Rewrite enum_flags, add unit tests, fix problems

This patch started by adding comprehensive unit tests for enum_flags.

For the testing part, it adds:

 - tests of normal expected uses of the API.

 - checks that _invalid_ uses of the API would fail to compile.  I.e.,
   it validates that enum_flags really is a strong type, and that
   incorrect mixing of enum types would be caught at compile time.  It
   pulls that off making use of SFINEA and C++11's decltype/constexpr.

This revealed many holes in the enum_flags API.  For example, the f1
assignment below currently incorrectly fails to compile:

 enum_flags<flags> f1 = FLAG1;
 enum_flags<flags> f2 = FLAG2 | f1;

The unit tests also revealed that this useful use case doesn't work:

    enum flag { FLAG1 = 1, FLAG2 = 2 };
    enum_flags<flag> src = FLAG1;
    enum_flags<flag> f1 = condition ? src : FLAG2;

It fails to compile because enum_flags<flag> and flag are convertible
to each other.

Turns out that making enum_flags be implicitly convertible to the
backing raw enum type was not a good idea.

If we make it convertible to the underlying type instead, we fix that
ternary operator use case, and, we find cases throughout the codebase
that should be using the enum_flags but were using the raw backing
enum instead.  So it's a good change overall.

Also, several operators were missing.

These holes and more are plugged by this patch, by reworking how the
enum_flags operators are implemented, and making use of C++11's
feature of being able to delete methods/functions.

There are cases in gdb/compile/ where we need to call a function in a
C plugin API that expects the raw enum.  To address cases like that,
this adds a "raw()" method to enum_flags.  This way we can keep using
the safer enum_flags to construct the value, and then be explicit when
we need to get at the raw enum.

This makes most of the enum_flags operators constexpr.  Beyond
enabling more compiler optimizations and enabling the new unit tests,
this has other advantages, like making it possible to use operator|
with enum_flags values in switch cases, where only compile-time
constants are allowed:

    enum_flags<flags> f = FLAG1 | FLAG2;
    switch (f)
      {
      case FLAG1 | FLAG2:
	break;
      }

Currently that fails to compile.

It also switches to a different mechanism of enabling the global
operators.  The current mechanism isn't namespace friendly, the new
one is.

It also switches to C++11-style SFINAE -- instead of wrapping the
return type in a SFINAE-friently structure, we use an unnamed template
parameter.  I.e., this:

  template <typename enum_type,
	    typename = is_enum_flags_enum_type_t<enum_type>>
  enum_type
  operator& (enum_type e1, enum_type e2)

instead of:

  template <typename enum_type>
  typename enum_flags_type<enum_type>::type
  operator& (enum_type e1, enum_type e2)

Note that the static_assert inside operator~() was converted to a
couple overloads (signed vs unsigned), because static_assert is too
late for SFINAE-based tests, which is important for the CHECK_VALID
unit tests.

Tested with gcc {4.8, 7.1, 9.3} and clang {5.0.2, 10.0.0}.

gdb/ChangeLog:

	* Makefile.in (SELFTESTS_SRCS): Add
	unittests/enum-flags-selftests.c.
	* btrace.c (ftrace_update_caller, ftrace_fixup_calle): Use
	btrace_function_flags instead of enum btrace_function_flag.
	* compile/compile-c-types.c (convert_qualified): Use
	enum_flags::raw.
	* compile/compile-cplus-symbols.c (convert_one_symbol)
	(convert_symbol_bmsym):
	* compile/compile-cplus-types.c (compile_cplus_convert_method)
	(compile_cplus_convert_struct_or_union_methods)
	(compile_cplus_instance::convert_qualified_base):
	* go-exp.y (parse_string_or_char): Add cast to int.
	* unittests/enum-flags-selftests.c: New file.
	* record-btrace.c (btrace_thread_flag_to_str): Change parameter's
	type to btrace_thread_flags from btrace_thread_flag.
	(record_btrace_cancel_resume, record_btrace_step_thread): Change
	local's type to btrace_thread_flags from btrace_thread_flag.  Add
	cast in DEBUG call.

