = Add<HForInCacheArray>(
-      enumerable, map, DescriptorArray::kEnumCacheBridgeCacheIndex);
+  HInstruction* map;
+  HInstruction* array;
+  HInstruction* enum_length;
+  bool fast = stmt->for_in_type() == ForInStatement::FAST_FOR_IN;
+  if (fast) {
+    map = Add<HForInPrepareMap>(enumerable);
+    Add<HSimulate>(stmt->PrepareId());
+
+    array = Add<HForInCacheArray>(enumerable, map,
+                                  DescriptorArray::kEnumCacheBridgeCacheIndex);
+    enum_length = Add<HMapEnumLength>(map);
+
+    HInstruction* index_cache = Add<HForInCacheArray>(
+        enumerable, map, DescriptorArray::kEnumCacheBridgeIndicesCacheIndex);
+    HForInCacheArray::cast(array)
+        ->set_index_cache(HForInCacheArray::cast(index_cache));
+  } else {
+    Add<HSimulate>(stmt->PrepareId());
+    {
+      NoObservableSideEffectsScope no_effects(this);
+      BuildJSObjectCheck(enumerable, 0);
+    }
+    Add<HSimulate>(stmt->ToObjectId());
 
-  HInstruction* enum_length = Add<HMapEnumLength>(map);
+    map = graph()->GetConstant1();
+    Runtime::FunctionId function_id = Runtime::kGetPropertyNamesFast;
+    Add<HPushArguments>(enumerable);
+    array = Add<HCallRuntime>(isolate()->factory()->empty_string(),
+                              Runtime::FunctionForId(function_id), 1);
+    Push(array);
+    Add<HSimulate>(stmt->EnumId());
+    Drop(1);
+    Handle<Map> array_map = isolate()->factory()->fixed_array_map();
+    HValue* check = Add<HCheckMaps>(array, array_map);
+    enum_length = AddLoadFixedArrayLength(array, check);
+  }
 
   HInstruction* start_index = Add<HConstant>(0);
 
@@ -5079,13 +5104,9 @@ void HOptimizedGraphBuilder::VisitForInStatement(ForInStatement* stmt) {
   Push(enum_length);
   Push(start_index);
 
-  HInstruction* index_cache = Add<HForInCacheArray>(
-      enumerable, map, DescriptorArray::kEnumCacheBridgeIndicesCacheIndex);
-  HForInCacheArray::cast(array)->set_index_cache(
-      HForInCacheArray::cast(index_cache));
-
   HBasicBlock* loop_entry = BuildLoopEntry(stmt);
 
+  enumerable = environment()->ExpressionStackAt(4);

[mvstanton, 2015/04/10 11:40:07]

nit: why do you need to get enumerable again? Add a comment about that.

   HValue* index = environment()->ExpressionStackAt(0);
   HValue* limit = environment()->ExpressionStackAt(1);
 
@@ -5107,18 +5128,23 @@ void HOptimizedGraphBuilder::VisitForInStatement(ForInStatement* stmt) {
 
   set_current_block(loop_body);
 
-  HValue* key = Add<HLoadKeyed>(
-      environment()->ExpressionStackAt(2),  // Enum cache.
-      environment()->ExpressionStackAt(0),  // Iteration index.
-      environment()->ExpressionStackAt(0),
-      FAST_ELEMENTS);
+  HValue* key =
+      Add<HLoadKeyed>(environment()->ExpressionStackAt(2),  // Enum cache.
+                      index, index, FAST_ELEMENTS);
 
-  // Check if the expected map still matches that of the enumerable.
-  // If not just deoptimize.
-  Add<HCheckMapValue>(environment()->ExpressionStackAt(4),
-                      environment()->ExpressionStackAt(3));
-
-  Bind(each_var, key);
+  if (fast) {
+    // Check if the expected map still matches that of the enumerable.
+    // If not just deoptimize.
+    Add<HCheckMapValue>(enumerable, environment()->ExpressionStackAt(3));
+    Bind(each_var, key);
+  } else {
+    HValue* function = AddLoadJSBuiltin(Builtins::FILTER_KEY);
+    Add<HPushArguments>(enumerable, key);
+    key = Add<HInvokeFunction>(function, 2);
+    Bind(each_var, key);
+    Add<HSimulate>(stmt->AssignmentId());
+    Add<HCheckHeapObject>(key);
+  }
 
   BreakAndContinueInfo break_info(stmt, scope(), 5);
   {