C++ PATCH for c++/65327 aka DR 1688 (volatile constexpr variables)

[Marek Polacek]

The PR points out DR 1688: volatile + constexpr is a valid combination.
This patch makes the compiler accept such a code.

There's a related problem:
constexpr volatile int a = 42;
constexpr int b = a;
the initialization of b should be rejected, but it is not.  My patch does
not address this issue though.

Bootstrapped/regtested on x86_64-linux, ok for trunk?  If so, should this be
backported to 4.8/4.9?

2015-03-16  Marek Polacek  <pola...@redhat.com>

        DR 1688
        PR c++/65327
        * decl.c (grokdeclarator): Allow volatile and constexpr together.

        * g++.dg/cpp0x/constexpr-object1.C: Change dg-error to dg-bogus.
        * g++.dg/cpp0x/pr65327.C: New test.

diff --git gcc/cp/decl.c gcc/cp/decl.c
index e35e484..cb0f11f 100644
--- gcc/cp/decl.c
+++ gcc/cp/decl.c
@@ -10134,8 +10134,9 @@ grokdeclarator (const cp_declarator *declarator,
      the object as `const'.  */
   if (constexpr_p && innermost_code != cdk_function)
     {
-      if (type_quals & TYPE_QUAL_VOLATILE)
-        error ("both %<volatile%> and %<constexpr%> cannot be used here");
+      /* DR1688 says that a `constexpr' specifier in combination with
+        `volatile' is valid.  */
+
       if (TREE_CODE (type) != REFERENCE_TYPE)
        {
          type_quals |= TYPE_QUAL_CONST;
diff --git gcc/testsuite/g++.dg/cpp0x/constexpr-object1.C 
gcc/testsuite/g++.dg/cpp0x/constexpr-object1.C
index 41afbe9..287c3ac 100644
--- gcc/testsuite/g++.dg/cpp0x/constexpr-object1.C
+++ gcc/testsuite/g++.dg/cpp0x/constexpr-object1.C
@@ -19,7 +19,7 @@ constexpr A1 a2; // { dg-error "uninitialized const" }
 
 const constexpr A1 a3 = A1();
 
-volatile constexpr A1 a4 = A1(); // { dg-error "both .volatile. and 
.constexpr. cannot" }
+volatile constexpr A1 a4 = A1(); // { dg-bogus "both .volatile. and 
.constexpr. cannot" }
 
 // error: on type declaration
 constexpr struct pixel
diff --git gcc/testsuite/g++.dg/cpp0x/pr65327.C 
gcc/testsuite/g++.dg/cpp0x/pr65327.C
index e69de29..c6cefab 100644
--- gcc/testsuite/g++.dg/cpp0x/pr65327.C
+++ gcc/testsuite/g++.dg/cpp0x/pr65327.C
@@ -0,0 +1,18 @@
+// PR c++/65327
+// { dg-do compile { target c++11 } }
+// DR1688 says that constexpr can be used together with volatile.
+
+constexpr volatile int i = 10;
+
+void
+foo ()
+{
+  constexpr volatile int j = 5;
+  static constexpr volatile int k = 5;
+}
+
+constexpr volatile int
+bar ()
+{
+  return i;
+}

        Marek