PR23833, DR2140: an lvalue-to-rvalue conversion on a glvalue of type
nullptr_t does not access memory.

We now reuse CK_NullToPointer to represent a conversion from a glvalue
of type nullptr_t to a prvalue of nullptr_t where necessary.

This reinstates r363337, reverted in r363352.

llvm-svn: 363429
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index 267402d..c416753 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -2148,14 +2148,14 @@
 
   case CK_NullToPointer:
     if (MustVisitNullValue(E))
-      (void) Visit(E);
+      CGF.EmitIgnoredExpr(E);
 
     return CGF.CGM.getNullPointer(cast<llvm::PointerType>(ConvertType(DestTy)),
                               DestTy);
 
   case CK_NullToMemberPointer: {
     if (MustVisitNullValue(E))
-      (void) Visit(E);
+      CGF.EmitIgnoredExpr(E);
 
     const MemberPointerType *MPT = CE->getType()->getAs<MemberPointerType>();
     return CGF.CGM.getCXXABI().EmitNullMemberPointer(MPT);