gdbsupport/ChangeLog:

	* enum-flags.h: Include "traits.h".
	(DEF_ENUM_FLAGS_TYPE): Declare a function instead of defining a
	structure.
	(enum_underlying_type): Update comment.
	(namespace enum_flags_detail): New.  Move struct zero_type here.
	(EnumIsUnsigned, EnumIsSigned): New.
	(class enum_flags): Make most methods constexpr.
	(operator&=, operator|=, operator^=): Take an enum_flags instead
	of an enum_type.  Make rvalue ref versions deleted.
	(operator enum_type()): Delete.
	(operator&, operator|, operator^, operator~): Delete, moved out of
	class.
	(raw()): New method.
	(is_enum_flags_enum_type_t): Declare.
	(ENUM_FLAGS_GEN_BINOP, ENUM_FLAGS_GEN_COMPOUND_ASSIGN)
	(ENUM_FLAGS_GEN_COMP): New.  Use them to reimplement global
	operators.
	(operator~): Now constexpr and reimplemented.
	(operator<<, operator>>): New deleted functions.
	* valid-expr.h (CHECK_VALID_EXPR_5, CHECK_VALID_EXPR_6): New.

1 files changed, 586 insertions, 0 deletions

diff --git a/gdb/unittests/enum-flags-selftests.c b/gdb/unittests/enum-flags-selftests.c
new file mode 100644
index 0000000..af585f0
--- /dev/null
+++ b/gdb/unittests/enum-flags-selftests.c
@@ -0,0 +1,586 @@
+/* Self tests for enum-flags for GDB, the GNU debugger.
+
+   Copyright (C) 2016-2020 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include "defs.h"
+#include "gdbsupport/enum-flags.h"
+#include "gdbsupport/valid-expr.h"
+#include "gdbsupport/selftest.h"
+
+namespace selftests {
+namespace enum_flags_tests {
+
+/* The (real) enum types used in CHECK_VALID.  Their names match the
+   template parameter names of the templates defined by CHECK_VALID to
+   make it simpler to use.  They could be named differently.  */
+
+/* A "real enum".  */
+enum RE
+  {
+    RE_FLAG1 = 1 << 1,
+    RE_FLAG2 = 1 << 2,
+  };
+
+/* Another "real enum".  */
+enum RE2
+  {
+    RE2_FLAG1 = 1 << 1,
+    RE2_FLAG2 = 1 << 2,
+  };
+
+/* An unsigned "real enum".  */
+enum URE : unsigned
+  {
+    URE_FLAG1 = 1 << 1,
+    URE_FLAG2 = 1 << 2,
+    URE_FLAG3 = 0xffffffff,
+  };
+
+/* A non-flags enum.  */
+enum NF
+  {
+    NF_FLAG1 = 1 << 1,
+    NF_FLAG2 = 1 << 2,
+  };
+
+/* The corresponding "enum flags" types.  */
+DEF_ENUM_FLAGS_TYPE (RE, EF);
+DEF_ENUM_FLAGS_TYPE (RE2, EF2);
+DEF_ENUM_FLAGS_TYPE (URE, UEF);
+
+#if HAVE_IS_TRIVIALLY_COPYABLE
+
+/* So that std::vectors of types that have enum_flags fields can
+   reallocate efficiently memcpy.  */
+gdb_static_assert (std::is_trivially_copyable<EF>::value);
+
+#endif
+
+/* A couple globals used as lvalues in the CHECK_VALID expressions
+   below.  Their names (and types) match the uppercase type names
+   exposed by CHECK_VALID just to make the expressions easier to
+   follow.  */
+static RE re ATTRIBUTE_UNUSED;
+static EF ef ATTRIBUTE_UNUSED;
+
+/* First, compile-time tests that:
+
+   - make sure that incorrect operations with mismatching enum types
+     are caught at compile time.
