%X => %_X, %_X => %__X

src/parser.cc

Index: src/parser.cc
diff --git a/src/parser.cc b/src/parser.cc
index 29b1fe74c6058a344f12d75e5d9407f0b86d1ae6..722e374f72a4f1554172ce4ed24d2e25b61d8229 100644
--- a/src/parser.cc
+++ b/src/parser.cc
@@ -4627,7 +4627,7 @@ Expression* Parser::ParseV8Intrinsic(bool* ok) {
       function->function_id == Runtime::kIS_VAR) {
     // %IS_VAR(x) evaluates to x if x is a variable,
     // leads to a parse error otherwise.  Could be implemented as an
-    // inline function %_IS_VAR(x) to eliminate this special case.
+    // inline function %__IS_VAR(x) to eliminate this special case.
     if (args->length() == 1 && args->at(0)->AsVariableProxy() != NULL) {
       return args->at(0);
     } else {
@@ -4646,11 +4646,16 @@ Expression* Parser::ParseV8Intrinsic(bool* ok) {
     return NULL;
   }
 
-  // Check that the function is defined if it's an inline runtime call.
-  if (function == NULL && name->Get(0) == '_') {
-    ReportMessage("not_defined", Vector<Handle<String> >(&name, 1));
-    *ok = false;
-    return NULL;
+  if (function == NULL && name->length() > 0 && name->Get(0) == '_') {
+    // Check that the function is defined if it's an inline runtime call.
+    if (name->length() > 1 && name->Get(1) == '_') {
+      ReportMessage("not_defined", Vector<Handle<String> >(&name, 1));
+      *ok = false;
+      return NULL;
+    }
+    // Assume this is a runtime-js function called via %_name.
+    name = isolate()->factory()->NewSubString(name, 1, name->length());
+    name = isolate()->factory()->LookupSymbol(name);
   }
 
   // We have a valid intrinsics call or a call to a builtin.