PR c++/86608 - reading constexpr volatile variable.

	* constexpr.c (potential_constant_expression_1): Check want_rval
	instead of checking if we have a decl.
	* decl2.c (decl_maybe_constant_var_p): Don't consider volatile
	constexpr variables as maybe constant.

	* g++.dg/cpp0x/constexpr-volatile2.C: New test.
	* g++.dg/cpp0x/pr65327.C: Add dg-error.

From-SVN: r267030

gcc/cp/ChangeLog

+2018-12-11  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/86608 - reading constexpr volatile variable.
+	* constexpr.c (potential_constant_expression_1): Check want_rval
+	instead of checking if we have a decl.
+	* decl2.c (decl_maybe_constant_var_p): Don't consider volatile
+	constexpr variables as maybe constant.
+
 2018-12-11  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	* decl.c (grokvardecl): Add location_t parameter and use it

gcc/cp/constexpr.c

@@ -5476,10 +5476,11 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
        available, so we don't bother with switch tracking.  */
     return true;
 
-  if (TREE_THIS_VOLATILE (t) && !DECL_P (t))
+  if (TREE_THIS_VOLATILE (t) && want_rval)
     {
       if (flags & tf_error)
-        error_at (loc, "expression %qE has side-effects", t);
+	error_at (loc, "lvalue-to-rvalue conversion of a volatile lvalue "
+		  "%qE with type %qT", t, TREE_TYPE (t));
       return false;
     }
   if (CONSTANT_CLASS_P (t))

gcc/cp/decl2.c

@@ -4313,7 +4313,7 @@ decl_maybe_constant_var_p (tree decl)
   tree type = TREE_TYPE (decl);
   if (!VAR_P (decl))
     return false;
-  if (DECL_DECLARED_CONSTEXPR_P (decl))
+  if (DECL_DECLARED_CONSTEXPR_P (decl) && !TREE_THIS_VOLATILE (decl))
     return true;
   if (DECL_HAS_VALUE_EXPR_P (decl))
     /* A proxy isn't constant.  */

gcc/testsuite/ChangeLog

+2018-12-11  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/86608 - reading constexpr volatile variable.
+	* g++.dg/cpp0x/constexpr-volatile2.C: New test.
+	* g++.dg/cpp0x/pr65327.C: Add dg-error.
+
 2018-12-11  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	* g++.dg/pr53037-4.C: Test the first two locations too.

gcc/testsuite/g++.dg/cpp0x/constexpr-volatile2.C

+// PR c++/86608
+// { dg-do compile { target c++11 } }
+
+template<typename T, T v> struct X {};
+
+int
+main ()
+{
+  static constexpr volatile int a = 3;
+  constexpr volatile int b = 2;
+  return (sizeof(X<decltype(a), a>) // { dg-error "lvalue-to-rvalue conversion of a volatile lvalue" }
+	  + sizeof(X<decltype(b), b>)); // { dg-error "lvalue-to-rvalue conversion of a volatile lvalue" }
+}

gcc/testsuite/g++.dg/cpp0x/pr65327.C

@@ -15,4 +15,4 @@ constexpr volatile int
 bar ()
 {
   return i;
-}
+} // { dg-error "lvalue-to-rvalue conversion of a volatile lvalue" }