HLoadNamedField for Smis optimized for x64

R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/108633003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@18283 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen-instructions.h

@@ -6216,7 +6216,11 @@ class HLoadNamedField V8_FINAL : public HTemplateInstruction<1> {
       set_representation(Representation::Integer32());
     } else if (representation.IsSmi()) {
       set_type(HType::Smi());
-      set_representation(representation);
+      if (SmiValuesAre32Bits()) {
+        set_representation(Representation::Integer32());
+      } else {
+        set_representation(representation);
+      }
     } else if (representation.IsDouble() ||
                representation.IsExternal() ||
                representation.IsInteger32()) {

src/x64/lithium-codegen-x64.cc

@@ -2843,7 +2843,17 @@ void LCodeGen::DoLoadNamedField(LLoadNamedField* instr) {
     __ movq(result, FieldOperand(object, JSObject::kPropertiesOffset));
     object = result;
   }
-  __ Load(result, FieldOperand(object, offset), access.representation());
+
+  Representation representation = access.representation();
+  if (representation.IsSmi() &&
+      instr->hydrogen()->representation().IsInteger32()) {
+    // Read int value directly from upper half of the smi.
+    STATIC_ASSERT(kSmiTag == 0);
+    STATIC_ASSERT(kSmiTagSize + kSmiShiftSize == 32);
+    offset += kPointerSize / 2;
+    representation = Representation::Integer32();
+  }
+  __ Load(result, FieldOperand(object, offset), representation);
 }