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

1 files changed, 4 insertions, 2 deletions

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 7b3590aeb1a..9b1e362c262 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -635,8 +635,10 @@ ExprResult Sema::DefaultLvalueConversion(Expr *E) {
   if (E->getType().getObjCLifetime() == Qualifiers::OCL_Weak)
     Cleanup.setExprNeedsCleanups(true);
 
-  Res = ImplicitCastExpr::Create(Context, T, CK_LValueToRValue, E, nullptr,
-                                 VK_RValue);
+  // C++ [conv.lval]p3:
+  //   If T is cv std::nullptr_t, the result is a null pointer constant.
+  CastKind CK = T->isNullPtrType() ? CK_NullToPointer : CK_LValueToRValue;
+  Res = ImplicitCastExpr::Create(Context, T, CK, E, nullptr, VK_RValue);
 
   // C11 6.3.2.1p2:
   //   ... if the lvalue has atomic type, the value has the non-atomic version