[ORC] fix use-after-free detected by -Wreturn-stack-address

[mgehre]

Summary

llvm/lib/ExecutionEngine/Orc/Layer.cpp:53:12: warning: returning address of local temporary object [-Wreturn-stack-address]

In

StringRef IRMaterializationUnit::getName() const {
[...]
     return TSM.withModuleDo(
        [](const Module &M) { return M.getModuleIdentifier(); });

getModuleIdentifier() returns a const std::string &, but the implicit return type
of the lambda is std::string by value, and thus the returned StringRef refers
to a temporary std::string.

Detect by annotating llvm::StringRef with [[gsl::Pointer]].

[lhames]

LGTM. Nice catch!

llvm/trunk/lib/ExecutionEngine/Orc/Layer.cpp

IRMaterializationUnit::IRMaterializationUnit(
     ThreadSafeModule TSM, VModuleKey K, SymbolFlagsMap SymbolFlags,
     SymbolNameToDefinitionMap SymbolToDefinition)
     : MaterializationUnit(std::move(SymbolFlags), std::move(K)),
       TSM(std::move(TSM)), SymbolToDefinition(std::move(SymbolToDefinition)) {}
 
 StringRef IRMaterializationUnit::getName() const {
   if (TSM)
     return TSM.withModuleDo(
-        [](const Module &M) { return M.getModuleIdentifier(); });
+        [](const Module &M) -> StringRef { return M.getModuleIdentifier(); });
   return "<null module>";
 }
 
 void IRMaterializationUnit::discard(const JITDylib &JD,
                                     const SymbolStringPtr &Name) {
   LLVM_DEBUG(JD.getExecutionSession().runSessionLocked([&]() {
     dbgs() << "In " << JD.getName() << " discarding " << *Name << " from MU@"
            << this << " (" << getName() << ")\n";