[llvm] Add assertions for the smart pointers with the possibility to be null in ModuleLazyLoaderCache::operator()

[OikawaKirie]

Summary

Split from D91844.

The return value of function ModuleLazyLoaderCache::operator() in file llvm/tools/llvm-link/llvm-link.cpp. According to the bug report of my static analyzer, the std::function variable ModuleLazyLoaderCache::createLazyModule points to function loadFile, which may return nullptr when error. And the pointer is dereferenced without a check.

[tejohnson]

lgtm

[OikawaKirie]

If the revision is done, please commit it on my behalf. Thank you.

Ella Ma <[e-mail]>

llvm/tools/llvm-link/llvm-link.cpp

std::unique_ptr<Module> takeModule(const std::string &FileName) {
     return Ret;
   }
 };
 
 // Get a Module for \p FileName from the cache, or load it lazily.
 Module &ModuleLazyLoaderCache::operator()(const char *argv0,
                                           const std::string &Identifier) {
   auto &Module = ModuleMap[Identifier];
-  if (!Module)
+  if (!Module) {
     Module = createLazyModule(argv0, Identifier);
+    assert(Module && "Failed to create lazy module!");
+  }
   return *Module;
 }
 } // anonymous namespace
 
 namespace {
 struct LLVMLinkDiagnosticHandler : public DiagnosticHandler {
   bool handleDiagnostics(const DiagnosticInfo &DI) override {
     unsigned Severity = DI.getSeverity();