Fix lower bound in JSLoadContext typer.

R=rossberg@chromium.org

Review URL: https://codereview.chromium.org/549133002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23777 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/compiler/typer.cc

@@ -485,8 +485,6 @@ Bounds Typer::Visitor::TypeJSInstanceOf(Node* node) {
 // JS context operators.
 
 Bounds Typer::Visitor::TypeJSLoadContext(Node* node) {
-// TODO(rossberg): Fix this once we actually use the lower bound anywhere.
-#if 0
   Bounds outer = OperandType(node, 0);
   DCHECK(outer.upper->Maybe(Type::Internal()));
   // TODO(rossberg): More precisely, instead of the above assertion, we should
@@ -509,7 +507,7 @@ Bounds Typer::Visitor::TypeJSLoadContext(Node* node) {
       if (context_type->IsConstant()) {
         context = Handle<Context>::cast(context_type->AsConstant()->Value());
       }
-    } else {
+    } else if (!context.is_null()) {
       context = handle(context.ToHandleChecked()->previous(), isolate());
     }
   }
@@ -521,9 +519,6 @@ Bounds Typer::Visitor::TypeJSLoadContext(Node* node) {
     Type* lower = TypeConstant(value);
     return Bounds(lower, Type::Any(zone()));
   }
-#else
-  return Bounds::Unbounded(zone());
-#endif
 }