+
+   - make sure that the same operations but involving the right enum
+     types do compile and that they return the correct type.
+*/
+
+#define CHECK_VALID(VALID, EXPR_TYPE, EXPR)		\
+  CHECK_VALID_EXPR_6 (EF, RE, EF2, RE2, UEF, URE, VALID, EXPR_TYPE, EXPR)
+
+typedef std::underlying_type<RE>::type und;
+
+/* Test construction / conversion from/to different types.  */
+
+/* RE/EF -> underlying (explicit) */
+CHECK_VALID (true,  und,  und (RE ()))
+CHECK_VALID (true,  und,  und (EF ()))
+
+/* RE/EF -> int (explicit) */
+CHECK_VALID (true,  int,  int (RE ()))
+CHECK_VALID (true,  int,  int (EF ()))
+
+/* other -> RE */
+
+/* You can construct a raw enum value from an int explicitly to punch
+   a hole in the type system if need to.  */
+CHECK_VALID (true,  RE,   RE (1))
+CHECK_VALID (true,  RE,   RE (RE2 ()))
+CHECK_VALID (false, void, RE (EF2 ()))
+CHECK_VALID (true,  RE,   RE (RE ()))
+CHECK_VALID (false, void, RE (EF ()))
+
+/* other -> EF.  */
+
+/* As expected, enum-flags is a stronger type than the backing raw
+   enum.  Unlike with raw enums, you can't construct an enum flags
+   from an integer nor from an unrelated enum type explicitly.  Add an
+   intermediate conversion via the raw enum if you really need it.  */
+CHECK_VALID (false, void, EF (1))
+CHECK_VALID (false, void, EF (1u))
+CHECK_VALID (false, void, EF (RE2 ()))
+CHECK_VALID (false, void, EF (EF2 ()))
+CHECK_VALID (true,  EF,   EF (RE ()))
+CHECK_VALID (true,  EF,   EF (EF ()))
+
+/* Test operators.  */
+
+/* operator OP (raw_enum, int) */
+
+CHECK_VALID (false, void, RE () | 1)
+CHECK_VALID (false, void, RE () & 1)
+CHECK_VALID (false, void, RE () ^ 1)
+
+/* operator OP (int, raw_enum) */
+
+CHECK_VALID (false, void, 1 | RE ())
+CHECK_VALID (false, void, 1 & RE ())
+CHECK_VALID (false, void, 1 ^ RE ())
+
+/* operator OP (enum_flags, int) */
+
+CHECK_VALID (false, void, EF () | 1)
+CHECK_VALID (false, void, EF () & 1)
+CHECK_VALID (false, void, EF () ^ 1)
+
+/* operator OP (int, enum_flags) */
+
+CHECK_VALID (false, void, 1 | EF ())
+CHECK_VALID (false, void, 1 & EF ())
+CHECK_VALID (false, void, 1 ^ EF ())
+
+/* operator OP (raw_enum, raw_enum) */
+
+CHECK_VALID (false, void, RE () | RE2 ())
+CHECK_VALID (false, void, RE () & RE2 ())
+CHECK_VALID (false, void, RE () ^ RE2 ())
+CHECK_VALID (true,  RE,   RE () | RE ())
+CHECK_VALID (true,  RE,   RE () & RE ())
+CHECK_VALID (true,  RE,   RE () ^ RE ())
+
+/* operator OP (enum_flags, raw_enum) */
+
+CHECK_VALID (false, void, EF () | RE2 ())
+CHECK_VALID (false, void, EF () & RE2 ())
+CHECK_VALID (false, void, EF () ^ RE2 ())
+CHECK_VALID (true,  EF,   EF () | RE ())
+CHECK_VALID (true,  EF,   EF () & RE ())
+CHECK_VALID (true,  EF,   EF () ^ RE ())
+
+/* operator OP= (raw_enum, raw_enum), rvalue ref on the lhs. */
+
+CHECK_VALID (false, void, RE () |= RE2 ())
+CHECK_VALID (false, void, RE () &= RE2 ())
+CHECK_VALID (false, void, RE () ^= RE2 ())
