SILOptimizer: fix a few instances of use-after-free

When building on Windows, the std::string being passed will on the
stack, where the destructor will be invoked before the return, nil'ing
out reference.  This causes incorrect behaviour when building the
diagnostic or FIXITs.  Explicitly create the StringRef to prevent the
std::string from being invalidated.

Author: compnerd

lib/SILOptimizer/Mandatory/DefiniteInitialization.cpp

@@ -929,12 +929,13 @@ void LifetimeChecker::handleStoreUse(unsigned UseID) {
       // a diagnostic.
       if (!shouldEmitError(Use.Inst))
         continue;
-      
+
       std::string PropertyName;
       auto *VD = TheMemory.getPathStringToElement(i, PropertyName);
       diagnose(Module, Use.Inst->getLoc(),
-               diag::immutable_property_already_initialized, PropertyName);
-      
+               diag::immutable_property_already_initialized,
+               StringRef(PropertyName));
+
       if (auto *Var = dyn_cast<VarDecl>(VD)) {
         if (Var->getParentInitializer())
           diagnose(Module, SILLocation(VD),
@@ -1089,7 +1090,7 @@ void LifetimeChecker::handleInOutUse(const DIMemoryUse &Use) {
 
     std::string PropertyName;
     auto VD = TheMemory.getPathStringToElement(i, PropertyName);
-    
+
     // Try to produce a specific error message about the inout use.  If this is
     // a call to a method or a mutating property access, indicate that.
     // Otherwise, we produce a generic error.
@@ -1154,15 +1155,15 @@ void LifetimeChecker::handleInOutUse(const DIMemoryUse &Use) {
                  : diag::using_mutating_accessor_on_immutable_value,
                accessor->getStorage()->getBaseName(),
                isa<SubscriptDecl>(accessor->getStorage()),
-               PropertyName);
+               StringRef(PropertyName));
     } else if (FD && FD->isOperator()) {
       diagnose(Module, Use.Inst->getLoc(),
                diag::mutating_method_called_on_immutable_value,
-               FD->getName(), /*operator*/ 1, PropertyName);
+               FD->getName(), /*operator*/ 1, StringRef(PropertyName));
     } else if (FD && isSelfParameter) {
       diagnose(Module, Use.Inst->getLoc(),
                diag::mutating_method_called_on_immutable_value,
-               FD->getName(), /*method*/ 0, PropertyName);
+               FD->getName(), /*method*/ 0, StringRef(PropertyName));
     } else if (isAssignment) {
       diagnose(Module, Use.Inst->getLoc(),
                diag::assignment_to_immutable_value, StringRef(PropertyName));