Add an assert to further check the invariant that a null pointer

corresponds to another argument being valid.

This makes it clear that the code is correct despite the PVS-Studio
report that a pointer might be dereferenced prior to being checked for
whether it is null. It likely is also enough for static analyzers to not
flag the code.

llvm-svn: 285982

clang/lib/Sema/SemaExprObjC.cpp

@@ -2539,6 +2539,10 @@ ExprResult Sema::BuildInstanceMessage(Expr *Receiver,
                                       SourceLocation RBracLoc,
                                       MultiExprArg ArgsIn,
                                       bool isImplicit) {
+  assert((Receiver || SuperLoc.isValid()) && "If the Receiver is null, the "
+                                             "SuperLoc must be valid so we can "
+                                             "use it instead.");
+
   // The location of the receiver.
   SourceLocation Loc = SuperLoc.isValid()? SuperLoc : Receiver->getLocStart();
   SourceRange RecRange =