+CHECK_VALID (false, void, RE () |= RE ())
+CHECK_VALID (false, void, RE () &= RE ())
+CHECK_VALID (false, void, RE () ^= RE ())
+
+/* operator OP= (raw_enum, raw_enum), lvalue ref on the lhs. */
+
+CHECK_VALID (false, void, re |= RE2 ())
+CHECK_VALID (false, void, re &= RE2 ())
+CHECK_VALID (false, void, re ^= RE2 ())
+CHECK_VALID (true,  RE&,  re |= RE ())
+CHECK_VALID (true,  RE&,  re &= RE ())
+CHECK_VALID (true,  RE&,  re ^= RE ())
+
+/* operator OP= (enum_flags, raw_enum), rvalue ref on the lhs.  */
+
+CHECK_VALID (false, void, EF () |= RE2 ())
+CHECK_VALID (false, void, EF () &= RE2 ())
+CHECK_VALID (false, void, EF () ^= RE2 ())
+CHECK_VALID (false, void, EF () |= RE ())
+CHECK_VALID (false, void, EF () &= RE ())
+CHECK_VALID (false, void, EF () ^= RE ())
+
+/* operator OP= (enum_flags, raw_enum), lvalue ref on the lhs.  */
+
+CHECK_VALID (false, void, ef |= RE2 ())
+CHECK_VALID (false, void, ef &= RE2 ())
+CHECK_VALID (false, void, ef ^= RE2 ())
+CHECK_VALID (true,  EF&,  ef |= EF ())
+CHECK_VALID (true,  EF&,  ef &= EF ())
+CHECK_VALID (true,  EF&,  ef ^= EF ())
+
+/* operator OP= (enum_flags, enum_flags), rvalue ref on the lhs.  */
+
+CHECK_VALID (false, void, EF () |= EF2 ())
+CHECK_VALID (false, void, EF () &= EF2 ())
+CHECK_VALID (false, void, EF () ^= EF2 ())
+CHECK_VALID (false, void, EF () |= EF ())
+CHECK_VALID (false, void, EF () &= EF ())
+CHECK_VALID (false, void, EF () ^= EF ())
+
+/* operator OP= (enum_flags, enum_flags), lvalue ref on the lhs.  */
+
+CHECK_VALID (false, void, ef |= EF2 ())
+CHECK_VALID (false, void, ef &= EF2 ())
+CHECK_VALID (false, void, ef ^= EF2 ())
+CHECK_VALID (true,  EF&,  ef |= EF ())
+CHECK_VALID (true,  EF&,  ef &= EF ())
+CHECK_VALID (true,  EF&,  ef ^= EF ())
+
+/* operator~ (raw_enum) */
+
+CHECK_VALID (false,  void,   ~RE ())
+CHECK_VALID (true,   URE,    ~URE ())
+
+/* operator~ (enum_flags) */
+
+CHECK_VALID (false,  void,   ~EF ())
+CHECK_VALID (true,   UEF,    ~UEF ())
+
+/* Check ternary operator.  This exercises implicit conversions.  */
+
+CHECK_VALID (true,  EF,   true ? EF () : RE ())
+CHECK_VALID (true,  EF,   true ? RE () : EF ())
+
+/* These are valid, but it's not a big deal since you won't be able to
+   assign the resulting integer to an enum or an enum_flags without a
+   cast.
+
+   The latter two tests are disabled on older GCCs because they
+   incorrectly fail with gcc 4.8 and 4.9 at least.  Running the test
+   outside a SFINAE context shows:
+
+    invalid user-defined conversion from ‘EF’ to ‘RE2’
+
+   They've been confirmed to compile/pass with gcc 5.3, gcc 7.1 and
+   clang 3.7.  */
+
+CHECK_VALID (true,  int,  true ? EF () : EF2 ())
+CHECK_VALID (true,  int,  true ? EF2 () : EF ())
+#if GCC_VERSION >= 5003 || defined __clang__
+CHECK_VALID (true,  int,  true ? EF () : RE2 ())
+CHECK_VALID (true,  int,  true ? RE2 () : EF ())
+#endif
+
+/* Same, but with an unsigned enum.  */
