SILOptimizer: avoid use-after-free with the name

On Windows at least, the std::string associated with the name of the
property would be copy constructed before being passed to the diagnostic
engine.  The resultant DiagnosticArgument in the InFlightDiagnostic
would hold a StringRef to the copy-constructed std::string.  However,
because the arguments are inalloca'ed on Windows, the copy constructed
string would be destructed before the return of the argument.
Fortunately, this would result in the standard library overwriting the
string and the use-after-free would fail to print the argument.
Explicitly construct the StringRef before passing the name to the
diagnostic to avoid the use-after-free.

Author: compnerd

lib/SILOptimizer/Mandatory/DefiniteInitialization.cpp

@@ -650,7 +650,8 @@ void LifetimeChecker::noteUninitializedMembers(const DIMemoryUse &Use) {
     if (Decl && !Decl->isImplicit())
       Loc = SILLocation(Decl);
 
-    diagnose(Module, Loc, diag::stored_property_not_initialized, Name);
+    diagnose(Module, Loc, diag::stored_property_not_initialized,
+             StringRef(Name));
   }
 }
 
@@ -707,7 +708,7 @@ void LifetimeChecker::diagnoseInitError(const DIMemoryUse &Use,
   for (unsigned i = 0, e = Use.NumElements; i != e; ++i)
     isLet &= TheMemory.isElementLetProperty(i);
 
-  diagnose(Module, DiagLoc, DiagMessage, Name, isLet);
+  diagnose(Module, DiagLoc, DiagMessage, StringRef(Name), isLet);
 
   // As a debugging hack, print the instruction itself if there is no location
   // information.  This should never happen.
@@ -1164,10 +1165,10 @@ void LifetimeChecker::handleInOutUse(const DIMemoryUse &Use) {
                FD->getName(), /*method*/ 0, PropertyName);
     } else if (isAssignment) {
       diagnose(Module, Use.Inst->getLoc(),
-               diag::assignment_to_immutable_value, PropertyName);
+               diag::assignment_to_immutable_value, StringRef(PropertyName));
     } else {
       diagnose(Module, Use.Inst->getLoc(),
-               diag::immutable_value_passed_inout, PropertyName);
+               diag::immutable_value_passed_inout, StringRef(PropertyName));
     }
 
     if (auto *Var = dyn_cast<VarDecl>(VD)) {