Backport gdb patch to fix integer value -1 outside valid range error in clang 16+

[yanyir]

When building crash with clang 17, I encountered numerous error: integer value -1 is outside the valid range of values errors, such as:

./../gdbsupport/enum-flags.h:85:52: error: integer value -1 is outside the valid range of values [0, 15] for the enumeration type 'ui_out_flag' [-Wenum-constexpr-conversion]
   85 |     integer_for_size<sizeof (T), static_cast<bool>(T (-1) < T (0))>::type
      |                                                    ^
In file included from cp-valprint.c:20:
In file included from ./defs.h:65:
./../gdbsupport/enum-flags.h:85:52: error: integer value -1 is outside the valid range of values [0, 15] for the enumeration type 'ui_out_flag' [-Wenum-constexpr-conversion]
   85 |     integer_for_size<sizeof (T), static_cast<bool>(T (-1) < T (0))>::type
      |                                                    ^
In file included from d-lang.c:20:
In file included from ./defs.h:65:
./../gdbsupport/enum-flags.h:85:52: error: integer value -1 is outside the valid range of values [0, 15] for the enumeration type 'ui_out_flag' [-Wenum-constexpr-conversion]
   85 |     integer_for_size<sizeof (T), static_cast<bool>(T (-1) < T (0))>::type
      |                                                    ^
In file included from cp-namespace.c:21:
In file included from ./defs.h:65:
./../gdbsupport/enum-flags.h:85:52: error: integer value -1 is outside the valid range of values [0, 15] for the enumeration type 'ui_out_flag' [-Wenum-constexpr-conversion]
   85 |     integer_for_size<sizeof (T), static_cast<bool>(T (-1) < T (0))>::type
      |                                                    ^
In file included from d-namespace.c:20:
In file included from ./defs.h:65:
./../gdbsupport/enum-flags.h:85:52: error: integer value -1 is outside the valid range of values [0, 15] for the enumeration type 'ui_out_flag' [-Wenum-constexpr-conversion]
   85 |     integer_for_size<sizeof (T), static_cast<bool>(T (-1) < T (0))>::type
      |                                                    ^
In file included from ctfread.c:78:
In file included from ./defs.h:65:
./../gdbsupport/enum-flags.h:85:52: error: integer value -1 is outside the valid range of values [0, 15] for the enumeration type 'ui_out_flag' [-Wenum-constexpr-conversion]
   85 |     integer_for_size<sizeof (T), static_cast<bool>(T (-1) < T (0))>::type
      |                                                    ^
In file included from d-valprint.c:20:
In file included from ./defs.h:65:
./../gdbsupport/enum-flags.h:85:52: error: integer value -1 is outside the valid range of values [0, 15] for the enumeration type 'ui_out_flag' [-Wenum-constexpr-conversion]
   85 |     integer_for_size<sizeof (T), static_cast<bool>(T (-1) < T (0))>::type
      |                                                    ^
./../gdbsupport/enum-flags.h:85:52: error: integer value -1 is outside the valid range of values [0, 3] for the enumeration type 'innermost_block_tracker_type' [-Wenum-constexpr-conversion]
./../gdbsupport/enum-flags.h:85:52: error: integer value -1 is outside the valid range of values [0, 3] for the enumeration type 'innermost_block_tracker_type' [-Wenum-constexpr-conversion]
./../gdbsupport/enum-flags.h:85:52: error: integer value -1 is outside the valid range of values [0, 1] for the enumeration type 'btrace_insn_flag' [-Wenum-constexpr-conversion]
./../gdbsupport/enum-flags.h:85:52: error: integer value -1 is outside the valid range of values [0, 3] for the enumeration type 'btrace_function_flag' [-Wenum-constexpr-conversion]
./../gdbsupport/enum-flags.h:85:52: error: integer value -1 is outside the valid range of values [0, 1] for the enumeration type 'btrace_insn_flag' [-Wenum-constexpr-conversion]
./../gdbsupport/enum-flags.h:85:52: error: integer value -1 is outside the valid range of values [0, 3] for the enumeration type 'btrace_function_flag' [-Wenum-constexpr-conversion]
In file included from dbxread.c:33:
In file included from ./defs.h:65:
./../gdbsupport/enum-flags.h:85:52: error: integer value -1 is outside the valid range of values [0, 15] for the enumeration type 'ui_out_flag' [-Wenum-constexpr-conversion]
   85 |     integer_for_size<sizeof (T), static_cast<bool>(T (-1) < T (0))>::type
      |                                                    ^
...

GDB ignore -Wenum-constexpr-conversion around enum-flags.h to solve the problem.

After applying this patch form GDB, my build succeeded.