+
+typedef unsigned int uns;
+
+CHECK_VALID (true,  uns,  true ? EF () : UEF ())
+CHECK_VALID (true,  uns,  true ? UEF () : EF ())
+#if GCC_VERSION >= 5003 || defined __clang__
+CHECK_VALID (true,  uns,  true ? EF () : URE ())
+CHECK_VALID (true,  uns,  true ? URE () : EF ())
+#endif
+
+/* Unfortunately this can't work due to the way C++ computes the
+   return type of the ternary conditional operator.  int isn't
+   implicitly convertible to the raw enum type, so the type of the
+   expression is int.  And then int is not implicitly convertible to
+   enum_flags.
+
+   GCC 4.8 fails to compile this test with:
+     error: operands to ?: have different types ‘enum_flags<RE>’ and ‘int’
+   Confirmed to work with gcc 4.9, 5.3 and clang 3.7.
+*/
+#if GCC_VERSION >= 4009 || defined __clang__
+CHECK_VALID (false, void, true ? EF () : 0)
+CHECK_VALID (false, void, true ? 0 : EF ())
+#endif
+
+/* Check that the ++/--/<</>>/<<=/>>= operators are deleted.  */
+
+CHECK_VALID (false, void, RE ()++)
+CHECK_VALID (false, void, ++RE ())
+CHECK_VALID (false, void, --RE ())
+CHECK_VALID (false, void, RE ()--)
+
+CHECK_VALID (false, void, RE () << 1)
+CHECK_VALID (false, void, RE () >> 1)
+CHECK_VALID (false, void, EF () << 1)
+CHECK_VALID (false, void, EF () >> 1)
+
+CHECK_VALID (false, void, RE () <<= 1)
+CHECK_VALID (false, void, RE () >>= 1)
+CHECK_VALID (false, void, EF () <<= 1)
+CHECK_VALID (false, void, EF () >>= 1)
+
+/* Test comparison operators.  */
+
+CHECK_VALID (false, void, EF () == EF2 ())
+CHECK_VALID (false, void, EF () == RE2 ())
+CHECK_VALID (false, void, RE () == EF2 ())
+
+CHECK_VALID (true,  bool, EF (RE (1)) == EF (RE (1)))
+CHECK_VALID (true,  bool, EF (RE (1)) == RE (1))
+CHECK_VALID (true,  bool, RE (1)      == EF (RE (1)))
+
+CHECK_VALID (false, void, EF () != EF2 ())
+CHECK_VALID (false, void, EF () != RE2 ())
+CHECK_VALID (false, void, RE () != EF2 ())
+
+/* On clang, disable -Wenum-compare due to "error: comparison of two
+   values with different enumeration types [-Werror,-Wenum-compare]".
+   clang doesn't suppress -Wenum-compare in SFINAE contexts.  Not a
+   big deal since misuses like these in GDB will be caught by -Werror
+   anyway.  This check is here mainly for completeness.  */
+#if defined __clang__
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wenum-compare"
+#endif
+CHECK_VALID (true,  bool, RE () == RE2 ())
+CHECK_VALID (true,  bool, RE () != RE2 ())
+#if defined __clang__
+# pragma GCC diagnostic pop
+#endif
+
+CHECK_VALID (true,  bool, EF (RE (1)) != EF (RE (2)))
+CHECK_VALID (true,  bool, EF (RE (1)) != RE (2))
+CHECK_VALID (true,  bool, RE (1)      != EF (RE (2)))
+
+CHECK_VALID (true,  bool, EF () == 0)
+
+/* Check we didn't disable/delete comparison between non-flags enums
+   and unrelated types by mistake.  */
+CHECK_VALID (true,  bool, NF (1) == NF (1))
+CHECK_VALID (true,  bool, NF (1) == int (1))
