The following patch attempts to implement the C++26 P3378R2 - constexpr
exception types paper.
This is quite complicated, because most of these classes which should
be constexpr-ized use solely or mostly out of line definitions in
libstdc++, both for historical, code size and dual ABI reasons, so that
one can throw these as exceptions between TUs with old vs. new (or vice
versa) ABIs.
For this reason, logic_error/runtime_error and classes derived from it
have the old ABI std::string object inside of them and the exported
APIs from libstdc++.so.6 ensure the right thing.
Now, because new invoked during constant evaluation needs to be deleted
during the same constant evaluation and can't leak into the constant
expressions, I think we don't have to use COW strings under the hood
(which aren't constexpr I guess because of reference counting/COW) and
we can use something else, the patch uses heap allocated std::string
object (where __cow_constexpr_string class has just a pointer to that).
As I think we still want to hide the ugly details if !consteval in the
library, the patch exports 8 __cow_string class symbols (6 existing which
were previously just not exported and 2 new ones) and if !consteval
calls those through extern "C" _Zmangled_name symbols. The functions
are always_inline.
And then logic_error etc. have for C++26 (precisely for
__cpp_lib_constexpr_exceptions >= 202502L) constexpr definitions of
cdtors/methods. This results in slightly larger code (a few insns at most)
at runtime for C++26, e.g. instead of calling say some logic error
cdtor/method with 2 arguments it calls some __cow_string one with 2
arguments but + 8 bytes pointer additions on both.
The patch also removes the __throw_format_error forward declaration
which apparently wasn't needed for anything as all __throw_format_error
users were either in <format> or included <format> before the uses,
reverts the
https://gcc.gnu.org/pipermail/libstdc++/2025-July/062598.html
patch and makes sure __throw_* functions (only those for exception types
which the P3378R2 or P3068R5 papers made constexpr usable and there are
actually constexpr/consteval uses of those) are constexpr for C++26
constexpr exceptions.
The patch does that by splitting the bits/functexcept.h header:
1) bits/functexcept.h stays for the __throw_* functions which are (at
least for now) never constexpr (the <ios>, <system_error>, <future>
and <functional> std::exception derived classes) or are never used
or never used in constexpr/consteval contexts (<exception>, <typeinfo>
std::exception derived classes and std::range_error).
2) bits/new_{throw,except}.h for __throw_bad_alloc/__throw_bad_array_new_length
and std::bad_alloc/std::bad_array_new_length (where <new> includes
<bits/new_except.h> and <bits/new_throw.h> as well for the C++26 constexpr
exceptions case)
3) for the most complicated <stdexcept> stuff, one header
addition to bits/stdexcept.h one header for the __throw_logic_error etc.
forward declarations, one header for the __throw_logic_error etc.
definitions and one header without header guards which will
depending on __glibcxx_exc_in_string include one or the other because
<string> vs. <string_view> vs. <stdexcept> have heavy interdependencies
2025-12-11 Jakub Jelinek <jakub@redhat.com>
PR libstdc++/121114
libstdc++-v3/
* include/bits/version.def: Implement C++26 P3378R2 - constexpr
exception types.
(constexpr_exceptions): Change value from 1 to 202502, remove
no_stdname and TODO comments.
* include/bits/version.h: Regenerate.
* src/c++11/cow-stdexcept.cc (__cow_string(const char*)): New
ctor.
(__cow_string::c_str()): New method.
* config/abi/pre/gnu.ver (GLIBCXX_3.4.35): Export 8 __cow_string
symbols.
* include/bits/new_except.h: New file.
* include/bits/new_throw.h: New file.
* include/bits/stdexcept_throw.h: New file.
* include/bits/stdexcept_throwdef.h: New file.
* include/bits/stdexcept_throwfwd.h: New file.
* include/std/stdexcept: Include bits/stdexcept_except.h and move
everything after <string> include except for std::range_error into
include/bits/stdexcept_except.h.
(std::range_error): If __cpp_lib_constexpr_exceptions >= 202502L
make all cdtors and methods constexpr.
* include/bits/stdexcept_except.h: New file.
* include/std/optional (__glibcxx_want_constexpr_exceptions): Define
before including bits/version.h.
(bad_optional_access::what): Make constexpr for
__cpp_lib_constexpr_exceptions >= 202502L.
(__throw_bad_optional_access): Likewise.
