On Sat, 03 Jan 2026 at 02:06 +0100, Jakub Jelinek wrote:
Hi!
As mentioned in
https://gcc.gnu.org/pipermail/gcc-patches/2026-January/704712.html
in the gnu::constexpr_only thread, gnu::gnu_inline attribute actually
seems to work for most of what we need for C++26 constexpr exceptions
(i.e. when we want out of line bodies for C++ < 26 and need to use
constexpr for C++26, yet don't want for reasons mentioned in those
two PRs the bodies of those constexpr methods to be emitted inline).
Unfortunately clang++ doesn't handle it 100% properly and requires
the redundant inline keyword to make it work (even when the methods
are constexpr and thus implicilty inline), g++ doesn't require that,
so the patch adds also the redundant inline keywords and not just
the [[__gnu__::__gnu_inline__]] attribute.
This way if something wants to inline those functions it can, but
if their address is taken, we just rely on libstdc++.{so,a} to provide
those (which it does as before because those TUs are compiled with
older -std= modes).
The only thing that doesn't work best is that the gnu::gnu_inline
constexpr virtual methods aren't key methods, so vtables and rtti
can still be emitted in each TU using those. Will post an incremental
patch for that.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK
2026-01-03 Jakub Jelinek <[email protected]>
PR libstdc++/123183
PR libstdc++/123326
* libsupc++/exception (std::bad_exception::~bad_exception(),
std::bad_exception::what()): Add inline keyword and
[[__gnu__::__gnu_inline__]] attribute to the C++26 constexpr
exceptions definitions.
* libsupc++/exception.h (std::exception::~exception(),
std::exception::what()): Likewise.
* libsupc++/exception_ptr.h (std::exception_ptr::exception_ptr(void*)):
Likewise.
* libsupc++/nested_exception.h
(std::nested_exception::~nested_exception()): Likewise.
* libsupc++/typeinfo (std::bad_cast::~bad_cast(),
std::bad_cast::what(), std::bad_typeid::~bad_typeid(),
std::bad_typeid::what()): Likewise.
* include/bits/new_except.h (std::bad_alloc::~bad_alloc(),
std::bad_alloc::what(),
std::bad_array_new_length::~bad_array_new_length(),
std::bad_array_new_length::what()): Likewise.
* include/bits/stdexcept_except.h
(std::logic_error::logic_error(const string&),
std::logic_error::logic_error(const char*),
std::logic_error::~logic_error(), std::logic_error::what(),
std::domain_error::domain_error(const string&),
std::domain_error::domain_error(const char*),
std::invalid_argument::invalid_argument(const string&),
std::invalid_argument::invalid_argument(const char*),
std::length_error::length_error(const string&),
std::length_error::length_error(const char*),
std::out_of_range::out_of_range(const string&),
std::out_of_range::out_of_range(const char*),
std::runtime_error::runtime_error(const string&),
std::runtime_error::runtime_error(const char*),
std::runtime_error::~runtime_error(), std::runtime_error::what(),
std::overflow_error::overflow_error(const string&),
std::overflow_error::overflow_error(const char*),
std::overflow_error::~overflow_error(),
std::underflow_error::underflow_error(const string&),
std::underflow_error::underflow_error(const char*),
std::underflow_error::~underflow_error()): Likewise.
(std::domain_error::~domain_error(),
std::invalid_argument::~invalid_argument(),
std::length_error::~length_error(),
std::out_of_range::~out_of_range()): Likewise. Also change
_GLIBCXX_NOTHROW to noexcept on those definitions.
