now nvptx allows extern "C" task void, which is emits a kernel that should (?) be callable by driver API from external code

module.cpp

@@ -733,11 +733,13 @@ Module::AddFunctionDeclaration(const std::string &name,
     if (storageClass == SC_EXTERN_C) {
         // Make sure the user hasn't supplied both an 'extern "C"' and a
         // 'task' qualifier with the function
+#if 0 /* NVPTX64::task_and_externC */
         if (functionType->isTask) {
             Error(pos, "\"task\" qualifier is illegal with C-linkage extern "
                   "function \"%s\".  Ignoring this function.", name.c_str());
             return;
         }
+#endif
 
         std::vector<Symbol *> funcs;
         symbolTable->LookupFunction(name.c_str(), &funcs);
@@ -795,7 +797,7 @@ Module::AddFunctionDeclaration(const std::string &name,
 #else // LLVM 3.1 and 3.3+
         function->addFnAttr(llvm::Attribute::AlwaysInline);
 #endif
-    if (functionType->isTask)
+    if (functionType->isTask && g->target->getISA() != Target::NVPTX64)
         // This also applies transitively to members I think?
 #if defined(LLVM_3_1)
         function->setDoesNotAlias(1, true);