Replace tagged keys for fast access by smi, and use smi in boundscheck.

src/code-stubs-hydrogen.cc

Index: src/code-stubs-hydrogen.cc
diff --git a/src/code-stubs-hydrogen.cc b/src/code-stubs-hydrogen.cc
index 14bd8f9c9439afe5512ecce4526d14c5e5c0a4b1..cbd1c95daacbc32092a0249cee41b9f15c4390d3 100644
--- a/src/code-stubs-hydrogen.cc
+++ b/src/code-stubs-hydrogen.cc
@@ -418,7 +418,7 @@ HValue* CodeStubGraphBuilder<KeyedLoadFastElementStub>::BuildCodeStub() {
   HInstruction* load = BuildUncheckedMonomorphicElementAccess(
       GetParameter(0), GetParameter(1), NULL, NULL,
       casted_stub()->is_js_array(), casted_stub()->elements_kind(),
-      false, NEVER_RETURN_HOLE, STANDARD_STORE, Representation::Tagged());
+      false, NEVER_RETURN_HOLE, STANDARD_STORE, Representation::Smi());
   return load;
 }
 
@@ -464,7 +464,7 @@ HValue* CodeStubGraphBuilder<KeyedStoreFastElementStub>::BuildCodeStub() {
       GetParameter(0), GetParameter(1), GetParameter(2), NULL,
       casted_stub()->is_js_array(), casted_stub()->elements_kind(),
       true, NEVER_RETURN_HOLE, casted_stub()->store_mode(),
-      Representation::Tagged());
+      Representation::Smi());
 
   return GetParameter(2);
 }
@@ -588,11 +588,9 @@ HValue* CodeStubGraphBuilder<ArraySingleArgumentConstructorStub>::
       new(zone()) HConstant(initial_capacity, Representation::Tagged());
   AddInstruction(initial_capacity_node);
 
-  // Since we're forcing Integer32 representation for this HBoundsCheck,
-  // there's no need to Smi-check the index.
   HBoundsCheck* checked_arg = AddBoundsCheck(argument, max_alloc_length,
                                              ALLOW_SMI_KEY,
-                                             Representation::Tagged());
+                                             Representation::Smi());
   IfBuilder if_builder(this);
   if_builder.IfCompare(checked_arg, constant_zero, Token::EQ);
   if_builder.Then();