--- libstdc++-v3/libsupc++/exception.jj 2026-01-02 09:56:10.650328356 +0100
+++ libstdc++-v3/libsupc++/exception 2026-01-02 15:59:51.015098351 +0100
@@ -61,9 +61,12 @@ namespace std _GLIBCXX_VISIBILITY(defaul
_GLIBCXX26_CONSTEXPR bad_exception() _GLIBCXX_USE_NOEXCEPT { }
#if __cplusplus >= 202400L
- constexpr virtual ~bad_exception() _GLIBCXX_TXN_SAFE_DYN noexcept {}
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline virtual ~bad_exception() _GLIBCXX_TXN_SAFE_DYN noexcept {}
- constexpr virtual const char* what() const _GLIBCXX_TXN_SAFE_DYN noexcept
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline virtual const char* what() const _GLIBCXX_TXN_SAFE_DYN
+ noexcept
{
return "std::bad_exception";
}
--- libstdc++-v3/libsupc++/exception.h.jj 2026-01-02 09:56:10.650328356
+0100
+++ libstdc++-v3/libsupc++/exception.h 2026-01-02 16:00:01.849911625 +0100
@@ -63,7 +63,8 @@ namespace std _GLIBCXX_VISIBILITY(defaul
public:
_GLIBCXX26_CONSTEXPR exception() _GLIBCXX_NOTHROW { }
#if __cplusplus >= 202400L
- constexpr virtual ~exception() _GLIBCXX_TXN_SAFE_DYN noexcept {}
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline virtual ~exception() _GLIBCXX_TXN_SAFE_DYN noexcept {}
#else
virtual ~exception() _GLIBCXX_TXN_SAFE_DYN _GLIBCXX_NOTHROW;
#endif
@@ -77,7 +78,8 @@ namespace std _GLIBCXX_VISIBILITY(defaul
/** Returns a C-style character string describing the general cause
* of the current error. */
#if __cplusplus >= 202400L
- constexpr virtual const char*
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline virtual const char*
what() const _GLIBCXX_TXN_SAFE_DYN noexcept { return "std::exception"; }
#else
virtual const char*
--- libstdc++-v3/libsupc++/exception_ptr.h.jj 2026-01-02 09:56:10.650328356
+0100
+++ libstdc++-v3/libsupc++/exception_ptr.h 2026-01-02 16:00:13.950703080
+0100
@@ -107,7 +107,8 @@ namespace std _GLIBCXX_VISIBILITY(defaul
void* _M_exception_object;
#if __cplusplus >= 202400L
- constexpr explicit exception_ptr(void* __e) noexcept
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline explicit exception_ptr(void* __e) noexcept
: _M_exception_object(__e)
{
if (_M_exception_object)
--- libstdc++-v3/libsupc++/nested_exception.h.jj 2026-01-02
09:56:10.651328339 +0100
+++ libstdc++-v3/libsupc++/nested_exception.h 2026-01-02 16:00:20.339592975
+0100
@@ -72,7 +72,8 @@ namespace std _GLIBCXX_VISIBILITY(defaul
nested_exception& operator=(const nested_exception&) noexcept = default;
#if __cplusplus >= 202400L
- constexpr virtual ~nested_exception() noexcept {}
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline virtual ~nested_exception() noexcept {}
#else
virtual ~nested_exception() noexcept;
#endif
--- libstdc++-v3/libsupc++/typeinfo.jj 2026-01-02 09:56:10.652328322 +0100
+++ libstdc++-v3/libsupc++/typeinfo 2026-01-02 16:00:39.660260006 +0100
@@ -227,9 +227,11 @@ namespace std
_GLIBCXX26_CONSTEXPR bad_cast() _GLIBCXX_USE_NOEXCEPT { }
#if __cplusplus >= 202400L
- constexpr virtual ~bad_cast() noexcept {}
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline virtual ~bad_cast() noexcept {}
- constexpr virtual const char* what() const noexcept
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline virtual const char* what() const noexcept
{
return "std::bad_cast";
}
@@ -253,9 +255,11 @@ namespace std
_GLIBCXX26_CONSTEXPR bad_typeid () _GLIBCXX_USE_NOEXCEPT { }
#if __cplusplus >= 202400L
- constexpr virtual ~bad_typeid() noexcept {}
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline virtual ~bad_typeid() noexcept {}
- constexpr virtual const char* what() const noexcept
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline virtual const char* what() const noexcept
{
return "std::bad_typeid";
}
--- libstdc++-v3/include/bits/new_except.h.jj 2026-01-02 09:56:10.597329251
+0100
+++ libstdc++-v3/include/bits/new_except.h 2026-01-02 15:56:27.258609869
+0100
@@ -62,9 +62,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
#endif
#if __cplusplus >= 202400L
- constexpr virtual ~bad_alloc() noexcept {}
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline virtual ~bad_alloc() noexcept {}
- constexpr virtual const char* what() const noexcept
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline virtual const char* what() const noexcept
{
return "std::bad_alloc";
}
@@ -85,9 +87,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
_GLIBCXX26_CONSTEXPR bad_array_new_length() throw() { }
#if __cplusplus >= 202400L
