clang/Modules: Bring back optimization lost in 31e14f41a21f

31e14f41a21f9016050a20f07d5da03db2e8c13e accidentally dropped caching of
failed module loads.  This brings it back by making
ModuleMap::getCachedModuleLoad return an Optional.

1 files changed, 4 insertions, 3 deletions

diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index cc3d848c1e0..a0663217453 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -1633,10 +1633,11 @@ CompilerInstance::loadModule(SourceLocation ImportLoc,
   }
 
   // If we don't already have information on this module, load the module now.
+  Module *Module = nullptr;
   ModuleMap &MM = getPreprocessor().getHeaderSearchInfo().getModuleMap();
-  clang::Module *Module = MM.getCachedModuleLoad(*Path[0].first);
-  if (Module) {
-    // Nothing to do here, we found it.
+  if (auto MaybeModule = MM.getCachedModuleLoad(*Path[0].first)) {
+    // Use the cached result, which may be nullptr.
+    Module = *MaybeModule;
   } else if (ModuleName == getLangOpts().CurrentModule) {
     // This is the module we're building.
     Module = PP->getHeaderSearchInfo().lookupModule(