PR44958: Allow member calls and typeid / dynamic_cast on mutable objects

and objects with mutable subobjects.

The standard wording doesn't really cover these cases; accepting all
such cases seems most in line with what we do in other cases and what
other compilers do. (Essentially this means we're assuming that objects
external to the evaluation are always in-lifetime.)

1 files changed, 7 insertions, 0 deletions

diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index dfa9444..641368e 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -3140,6 +3140,13 @@ struct CompleteObject {
       : Base(Base), Value(Value), Type(Type) {}
 
   bool mayAccessMutableMembers(EvalInfo &Info, AccessKinds AK) const {
+    // If this isn't a "real" access (eg, if it's just accessing the type
+    // info), allow it. We assume the type doesn't change dynamically for
+    // subobjects of constexpr objects (even though we'd hit UB here if it
+    // did). FIXME: Is this right?
+    if (!isAnyAccess(AK))
+      return true;
+
     // In C++14 onwards, it is permitted to read a mutable member whose
     // lifetime began within the evaluation.
     // FIXME: Should we also allow this in C++11?