- constexpr virtual ~bad_array_new_length() noexcept {}
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline virtual ~bad_array_new_length() noexcept {}
- constexpr virtual const char* what() const noexcept
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline virtual const char* what() const noexcept
{
return "std::bad_array_new_length";
}
--- libstdc++-v3/include/bits/stdexcept_except.h.jj 2026-01-02
09:56:10.601329183 +0100
+++ libstdc++-v3/include/bits/stdexcept_except.h 2026-01-02
16:01:33.247336495 +0100
@@ -258,11 +258,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
public:
#if __cpp_lib_constexpr_exceptions >= 202502L
- constexpr explicit
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline explicit
logic_error(const string& __arg) _GLIBCXX_TXN_SAFE
: _M_msg(__arg) {}
- constexpr explicit
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline explicit
logic_error(const char* __arg) _GLIBCXX_TXN_SAFE
: _M_msg(__arg) {}
@@ -271,9 +273,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
constexpr logic_error(const logic_error&) noexcept = default;
constexpr logic_error& operator=(const logic_error&) noexcept = default;
- constexpr virtual ~logic_error() _GLIBCXX_TXN_SAFE_DYN noexcept { }
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline virtual ~logic_error() _GLIBCXX_TXN_SAFE_DYN noexcept { }
- constexpr virtual const char*
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline virtual const char*
what() const _GLIBCXX_TXN_SAFE_DYN noexcept
{
return _M_msg.c_str();
@@ -319,15 +323,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
public:
#if __cpp_lib_constexpr_exceptions >= 202502L
- constexpr explicit domain_error(const string& __arg) _GLIBCXX_TXN_SAFE
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline explicit domain_error(const string& __arg)
+ _GLIBCXX_TXN_SAFE
: logic_error(__arg) { }
- constexpr explicit domain_error(const char* __arg) _GLIBCXX_TXN_SAFE
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline explicit domain_error(const char* __arg) _GLIBCXX_TXN_SAFE
: logic_error(__arg) { }
constexpr domain_error(const domain_error&) = default;
constexpr domain_error& operator=(const domain_error&) = default;
constexpr domain_error(domain_error&&) = default;
constexpr domain_error& operator=(domain_error&&) = default;
- constexpr virtual ~domain_error() _GLIBCXX_NOTHROW { }
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline virtual ~domain_error() noexcept { }
#else
explicit domain_error(const string& __arg) _GLIBCXX_TXN_SAFE;
#if __cplusplus >= 201103L
@@ -346,15 +354,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
public:
#if __cpp_lib_constexpr_exceptions >= 202502L
- constexpr explicit invalid_argument(const string& __arg) _GLIBCXX_TXN_SAFE
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline explicit invalid_argument(const string& __arg)
+ _GLIBCXX_TXN_SAFE
: logic_error(__arg) { }
- constexpr explicit invalid_argument(const char* __arg) _GLIBCXX_TXN_SAFE
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline explicit invalid_argument(const char* __arg)
+ _GLIBCXX_TXN_SAFE
: logic_error(__arg) { }
constexpr invalid_argument(const invalid_argument&) = default;
constexpr invalid_argument& operator=(const invalid_argument&) = default;
constexpr invalid_argument(invalid_argument&&) = default;
constexpr invalid_argument& operator=(invalid_argument&&) = default;
- constexpr virtual ~invalid_argument() _GLIBCXX_NOTHROW { }
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline virtual ~invalid_argument() noexcept { }
#else
explicit invalid_argument(const string& __arg) _GLIBCXX_TXN_SAFE;
#if __cplusplus >= 201103L
@@ -374,15 +387,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
public:
#if __cpp_lib_constexpr_exceptions >= 202502L
- constexpr explicit length_error(const string& __arg) _GLIBCXX_TXN_SAFE
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline explicit length_error(const string& __arg)
+ _GLIBCXX_TXN_SAFE
: logic_error(__arg) { }
- constexpr explicit length_error(const char* __arg) _GLIBCXX_TXN_SAFE
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline explicit length_error(const char* __arg) _GLIBCXX_TXN_SAFE
: logic_error(__arg) { }
constexpr length_error(const length_error&) = default;
constexpr length_error& operator=(const length_error&) = default;
constexpr length_error(length_error&&) = default;
constexpr length_error& operator=(length_error&&) = default;