* include/std/expected (__glibcxx_want_constexpr_exceptions): Define
before including bits/version.h.
(bad_expected_access): Make cdtors and all methods constexpr for
__cpp_lib_constexpr_exceptions >= 202502L.
* include/std/format (__glibcxx_want_constexpr_exceptions): Define
before including bits/version.h.
(_GLIBCXX_CONSTEXPR_FORMAT_ERROR): Define and undef later.
(format_error): Use _GLIBCXX_CONSTEXPR_FORMAT_ERROR on ctors.
* include/std/variant (__glibcxx_want_constexpr_exceptions): Define
before including bits/version.h.
(_GLIBCXX_CONSTEXPR_BAD_VARIANT_ACCESS): Define and undef later.
(bad_variant_access): Use it on ctors and what() method.
(__throw_bad_variant_access): Use it here too.
* testsuite/18_support/exception/version.cc: Adjust expected
__cpp_lib_constexpr_exceptions value.
* testsuite/19_diagnostics/runtime_error/constexpr.cc: New test.
* testsuite/19_diagnostics/headers/stdexcept/version.cc: New test.
* testsuite/19_diagnostics/logic_error/constexpr.cc: New test.
* testsuite/20_util/expected/observers.cc (test_value_throw): Change
return type to bool from void, return true at the end, add test
to dereference what() first character. Make it constexpr for
__cpp_lib_constexpr_exceptions >= 202502L and add static_assert.
* testsuite/20_util/expected/version.cc: Add tests for
__cpp_lib_constexpr_exceptions value.
* testsuite/20_util/variant/constexpr.cc: For
__cpp_lib_constexpr_exceptions >= 202502L include <string>.
(test_get): New function if __cpp_lib_constexpr_exceptions >= 202502L,
assert calling it is true.
* testsuite/20_util/variant/version.cc: Add tests for
__cpp_lib_constexpr_exceptions value.
* testsuite/20_util/optional/constexpr/observers/3.cc: Include
testsuite_hooks.h.
(eat, test01): New functions. Assert test01() is true.
* testsuite/20_util/optional/version.cc: Add tests for
__cpp_lib_constexpr_exceptions value.
* include/std/future: Add #include <bits/functexcept.h>.
* include/std/shared_mutex: Include <bits/new_throw.h>.
* include/std/flat_map: Include <bits/stdexcept_throw.h> instead of
<bits/functexcept.h>.
* include/std/syncstream: Remove <bits/functexcept.h> include.
* include/std/flat_set: Likewise.
* include/std/bitset: Include <bits/stdexcept_throw.h> instead of
<bits/functexcept.h>.
* include/std/string_view: Don't include <bits/functexcept.h>, include
<bits/stdexcept_throw.h> early if __glibcxx_exc_in_string is not
defined and include <bits/stdexcept_throw.h> at the end of
the header again if __glibcxx_exc_in_string is 2 and C++26 constexpr
exceptions are enabled.
(__glibcxx_exc_in_string): Define if __glibcxx_exc_in_string wasn't
defined before including <bits/stdexcept_throw.h>.
* include/std/array: Include <bits/stdexcept_throw.h> instead of
<bits/functexcept.h>.
* include/std/inplace_vector: Likewise.
* include/std/string: Include <bits/stdexcept_except.h> and
<bits/stdexcept_throw.h> after bits/basic_string.tcc include if
C++26 constexpr exceptions are enabled and include
<bits/stdexcept_throw.h> instead of <bits/functexcept.h> early.
(__glibcxx_exc_in_string): Define early to 1, undefine at the end.
* include/std/deque: Include <bits/stdexcept_throw.h>.
* include/bits/new_allocator.h: Include <bits/new_throw.h> instead
of <bits/functexcept.h>.
* include/bits/stl_algobase.h: Remove <bits/functexcept.h> include.
* include/bits/stl_vector.h: Include <bits/stdexcept_throw.h> instead
of <bits/functexcept.h>.
* include/bits/memory_resource.h: Include <bits/new_throw.h> instead
of <bits/functexcept.h>.
* include/bits/functexcept.h: Guard everything after includes with
#if _GLIBCXX_HOSTED.