Related GDB commit：
8cbde735e40551a694d4ee5cfd4d525d3d77ff7e ("gdbsupport: ignore -Wenum-constexpr-conversion in enum-flags.h")

gdbsupport: ignore -Wenum-constexpr-conversion in enum-flags.h

When building with clang 16, we get:

CXX gdb.o
In file included from /home/smarchi/src/binutils-gdb/gdb/gdb.c:19:
In file included from /home/smarchi/src/binutils-gdb/gdb/defs.h:65:
/home/smarchi/src/binutils-gdb/gdb/../gdbsupport/enum-flags.h:95:52: error: integer value -1 is outside the valid range of values [0, 15] for this enumeration type [-Wenum-constexpr-conversion]
integer_for_size<sizeof (T), static_cast(T (-1) < T (0))>::type
^

The error message does not make it clear in the context of which enum
flag this fails (i.e. what is T in this context), but it doesn't really
matter, we have similar warning/errors for many of them, if we let the
build go through.

clang is right that the value -1 is invalid for the enum type we cast -1
to. However, we do need this expression in order to select an integer
type with the appropriate signedness. That is, with the same signedness
as the underlying type of the enum.

I first wondered if that was really needed, if we couldn't use
std::underlying_type for that. It turns out that the comment just above
says:

/* Note that std::underlying_type<enum_type> is not what we want here,
since that returns unsigned int even when the enum decays to signed
int. */

I was surprised, because std::is_signed<std::underlying_type<enum_type>>
returns the right thing. So I tried replacing all this with
std::underlying_type, see if that would work. Doing so causes some
build failures in unittests/enum-flags-selftests.c:

CXX unittests/enum-flags-selftests.o
/home/smarchi/src/binutils-gdb/gdb/unittests/enum-flags-selftests.c:254:1: error: static assertion failed due to requirement 'gdb::is_same<selftests::enum_flags_tests::check_valid_expr254::archetype<enum_flagsselftests::enum_flags_tests::RE, selftests::enum_flags_tests::RE, enum_flagsselftests::enum_flags_tests::RE2, selftests::enum_flags_tests::RE2, enum_flagsselftests::enum_flags_tests::URE, selftests::enum_fla
gs_tests::URE, int>, selftests::enum_flags_tests::check_valid_expr254::archetype<[enum_flagsselftests::enum_flags_tests::RE](https://github.com/crash-utility/crash/compare/enum_flags%3Cselftests::enum_flags_tests::RE), selftests::enum_flags_tests::RE, enum_flagsselftests::enum_flags_tests::RE2, selfte
sts::enum_flags_tests::RE2, enum_flagsselftests::enum_flags_tests::URE, selftests::enum_flags_tests::URE, unsigned int>>::value == true':
CHECK_VALID (true, int, true ? EF () : EF2 ())
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/smarchi/src/binutils-gdb/gdb/unittests/enum-flags-selftests.c:91:3: note: expanded from macro 'CHECK_VALID'
CHECK_VALID_EXPR_6 (EF, RE, EF2, RE2, UEF, URE, VALID, EXPR_TYPE, EXPR)
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/smarchi/src/binutils-gdb/gdb/../gdbsupport/valid-expr.h:105:3: note: expanded from macro 'CHECK_VALID_EXPR_6'
CHECK_VALID_EXPR_INT (ESC_PARENS (typename T1, typename T2,
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/smarchi/src/binutils-gdb/gdb/../gdbsupport/valid-expr.h:66:3: note: expanded from macro 'CHECK_VALID_EXPR_INT'
static_assert (gdb::is_detected_exact<archetype<TYPES, EXPR_TYPE>,
^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This is a bit hard to decode, but basically enumerations have the
following funny property that they decay into a signed int, even if
their implicit underlying type is unsigned. This code:

enum A {};
enum B {};

int main() {
std::cout << std::is_signed<std::underlying_type<A>::type>::value
<< std::endl;
std::cout << std::is_signed<std::underlying_type<B>::type>::value
<< std::endl;
auto result = true ? A() : B();
std::cout << std::is_signed<decltype(result)>::value << std::endl;
}

produces:

0
0
1

So, the "CHECK_VALID" above checks that this property works for enum flags the
same way as it would if you were using their underlying enum types. And
somehow, changing integer_for_size to use std::underlying_type breaks that.

Since the current code does what we want, and I don't see any way of doing it
differently, ignore -Wenum-constexpr-conversion around it.

Change-Id: Ibc82ae7bbdb812102ae3f1dd099fc859dc6f3cc2

[yanyir]

Sorry, I happened to not backport the full patch of commit before. Now it should be complete.