[turbofan] Use FastCloneShallow[Array|Object]Stub if possible.

src/ast.h

Index: src/ast.h
diff --git a/src/ast.h b/src/ast.h
index 7040ff78350bcfdc524114752ca33e559b0f1199..1c78adb6aa0f1d87bca6d061249444d683b56cf9 100644
--- a/src/ast.h
+++ b/src/ast.h
@@ -1507,6 +1507,9 @@ class ObjectLiteral FINAL : public MaterializedLiteral {
   int ComputeFlags(bool disable_mementos = false) const {
     int flags = fast_elements() ? kFastElements : kNoFlags;
     flags |= has_function() ? kHasFunction : kNoFlags;
+    if (depth() == 1 && !has_elements() && !may_store_doubles()) {
+      flags |= kShallowProperties;

[mvstanton, 2015/04/21 12:59:14]

Could you also push this flag into
FullCodeGenerator::MustCreateObjectLiteralWithRuntime()?
(in src/full-codegen.cc)

There are three tests that can be eliminated with a look at this nice new
kShallowProperties flag.

[Michael Starzinger, 2015/04/21 13:48:36]

Done.

+    }
     if (disable_mementos) {
       flags |= kDisableMementos;
     }
@@ -1517,7 +1520,8 @@ class ObjectLiteral FINAL : public MaterializedLiteral {
     kNoFlags = 0,
     kFastElements = 1,
     kHasFunction = 1 << 1,
-    kDisableMementos = 1 << 2
+    kShallowProperties = 1 << 2,
+    kDisableMementos = 1 << 3
   };
 
   struct Accessors: public ZoneObject {