(__throw_bad_alloc, __throw_bad_array_new_length, __throw_logic_error,
__throw_domain_error, __throw_invalid_argument, __throw_length_error,
__throw_out_of_range, __throw_out_of_range_fmt, __throw_runtime_error,
__throw_overflow_error, __throw_underflow_error): Move declarations to
other headers - <bits/new_throw.h> and <bits/stdexcept_throwfwd.h>.
* include/bits/stl_map.h: Include <bits/stdexcept_throw.h> instead
of <bits/functexcept.h>.
* include/bits/hashtable_policy.h: Include <bits/stdexcept_throw.h>
instead of <bits/functexcept.h>.
* include/bits/formatfwd.h (std::__throw_format_error): Remove
declaration.
* include/bits/specfun.h: Include <bits/stdexcept_throw.h> instead of
<bits/functexcept.h>.
* include/bits/basic_ios.h: Include <bits/functexcept.h>.
* include/bits/locale_classes.h: Likewise.
* include/tr1/cmath: Include <bits/stdexcept_throw.h> instead of
<bits/functexcept.h>.
* include/tr1/memory: Remove <bits/functexcept.h> include.
* include/tr1/array: Include <bits/stdexcept_throw.h>.
* include/ext/vstring_util.h: Include <bits/stdexcept_throw.h> instead
of <bits/functexcept.h>.
* include/ext/bitmap_allocator.h: Include <bits/new_throw.h> instead
of <bits/functexcept.h>.
* include/ext/mt_allocator.h: Likewise.
* include/ext/malloc_allocator.h: Likewise.
* include/ext/debug_allocator.h: Include <bits/stdexcept_throw.h>
instead of <bits/functexcept.h>.
* include/ext/concurrence.h: Include <bits/exception_defines.h>
instead of <bits/functexcept.h>.
* include/ext/throw_allocator.h: Include <bits/new_throw.h> and
<bits/stdexcept_throw.h> instead of <bits/functexcept.h>.
* include/ext/string_conversions.h: Include <bits/stdexcept_throw.h>
instead of <bits/functexcept.h>.
* include/ext/pool_allocator.h: Include <bits/new_throw.h> instead
of <bits/functexcept.h>.
* include/ext/ropeimpl.h: Include <bits/stdexcept_throw.h> instead of
<bits/functexcept.h>.
* include/tr2/dynamic_bitset: Likewise.
* include/experimental/optional: Include <bits/exception_defines.h>
instead of <bits/functexcept.h>.
* include/Makefile.am (bits_freestanding): Add
${bits_srcdir}/{new,stdexcept}_{except,throw}.h
and ${bits_srcdir}/stdexcept_throw{fwd,def}.h.
* include/Makefile.in: Regenerate.
* src/c++17/floating_from_chars.cc: Remove <bits/functexcept.h>
include.
* src/c++11/regex.cc: Likewise.
* src/c++11/functexcept.cc: Likewise.
* src/c++11/snprintf_lite.cc: Include <bits/stdexcept_throw.h> instead
of <bits/functexcept.h>.
* src/c++11/thread.cc: Include <bits/functexcept.h>.
* testsuite/util/testsuite_hooks.h: Include <bits/stdexcept_throw.h>
instead of <bits/functexcept.h>.
* testsuite/util/io/verified_cmd_line_input.cc: Include
<bits/exception_defines.h> instead of <bits/functexcept.h>.
* testsuite/20_util/allocator/105975.cc: Expect different diagnostics
for C++26.
* testsuite/23_containers/inplace_vector/access/capacity.cc: Remove
#error, guard if consteval { return; } with
#ifndef __cpp_lib_constexpr_exceptions.
* testsuite/23_containers/inplace_vector/access/elem.cc: Likewise.
* testsuite/23_containers/inplace_vector/cons/1.cc: Likewise.
* testsuite/23_containers/inplace_vector/cons/from_range.cc: Likewise.
* testsuite/23_containers/inplace_vector/modifiers/single_insert.cc:
Likewise.
* testsuite/23_containers/inplace_vector/modifiers/assign.cc:
Likewise.
* testsuite/23_containers/inplace_vector/modifiers/multi_insert.cc:
Likewise.
* libsupc++/new: Include <bits/new_except.h>.
