As a first step towards fixing PR9641, add a CK_DynamicToNull cast kind which
represents a dynamic cast where we know that the result is always null.

For example:

struct A {
  virtual ~A();
};
struct B final : A { };
struct C { };

bool f(B* b) {
  return dynamic_cast<C*>(b);
}



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@129256 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/CGExprAgg.cpp b/lib/CodeGen/CGExprAgg.cpp
index 75e3a78..5e1ac3c 100644
--- a/lib/CodeGen/CGExprAgg.cpp
+++ b/lib/CodeGen/CGExprAgg.cpp
@@ -255,7 +255,10 @@
   }
 
   switch (E->getCastKind()) {
-  case CK_Dynamic: {
+  case CK_Dynamic:
+  case CK_DynamicToNull: {
+
+    // FIXME: Actually handle DynamicToNull here.
     assert(isa<CXXDynamicCastExpr>(E) && "CK_Dynamic without a dynamic_cast?");
     LValue LV = CGF.EmitCheckedLValue(E->getSubExpr());
     // FIXME: Do we also need to handle property references here?