C++ PATCH for c++/85679 and CWG 2094 - volatile scalars are trivially copyable

[Marek Polacek]

CWG 2094 partially reverts CWG 496, which means that volatile-qualified scalars
are, once again, trivially copyable; [basic.types] now says "Scalar types,
trivially copyable class types, arrays of such types, and cv-qualified
versions of these types are collectively called trivially copyable types."

This previously changed in c++/63959 and this patch pretty much just reverts it.

I'm CCing libstdc++ because a test in libstdc++ needed updating.

Links to aforementioned CWGs:
<http://wg21.link/cwg496>
<http://wg21.link/cwg2094>

Bootstrapped/regtested on x86_64-linux, ok for trunk?  Not planning to backport
this.

2019-05-19  Marek Polacek  <polacek@redhat.com>

	CWG 2094 - volatile scalars are trivially copyable.
	PR c++/85679
	* tree.c (trivially_copyable_p): Don't check CP_TYPE_VOLATILE_P for
	scalar types.

	* g++.dg/ext/is_trivially_constructible1.C: Change the expected result
	for volatile int.
	* g++.dg/ext/is_trivially_copyable.C: New test.

	* testsuite/20_util/is_trivially_copyable/value.cc: Change the expected
	result for volatile int.

diff --git gcc/gcc/cp/tree.c gcc/gcc/cp/tree.c
index 8d7f7a2c3e7..821f2b79a67 100644
--- gcc/gcc/cp/tree.c
+++ gcc/gcc/cp/tree.c
@@ -4098,7 +4098,8 @@ trivially_copyable_p (const_tree t)
 	    && !TYPE_HAS_COMPLEX_MOVE_ASSIGN (t)
 	    && TYPE_HAS_TRIVIAL_DESTRUCTOR (t));
   else
-    return !CP_TYPE_VOLATILE_P (t) && scalarish_type_p (t);
+    /* CWG 2094 makes volatile-qualified scalars trivially copyable.  */
+    return scalarish_type_p (t);
 }
 
 /* Returns 1 iff type T is a trivial type, as defined in [basic.types] and
diff --git gcc/gcc/testsuite/g++.dg/ext/is_trivially_constructible1.C gcc/gcc/testsuite/g++.dg/ext/is_trivially_constructible1.C
index 191b69601e6..d28f2f7b24e 100644
--- gcc/gcc/testsuite/g++.dg/ext/is_trivially_constructible1.C
+++ gcc/gcc/testsuite/g++.dg/ext/is_trivially_constructible1.C
@@ -48,7 +48,9 @@ SA(!__is_trivially_constructible(int*, const int*));
 SA(!__is_trivially_constructible(D));
 
 SA(__is_trivially_copyable(int));
-SA(!__is_trivially_copyable(volatile int));
+// Changed in CWG 2094, which made volatile-qualified scalars trivially
+// copyable.
+SA(__is_trivially_copyable(volatile int));
 
 struct E1 {const int val;};
 SA(__is_trivially_copyable(E1));
diff --git gcc/gcc/testsuite/g++.dg/ext/is_trivially_copyable.C gcc/gcc/testsuite/g++.dg/ext/is_trivially_copyable.C
new file mode 100644
index 00000000000..6f93602c8c2
--- /dev/null
+++ gcc/gcc/testsuite/g++.dg/ext/is_trivially_copyable.C
@@ -0,0 +1,16 @@
+// CWG 2094 - volatile scalars are trivially copyable.
+// PR c++/85679
+// { dg-do compile { target c++11 } }
+
+#define SA(X) static_assert((X),#X)
+
+struct S{};
+
+SA(__is_trivially_copyable(S volatile));
+SA(__is_trivially_copyable(S volatile[]));
+SA(__is_trivially_copyable(S const volatile));
+SA(__is_trivially_copyable(S const volatile[]));
+SA(__is_trivially_copyable(int volatile));
+SA(__is_trivially_copyable(int volatile[]));
+SA(__is_trivially_copyable(int const volatile));
+SA(__is_trivially_copyable(int const volatile[]));
diff --git gcc/libstdc++-v3/testsuite/20_util/is_trivially_copyable/value.cc gcc/libstdc++-v3/testsuite/20_util/is_trivially_copyable/value.cc
index cce620daf4d..022f0c0b248 100644
--- gcc/libstdc++-v3/testsuite/20_util/is_trivially_copyable/value.cc
+++ gcc/libstdc++-v3/testsuite/20_util/is_trivially_copyable/value.cc
@@ -46,8 +46,10 @@ void test01()
 
   static_assert(test_property<is_trivially_copyable, 
 		int>(true), "");
+  // Changed in CWG 2094, which made volatile-qualified scalars trivially
+  // copyable.
   static_assert(test_property<is_trivially_copyable,
-		volatile int>(false), "");
+		volatile int>(true), "");
   static_assert(test_property<is_trivially_copyable, 
 		TType>(true), "");
   static_assert(test_property<is_trivially_copyable,