(std::bad_alloc, std::bad_array_new_length): Move defintion to
<bits/new_except.h>.
libgomp/
* omp.h.in: Include <bits/new_throw.h> instead of
<bits/functexcept.h>.
gcc/testsuite/
* g++.dg/tree-ssa/pr110819.C: Guard scan-tree-dump-not delete on
c++23_down and add comment explaining why C++26 fails that.
* g++.dg/tree-ssa/pr96945.C: Likewise.
* g++.dg/tree-ssa/pr109442.C: Likewise.
* g++.dg/tree-ssa/pr116868.C: Likewise.
* g++.dg/tree-ssa/pr58483.C: Likewise.
PR middle-end/109849
* include/bits/c++config (std::__terminate): Mark cold.
* include/bits/functexcept.h: Mark everything as cold.
* libsupc++/exception: Mark terminate and unexpected as cold.
We don't compile src/c++11/functexcept.cc for freestanding, so just
define the functions used by freestanding entities as inline calls to
std::terminate.
libstdc++-v3/ChangeLog:
PR libstdc++/107135
* include/bits/functexcept.h [!_GLIBCXX_HOSTED]
(__throw_invalid_argument, __throw_out_of_range)
(__throw_out_of_range_fmt, __throw_runtime_error)
(__throw_overflow_error): Define inline.
* include/std/bitset (_M_copy_from_ptr) [!_GLIBCXX_HOSTED]:
Replace __builtin_abort with __throw_invalid_argument.
std::allocator and std::pmr::polymorphic_allocator should throw
std::bad_array_new_length from their allocate member functions if the
number of bytes required cannot be represented in std::size_t.
libstdc++-v3/ChangeLog:
* config/abi/pre/gnu.ver: Add new symbol.
* include/bits/functexcept.h (__throw_bad_array_new_length):
Declare new function.
* include/ext/malloc_allocator.h (malloc_allocator::allocate):
Throw bad_array_new_length for impossible sizes (LWG 3190).
* include/ext/new_allocator.h (new_allocator::allocate):
Likewise.
* include/std/memory_resource (polymorphic_allocator::allocate)
(polymorphic_allocator::allocate_object): Use new function,
__throw_bad_array_new_length.
* src/c++11/functexcept.cc (__throw_bad_array_new_length):
Define.
* testsuite/20_util/allocator/lwg3190.cc: New test.
[ios::failure] p2: "When throwing ios_base::failure exceptions,
implementations should provide values of ec that identify the specific
reason for the failure."
This adds a new overload of __throw_ios_failure that can be passed
errno, to store error_code(errno, system_category()) in the exception
object.
PR libstdc++/85343
* acinclude.m4 (libtool_VERSION): Bump version.
* config/abi/pre/gnu.ver (GLIBCXX_3.4.26): Add new symbol version.
Export new symbol.
* configure: Regenerate.
* doc/xml/manual/abi.xml: Document new versions.
* include/bits/fstream.tcc (basic_filebuf<C, T>::underflow)
(basic_filebuf<C, T>::xsgetn): Pass errno to __throw_ios_failure.
* include/bits/functexcept.h (__throw_ios_failure(const char*, int)):
Declare new overload.
* src/c++11/cxx11-ios_failure.cc (__ios_failure): Add new constructor
and static member function.
(__throw_ios_failure(const char*, int)): Define.
* src/c++98/ios_failure.cc [!_GLIBCXX_USE_DUAL_ABI]
(__throw_ios_failure(const char*, int)): Define.
* testsuite/util/testsuite_abi.cc: Update known and latest versions.
From-SVN: r263535
2010-11-18 Benjamin Kosnik <bkoz@redhat.com>
* config/*/*: Use headername alias to associate private includes
to public includes.
* include/*/*: Same.
* scripts/run_doxygen: Update for doxygen 1.7.2.
* doc/doxygen/user.cfg.in: Same.
* doc/doxygen/TODO: Remove.
* testsuite/*/std_c++0x_neg.cc: Adjust line number.
From-SVN: r168046
2005-01-23 Paolo Carlini <pcarlini@suse.de>
Andreas Jaeger <aj@suse.de>
PR libstdc++/19343
* include/bits/functexcept.h: Mark the helpers as 'noreturn'.
Co-Authored-By: Andreas Jaeger <aj@suse.de>
From-SVN: r94106
Jakub Jelinek