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.
When the scope of a qualified name is the current instantiation, and
qualified lookup finds nothing at template definition time, then we
know it'll find nothing at instantiation time (unless the current
instantiation has dependent bases). So such qualified name lookup
failure can be diagnosed ahead of time as per [temp.res.general]/6.
This patch implements that, for qualified names of the form (where
the current instantiation is A<T>):
this->non_existent
a.non_existent
A::non_existent
typename A::non_existent
It turns out we already optimistically attempt qualified lookup of
seemingly every qualified name, even when it's dependently scoped, and
then suppress issuing a lookup failure diagnostic after the fact.
So implementing this is mostly a matter of restricting the diagnostic
suppression to "dependentish" scopes (i.e. dependent scopes or the
current instantiation with dependent bases), rather than suppressing
for any dependently-typed scope as we currently do.
The cp_parser_conversion_function_id change is needed to avoid regressing
lookup/using8.C:
using A<T>::operator typename A<T>::Nested*;
When looking up A<T>::Nested we consider it not dependently scoped since
we entered A<T> from cp_parser_conversion_function_id earlier. But this
A<T> is the implicit instantiation A<T> not the primary template type A<T>,
and so the lookup fails which we now diagnose. This patch works around
this by not entering the template scope of a qualified conversion
function-id in this case, i.e. if we're in an expression vs declaration
context, by seeing if the type already went through finish_template_type
with entering_scope=true.
gcc/cp/ChangeLog:
* decl.cc (make_typename_type): Restrict name lookup failure
punting to dependentish_scope_p instead of dependent_type_p.
* error.cc (qualified_name_lookup_error): Improve diagnostic
when the scope is the current instantiation.
* parser.cc (cp_parser_diagnose_invalid_type_name): Likewise.
(cp_parser_conversion_function_id): Don't call push_scope on
a template scope unless we're in a declaration context.
(cp_parser_lookup_name): Restrict name lookup failure
punting to dependentish_scope_p instead of depedent_type_p.
* semantics.cc (finish_id_expression_1): Likewise.
* typeck.cc (finish_class_member_access_expr): Likewise.
libstdc++-v3/ChangeLog:
* include/experimental/socket
(basic_socket_iostream::basic_socket_iostream): Fix typo.
* include/tr2/dynamic_bitset
(__dynamic_bitset_base::_M_is_proper_subset_of): Likewise.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/alignas18.C: Expect name lookup error for U::X.
* g++.dg/cpp0x/forw_enum13.C: Expect name lookup error for
D3::A and D4<T>::A.
* g++.dg/parse/access13.C: Declare A::E::V to avoid name lookup
failure and preserve intent of the test.
* g++.dg/parse/enum11.C: Expect extra errors, matching the
non-template case.
* g++.dg/template/crash123.C: Avoid name lookup failure to
preserve intent of the test.
* g++.dg/template/crash124.C: Likewise.
* g++.dg/template/crash7.C: Adjust expected diagnostics.
* g++.dg/template/dtor6.C: Declare A::~A() to avoid name lookup
failure and preserve intent of the test.
* g++.dg/template/error22.C: Adjust expected diagnostics.
* g++.dg/template/static30.C: Avoid name lookup failure to
preserve intent of the test.
* g++.old-deja/g++.other/decl5.C: Adjust expected diagnostics.
* g++.dg/template/non-dependent34.C: New test.
Reviewed-by: Jason Merrill <jason@redhat.com>
The shift operations for dynamic_bitset fail to zero out words where the
non-zero bits were shifted to a completely different word.
For a right shift we don't need to sanitize the unused bits in the high
word, because we know they were already clear and a right shift doesn't
change that.
libstdc++-v3/ChangeLog:
PR libstdc++/115399
* include/tr2/dynamic_bitset (operator>>=): Remove redundant
call to _M_do_sanitize.
* include/tr2/dynamic_bitset.tcc (_M_do_left_shift): Zero out
low bits in words that should no longer be populated.
(_M_do_right_shift): Likewise for high bits.
* testsuite/tr2/dynamic_bitset/pr115399.cc: New test.
These non-standard extensions use GCC-specific built-ins. Use
__has_builtin to avoid errors when Clang compiles this header.
See https://github.com/llvm/llvm-project/issues/24289
libstdc++-v3/ChangeLog:
* include/tr2/type_traits (bases, direct_bases): Use
__has_builtin to check if required built-ins are supported.
libstdc++-v3/ChangeLog:
* include/tr2/dynamic_bitset (dynamic_bitset): Pass zero and one
characters to _M_copy_from_string.
* testsuite/tr2/dynamic_bitset/string.cc: New test.
PR libstdc++/92059
* include/tr2/dynamic_bitset (__dynamic_bitset_base): Define all
special member functions as defaulted. Add noexcept to most members.
(__dynamic_bitset_base(size_t, unsigned long long, const _Alloc&)):
Mask off unwanted bits in the __val parameter. Avoid undefined left
shifts.
(__dynamic_bitset_base::_M_assign): Remove.
(__dynamic_bitset_base::_M_do_reset): Use std::fill.
(__dynamic_bitset_base::_M_are_all_aux): Avoid integer promotion when
block_type has lower rank than int.
(dynamic_bitset): Add noexcept to most members. Use injected-class-name
in return types and parameter types.
(dynamic_bitset::_M_Nb): Add default member initializer.
(dynamic_bitset(), dynamic_bitset(const dynamic_bitset&)): Define as
defaulted.
(dynamic_bitset(dynamic_bitset&&)): Clear source object after move.
(dynamic_bitset::operator=(const dynamic_bitset&)): Define as
defaulted.
(dynamic_bitset::operator=(dynamic_bitset&&)): Add noexcept-specifier.
Define without using swap, to propagate allocator correctly.
(dynamic_bitset(const char*, const _Alloc&)): Use strlen.
(dynamic_bitset::_M_do_sanitize, dynamic_bitset::_M_do_fill): Use
casts to avoid unwanted integer promotions.
(dynamic_bitset::_M_copy_from_ptr): Rearrange template parameters and
add default template arguments and default argument to simplify usage.
(dynamic_bitset::_M_copy_from_string): Adjust call to _M_copy_from_ptr.
(operator==(const dynamic_bitset&, const dynamic_bitset&))
(operator<(const dynamic_bitset&, const dynamic_bitset&)): Use _M_Nb.
* include/tr2/dynamic_bitset.tcc (dynamic_bitset::_M_copy_from_ptr):
Adjust template parameters to match declaration.
* testsuite/tr2/dynamic_bitset/cmp.cc: New test.
* testsuite/tr2/dynamic_bitset/cons.cc: New test.
* testsuite/tr2/dynamic_bitset/copy.cc: New test.
* testsuite/tr2/dynamic_bitset/move.cc: New test.
* testsuite/tr2/dynamic_bitset/pr92059.cc: New test.
From-SVN: r276890
Previously the _M_Nb member was incremented before calling
_M_unchecked_set which meant that the bit being set was out of bounds.
It either set the wrong bit in an allocated word, or accessed beyond the
end of the allocated memory in the _M_w vector. The fix for the bug is
to update the _M_Nb member after using it as an index.
As an optimisation, when a new block needs to be appended the call to
_M_unchecked_set can be avoided by appending a block with the least
significant bit already set to the desired value.
PR libstdc++/87784
* include/tr2/dynamic_bitset (dynamic_bitset::push_back): When there
are no unused bits in the last block, append a new block with the
right value so the bit doesn't need to be set. Only increment size
after setting the new bit, not before.
* testsuite/tr2/dynamic_bitset/pr87784.cc: New test.
From-SVN: r265625
