[for-in] Sanitize for-in optimizations and fix bailout points.

src/full-codegen/x64/full-codegen-x64.cc

Index: src/full-codegen/x64/full-codegen-x64.cc
diff --git a/src/full-codegen/x64/full-codegen-x64.cc b/src/full-codegen/x64/full-codegen-x64.cc
index 6d3d1b435b1ea495dbd59c0aa2db422fa7b571c4..d08ec34329fc2c9acd3e5979a7fca72ddf92be09 100644
--- a/src/full-codegen/x64/full-codegen-x64.cc
+++ b/src/full-codegen/x64/full-codegen-x64.cc
@@ -990,24 +990,20 @@ void FullCodeGenerator::VisitForInStatement(ForInStatement* stmt) {
   ForIn loop_statement(this, stmt);
   increment_loop_depth();
 
-  // Get the object to enumerate over. If the object is null or undefined, skip
-  // over the loop.  See ECMA-262 version 5, section 12.6.4.
+  // Get the object to enumerate over.
   SetExpressionAsStatementPosition(stmt->enumerable());
   VisitForAccumulatorValue(stmt->enumerable());
-  __ CompareRoot(rax, Heap::kUndefinedValueRootIndex);
-  __ j(equal, &exit);
-  Register null_value = rdi;
-  __ LoadRoot(null_value, Heap::kNullValueRootIndex);
-  __ cmpp(rax, null_value);
-  __ j(equal, &exit);
 
-  PrepareForBailoutForId(stmt->PrepareId(), TOS_REG);
-
-  // Convert the object to a JS object.
+  // If the object is null or undefined, skip over the loop, otherwise convert
+  // it to a JS receiver.  See ECMA-262 version 5, section 12.6.4.
   Label convert, done_convert;
   __ JumpIfSmi(rax, &convert, Label::kNear);
   __ CmpObjectType(rax, FIRST_JS_RECEIVER_TYPE, rcx);
   __ j(above_equal, &done_convert, Label::kNear);
+  __ CompareRoot(rax, Heap::kNullValueRootIndex);
+  __ j(equal, &exit);
+  __ CompareRoot(rax, Heap::kUndefinedValueRootIndex);
+  __ j(equal, &exit);
   __ bind(&convert);
   ToObjectStub stub(isolate());
   __ CallStub(&stub);
@@ -1015,16 +1011,14 @@ void FullCodeGenerator::VisitForInStatement(ForInStatement* stmt) {
   PrepareForBailoutForId(stmt->ToObjectId(), TOS_REG);
   __ Push(rax);
 
-  // Check for proxies.
-  Label call_runtime;
-  __ CmpObjectType(rax, JS_PROXY_TYPE, rcx);
-  __ j(equal, &call_runtime);
-
   // Check cache validity in generated code. This is a fast case for
   // the JSObject::IsSimpleEnum cache validity checks. If we cannot
   // guarantee cache validity, call the runtime system to check cache
   // validity or get the property names in a fixed array.
-  __ CheckEnumCache(null_value, &call_runtime);
+  // Note: Proxies never have an enum cache, so will always take the
+  // slow path.
+  Label call_runtime;
+  __ CheckEnumCache(&call_runtime);
 
   // The enum cache is valid.  Load the map of the object being
   // iterated over and use the cache for the iteration.