Merge 2018-11 CWG Motion 9

P1327R1 Allowing dynamic_cast, polymorphic typeid in Constant Expressions

Fixes #2401

Author: zygoloid

source/expressions.tex

@@ -6626,9 +6626,6 @@
 \item
 a conversion from type \cv{}~\tcode{void*} to a pointer-to-object type;
 
-\item
-a dynamic cast\iref{expr.dynamic.cast};
-
 \item
 a \tcode{reinterpret_cast}\iref{expr.reinterpret.cast};
 
@@ -6642,10 +6639,6 @@
 that refers to a non-volatile object
 whose lifetime began within the evaluation of \tcode{e};
 
-\item
-a typeid expression\iref{expr.typeid} whose operand is a glvalue of a
-polymorphic class type;
-
 \item
 a \grammarterm{new-expression}\iref{expr.new};
 
@@ -6662,7 +6655,9 @@
 operator where the result is unspecified;
 
 \item
-a \grammarterm{throw-expression}\iref{expr.throw}; or
+a \grammarterm{throw-expression}\iref{expr.throw} or
+a dynamic cast\iref{expr.dynamic.cast} or \tcode{typeid}\iref{expr.typeid} expression
+that would throw an exception; or
 
 \item
 an invocation of the \tcode{va_arg} macro\iref{cstdarg.syn}.