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/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp
index a76058c..3b1c5bf 100644
--- a/clang/lib/CodeGen/CGExprAgg.cpp
+++ b/clang/lib/CodeGen/CGExprAgg.cpp
@@ -1352,7 +1352,8 @@
   // (int*)0 - Null pointer expressions.
   if (const CastExpr *ICE = dyn_cast<CastExpr>(E))
     return ICE->getCastKind() == CK_NullToPointer &&
-        CGF.getTypes().isPointerZeroInitializable(E->getType());
+           CGF.getTypes().isPointerZeroInitializable(E->getType()) &&
+           !E->HasSideEffects(CGF.getContext());
   // '\0'
   if (const CharacterLiteral *CL = dyn_cast<CharacterLiteral>(E))
     return CL->getValue() == 0;