[turbofan] Simplify graph construction for for-in.

src/compiler/ast-graph-builder.cc

 // Copyright 2014 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.
 
 #include "src/compiler/ast-graph-builder.h"
 
 #include "src/compiler.h"
 #include "src/compiler/ast-loop-assignment-analyzer.h"
 #include "src/compiler/control-builders.h"
 #include "src/compiler/js-type-feedback.h"
@@ skipping 1310 matching lines @@
     //                a few simplified instructions.
     Node* cache_pair = NewNode(
         javascript()->CallRuntime(Runtime::kForInInit, 2), obj, cache_type);
     // cache_type may have been replaced.
     Node* cache_array = NewNode(common()->Projection(0), cache_pair);
     cache_type = NewNode(common()->Projection(1), cache_pair);
     Node* cache_length =
         NewNode(javascript()->CallRuntime(Runtime::kForInCacheArrayLength, 2),
                 cache_type, cache_array);
     {
-      // TODO(dcarney): this check is actually supposed to be for the
-      //                empty enum case only.
-      IfBuilder have_no_properties(this);
-      Node* empty_array_cond = NewNode(javascript()->StrictEqual(),
-                                       cache_length, jsgraph()->ZeroConstant());
-      have_no_properties.If(empty_array_cond);
-      have_no_properties.Then();
-      // Pop obj and skip loop.
-      environment()->Pop();
-      have_no_properties.Else();
-      {
-        // Construct the rest of the environment.
-        environment()->Push(cache_type);
-        environment()->Push(cache_array);
-        environment()->Push(cache_length);
-        environment()->Push(jsgraph()->ZeroConstant());
+      // Construct the rest of the environment.
+      environment()->Push(cache_type);
+      environment()->Push(cache_array);
+      environment()->Push(cache_length);
+      environment()->Push(jsgraph()->ZeroConstant());
 
-        // Build the actual loop body.
-        VisitForInBody(stmt);
-      }
-      have_no_properties.End();
+      // Build the actual loop body.
+      VisitForInBody(stmt);
     }
     is_null.End();
   }
   is_undefined.End();
 }
 
 
 // TODO(dcarney): this is a big function.  Try to clean up some.
 void AstGraphBuilder::VisitForInBody(ForInStatement* stmt) {
   LoopBuilder for_loop(this);
@@ skipping 2434 matching lines @@
     // Phi does not exist yet, introduce one.
     value = NewPhi(inputs, value, control);
     value->ReplaceInput(inputs - 1, other);
   }
   return value;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8