List all registered backends in case particular backend is not found (#…

…3088)

Summary:
Print all backends, improve debuggability in case particular backend is missing.

Documentation:
n/a
Pull Request resolved: #3088

Differential Revision: D15781780

Pulled By: rdzhabarov

fbshipit-source-id: 5edb63be413dfd934effafcda18f54b7aa41b9df

include/glow/Support/Register.h

@@ -62,7 +62,7 @@ template <class Key, class Base> class FactoryRegistry {
     return it->second->create();
   }
 
-private:
+  /// \returns all registered factories.
   static FactoryMap &factories() {
     static FactoryMap *factories = new FactoryMap();
     return *factories;

lib/Backends/Backends.cpp

@@ -25,6 +25,14 @@ Backend *createBackend(BackendKind backendKind) {
 
 Backend *createBackend(llvm::StringRef backendName) {
   auto *backend = FactoryRegistry<std::string, Backend>::get(backendName);
+
+  if (backend == nullptr) {
+    LOG(INFO) << "List of all registered backends:";
+    for (const auto &factory :
+         FactoryRegistry<std::string, Backend>::factories()) {
+      LOG(INFO) << factory.first;
+    }
+  }
   CHECK(backend) << strFormat("Cannot find registered backend: %s",
                               backendName.data());
   return backend;