- constexpr virtual ~length_error() _GLIBCXX_NOTHROW { }
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline virtual ~length_error() noexcept { }
#else
explicit length_error(const string& __arg) _GLIBCXX_TXN_SAFE;
#if __cplusplus >= 201103L
@@ -402,15 +419,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
public:
#if __cpp_lib_constexpr_exceptions >= 202502L
- constexpr explicit out_of_range(const string& __arg) _GLIBCXX_TXN_SAFE
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline explicit out_of_range(const string& __arg)
+ _GLIBCXX_TXN_SAFE
: logic_error(__arg) { }
- constexpr explicit out_of_range(const char* __arg) _GLIBCXX_TXN_SAFE
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline explicit out_of_range(const char* __arg) _GLIBCXX_TXN_SAFE
: logic_error(__arg) { }
constexpr out_of_range(const out_of_range&) = default;
constexpr out_of_range& operator=(const out_of_range&) = default;
constexpr out_of_range(out_of_range&&) = default;
constexpr out_of_range& operator=(out_of_range&&) = default;
- constexpr virtual ~out_of_range() _GLIBCXX_NOTHROW { }
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline virtual ~out_of_range() noexcept { }
#else
explicit out_of_range(const string& __arg) _GLIBCXX_TXN_SAFE;
#if __cplusplus >= 201103L
@@ -435,11 +456,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
public:
#if __cpp_lib_constexpr_exceptions >= 202502L
- constexpr explicit
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline explicit
runtime_error(const string& __arg) _GLIBCXX_TXN_SAFE
: _M_msg(__arg) {}
- constexpr explicit
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline explicit
runtime_error(const char* __arg) _GLIBCXX_TXN_SAFE
: _M_msg(__arg) {}
@@ -448,9 +471,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
constexpr runtime_error(const runtime_error&) noexcept = default;
runtime_error& operator=(const runtime_error&) noexcept = default;
- constexpr virtual ~runtime_error() _GLIBCXX_TXN_SAFE_DYN noexcept { }
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline virtual ~runtime_error() _GLIBCXX_TXN_SAFE_DYN noexcept
+ {}
- constexpr virtual const char*
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline virtual const char*
what() const _GLIBCXX_TXN_SAFE_DYN noexcept
{
return _M_msg.c_str();
@@ -495,15 +521,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
public:
#if __cpp_lib_constexpr_exceptions >= 202502L
- constexpr explicit overflow_error(const string& __arg) _GLIBCXX_TXN_SAFE
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline explicit overflow_error(const string& __arg)
+ _GLIBCXX_TXN_SAFE
: runtime_error(__arg) { }
- constexpr explicit overflow_error(const char* __arg) _GLIBCXX_TXN_SAFE
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline explicit overflow_error(const char* __arg)
+ _GLIBCXX_TXN_SAFE
: runtime_error(__arg) { }
constexpr overflow_error(const overflow_error&) = default;
constexpr overflow_error& operator=(const overflow_error&) = default;
constexpr overflow_error(overflow_error&&) = default;
constexpr overflow_error& operator=(overflow_error&&) = default;
- constexpr virtual ~overflow_error() noexcept { }
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline virtual ~overflow_error() noexcept { }
#else
explicit overflow_error(const string& __arg) _GLIBCXX_TXN_SAFE;
#if __cplusplus >= 201103L
@@ -522,15 +553,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
public:
#if __cpp_lib_constexpr_exceptions >= 202502L
- constexpr explicit underflow_error(const string& __arg) _GLIBCXX_TXN_SAFE
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline explicit underflow_error(const string& __arg)
+ _GLIBCXX_TXN_SAFE
: runtime_error(__arg) { }
- constexpr explicit underflow_error(const char* __arg) _GLIBCXX_TXN_SAFE
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline explicit underflow_error(const char* __arg)
+ _GLIBCXX_TXN_SAFE
: runtime_error(__arg) { }
constexpr underflow_error(const underflow_error&) = default;
constexpr underflow_error& operator=(const underflow_error&) = default;
constexpr underflow_error(underflow_error&&) = default;
constexpr underflow_error& operator=(underflow_error&&) = default;
- constexpr virtual ~underflow_error() noexcept { }
+ [[__gnu__::__gnu_inline__]]
+ constexpr inline virtual ~underflow_error() noexcept { }
#else
explicit underflow_error(const string& __arg) _GLIBCXX_TXN_SAFE;
#if __cplusplus >= 201103L
Jakub