+CHECK_VALID (true,  bool, NF (1) == char (1))
+
+/* -------------------------------------------------------------------- */
+
+/* Follows misc tests that exercise the API.  Some are compile time,
+   when possible, others are run time.  */
+
+enum test_flag
+  {
+    FLAG1 = 1 << 1,
+    FLAG2 = 1 << 2,
+    FLAG3 = 1 << 3,
+  };
+
+enum test_uflag : unsigned
+  {
+    UFLAG1 = 1 << 1,
+    UFLAG2 = 1 << 2,
+    UFLAG3 = 1 << 3,
+  };
+
+DEF_ENUM_FLAGS_TYPE (test_flag, test_flags);
+DEF_ENUM_FLAGS_TYPE (test_uflag, test_uflags);
+
+static void
+self_test ()
+{
+  /* Check that default construction works.  */
+  {
+    constexpr test_flags f;
+
+    gdb_static_assert (f == 0);
+  }
+
+  /* Check that assignment from zero works.  */
+  {
+    test_flags f (FLAG1);
+
+    SELF_CHECK (f == FLAG1);
+
+    f = 0;
+
+    SELF_CHECK (f == 0);
+  }
+
+  /* Check that construction from zero works.  */
+  {
+    constexpr test_flags zero1 = 0;
+    constexpr test_flags zero2 (0);
+    constexpr test_flags zero3 {0};
+    constexpr test_flags zero4 = {0};
+
+    gdb_static_assert (zero1 == 0);
+    gdb_static_assert (zero2 == 0);
+    gdb_static_assert (zero3 == 0);
+    gdb_static_assert (zero4 == 0);
+  }
+
+  /* Check construction from enum value.  */
+  {
+    gdb_static_assert (test_flags (FLAG1) == FLAG1);
+    gdb_static_assert (test_flags (FLAG2) != FLAG1);
+  }
+
+  /* Check copy/assignment.  */
+  {
+    constexpr test_flags src = FLAG1;
+
+    constexpr test_flags f1 = src;
+    constexpr test_flags f2 (src);
+    constexpr test_flags f3 {src};
+    constexpr test_flags f4 = {src};
+
+    gdb_static_assert (f1 == FLAG1);
+    gdb_static_assert (f2 == FLAG1);
+    gdb_static_assert (f3 == FLAG1);
+    gdb_static_assert (f4 == FLAG1);
+  }
+
+  /* Check moving.  */
+  {
+    test_flags src = FLAG1;
+    test_flags dst = 0;
+
+    dst = std::move (src);
+    SELF_CHECK (dst == FLAG1);
+  }
+
+  /* Check construction from an 'or' of multiple bits.  For this to
+     work, operator| must be overridden to return an enum type.  The
+     builtin version would return int instead and then the conversion
+     to test_flags would fail.  */
+  {
+    constexpr test_flags f = FLAG1 | FLAG2;
+    gdb_static_assert (f == (FLAG1 | FLAG2));
+  }
+
+  /* Similarly, check that "FLAG1 | FLAG2" on the rhs of an assignment
+     operator works.  */
+  {
+    test_flags f = 0;
+    f |= FLAG1 | FLAG2;
+    SELF_CHECK (f == (FLAG1 | FLAG2));
+
+    f &= FLAG1 | FLAG2;
+    SELF_CHECK (f == (FLAG1 | FLAG2));
+
+    f ^= FLAG1 | FLAG2;
+    SELF_CHECK (f == 0);
+  }
+
+  /* Check explicit conversion to int works.  */
+  {
+    constexpr int some_bits (FLAG1 | FLAG2);
+
+    /* And comparison with int works too.  */
+    gdb_static_assert (some_bits == (FLAG1 | FLAG2));
+    gdb_static_assert (some_bits == test_flags (FLAG1 | FLAG2));
+  }
+
+  /* Check operator| and operator|=.  Particularly interesting is
+     making sure that putting the enum value on the lhs side of the
+     expression works (FLAG | f).  */
+  {
+    test_flags f = FLAG1;
+    f |= FLAG2;
+    SELF_CHECK (f == (FLAG1 | FLAG2));
+  }
+  {
+    test_flags f = FLAG1;
+    f = f | FLAG2;
+    SELF_CHECK (f == (FLAG1 | FLAG2));
+  }
+  {
+    test_flags f = FLAG1;
+    f = FLAG2 | f;
+    SELF_CHECK (f == (FLAG1 | FLAG2));
+  }
+
+  /* Check the &/&= operators.  */
+  {
+    test_flags f = FLAG1 & FLAG2;
+    SELF_CHECK (f == 0);
+
+    f = FLAG1 | FLAG2;
+    f &= FLAG2;
+    SELF_CHECK (f == FLAG2);
+
+    f = FLAG1 | FLAG2;
+    f = f & FLAG2;
+    SELF_CHECK (f == FLAG2);
+
+    f = FLAG1 | FLAG2;
+    f = FLAG2 & f;
+    SELF_CHECK (f == FLAG2);
+  }
+
+  /* Check the ^/^= operators.  */
+  {
+    constexpr test_flags f = FLAG1 ^ FLAG2;
+    gdb_static_assert (f == (FLAG1 ^ FLAG2));
+  }
+
+  {
+    test_flags f = FLAG1 ^ FLAG2;
+    f ^= FLAG3;
+    SELF_CHECK (f == (FLAG1 | FLAG2 | FLAG3));
+    f = f ^ FLAG3;
+    SELF_CHECK (f == (FLAG1 | FLAG2));
+    f = FLAG3 ^ f;
+    SELF_CHECK (f == (FLAG1 | FLAG2 | FLAG3));
+  }
+
+  /* Check operator~.  Note this only compiles with unsigned
+     flags.  */
+  {
+    constexpr test_uflags f1 = ~UFLAG1;
+    constexpr test_uflags f2 = ~f1;
+    gdb_static_assert (f2 == UFLAG1);
+  }
+
+  /* Check the ternary operator.  */
+
+  {
+    /* raw enum, raw enum */
+    constexpr test_flags f1 = true ? FLAG1 : FLAG2;
+    gdb_static_assert (f1 == FLAG1);
+    constexpr test_flags f2 = false ? FLAG1 : FLAG2;
+    gdb_static_assert (f2 == FLAG2);
+  }
+
+  {
+    /* enum flags, raw enum */
+    constexpr test_flags src = FLAG1;
+    constexpr test_flags f1 = true ? src : FLAG2;
+    gdb_static_assert (f1 == FLAG1);
+    constexpr test_flags f2 = false ? src : FLAG2;
+    gdb_static_assert (f2 == FLAG2);
+  }
+
+  {
+    /* enum flags, enum flags */
+    constexpr test_flags src1 = FLAG1;
+    constexpr test_flags src2 = FLAG2;
+    constexpr test_flags f1 = true ? src1 : src2;
+    gdb_static_assert (f1 == src1);
+    constexpr test_flags f2 = false ? src1 : src2;
+    gdb_static_assert (f2 == src2);
+  }
+
+  /* Check that we can use flags in switch expressions (requires
+     unambiguous conversion to integer).  Also check that we can use
+     operator| in switch cases, where only constants are allowed.
+     This should work because operator| is constexpr.  */
+  {
+    test_flags f = FLAG1 | FLAG2;
+    bool ok = false;
+
+    switch (f)
+      {
+      case FLAG1:
+	break;
+      case FLAG2:
+	break;
+      case FLAG1 | FLAG2:
+	ok = true;
+	break;
+      }
+
+    SELF_CHECK (ok);
+  }
+}
+
+} /* namespace enum_flags_tests */
+} /* namespace selftests */
+
+void _initialize_enum_flags_selftests ();
+
+void
+_initialize_enum_flags_selftests ()
+{
+  selftests::register_test ("enum-flags",
+			    selftests::enum_flags_tests::self_test);
+}