C++11 forbids a compound statement, as seen in the definition
of __glibcxx_assert(), in a constexpr function. This patch
open-codes the assertion in `bitset<>::operator[] const` for
C++11 to fix a failure in `g++.old-deja/g++.martin/bitset1.C`.
Also, it adds `{ dg-do compile }` in another test to suppress
a spurious UNRESOLVED complaint.
libstdc++-v3/ChangeLog:
* include/std/bitset (operator[]() const): Customize bounds
check for C++11 case.
* testsuite/20_util/bitset/access/subscript_const_neg.cc:
Suppress UNRESOLVED complaint.
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.
According to the standard the first n characters of a bitset constructor
string need to be checked instead of only N.
libstdc++-v3/ChangeLog:
PR libstdc++/121054
* include/std/bitset: Add string check to constructor.
* testsuite/20_util/bitset/121054.cc: New test.
* testsuite/20_util/bitset/cons/constexpr_c++23.cc: Fix.
Co-authored-by: Jonathan Wakely <jwakely@redhat.com>
Asking std::is_constructible_v<std::bitset<1>, NonTrivial*> gives an
error, rather than answering the query. The problem is that the
constructor for std::bitset("010101") is not constrained to only accept
pointers to char-like types, and for the second parameter (which has a
default argument) std::basic_string_view<CharT> gets instantiated. If
the type is not char-like then that has undefined behaviour, and might
trigger a static_assert to fail in the body of std::basic_string_view.
We can fix it by constraining that constructor using the requirements
for char-like types from [strings.general] p1. I've submitted LWG 4294
and proposed making this change in the standard.
libstdc++-v3/ChangeLog:
PR libstdc++/121046
* include/std/bitset (bitset(const CharT*, ...)): Add
constraints on CharT type.
* testsuite/23_containers/bitset/lwg4294.cc: New test.
This change was part of by P2697R1 (Interfacing bitset with string_view)
and should be slightly cheaper to instantiate.
We should consider using basic_string_view for C++17, C++20, and C++23
as well. This patch just conservatively changes it for C++26 to match
the working draft. It's conceivable that a program-defined
specialization of basic_string<_CharT> or basic_string_view<_CharT> will
observe a difference and be affected by this change.
libstdc++-v3/ChangeLog:
* include/std/bitset (__bitset::__string) [__cpp_lib_bitset]:
Change alias to refer to basic_string_view instead.
Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>
Add a bitset constructor from string_view, per P2697. Fix existing
tests that would fail to detect incorrect exception behavior.
Argument checks that result in exceptions guarded by "#if HOSTED"
are made unguarded because the functions called to throw just call
terminate() in free-standing builds. Improve readability in Doxygen
comments. Generalize a private member argument-checking function
to work with string and string_view without mentioning either,
obviating need for guards.
The version.h symbol is not "hosted" because string_view, though
not specified to be available in free-standing builds, is defined
there and the feature is useful there.
libstdc++-v3/ChangeLog:
PR libstdc++/119742
* include/bits/version.def: Add preprocessor symbol.
* include/bits/version.h: Add preprocessor symbol.
* include/std/bitset: Add constructor.
* testsuite/20_util/bitset/cons/1.cc: Fix.
* testsuite/20_util/bitset/cons/6282.cc: Fix.
* testsuite/20_util/bitset/cons/string_view.cc: Test new ctor.
* testsuite/20_util/bitset/cons/string_view_wide.cc: Test new ctor.
The standard says this constructor should be private. LWG 4141 proposes
to remove it entirely. We still need it, but it doesn't need to be
public.
For std::bitset the default constructor is already private (and never
even defined) but there's a non-standard constructor that's public, but
doesn't need to be.
libstdc++-v3/ChangeLog:
PR libstdc++/115098
* include/bits/stl_bvector.h (_Bit_reference): Make default
constructor private. Declare vector and bit iterators as
friends.
* include/std/bitset (bitset::reference): Make constructor and
data members private.
* testsuite/20_util/bitset/115098.cc: New test.
* testsuite/23_containers/vector/bool/115098.cc: New test.
As noted in the PR the compiler doesn't seem able to do this on its own,
so we get better code at all optimization levels by using memcmp.
libstdc++-v3/ChangeLog:
PR libstdc++/113807
* include/std/bitset (bitset::_M_is_equal()): Use memcmp to
optimize operator==.
The unused bits in the high word are already zero before this operation.
Shifting the used bits to the right cannot affect the unused bits, so we
don't need to sanitize them.
libstdc++-v3/ChangeLog:
PR libstdc++/113806
* include/std/bitset (bitset::operator>>=): Remove redundant
call to _M_do_sanitize.
As pointed out in the PR we already do this for reset().
libstdc++-v3/ChangeLog:
PR libstdc++/113807
* include/std/bitset (bitset::set()): Use memset instead of a
loop over the individual words.
This shift only happens if the unsigned long long type is wider than
unsigned long but the compiler warns when it sees the shift, without
caring if it's reachable.
Use the preprocessor to compare the sizes and just reuse _M_to_ulong()
if sizeof(long) == sizeof(long long).
libstdc++-v3/ChangeLog:
* include/std/bitset (_Base_bitset::_M_do_to_ullong): Avoid
-Wshift-count-overflow warning.
The use of alloca in a constructor is wrong, because the memory is gone
after the constructor returns, and will be overwritten by a subsequent
function call. This didn't show up in testing because function inlining
alters the stack usage.
libstdc++-v3/ChangeLog:
PR libstdc++/108214
* include/std/bitset (operator>>): Use alloca in the right
scope, not in a constructor.
* testsuite/20_util/bitset/io/input.cc: Check case from PR.
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.
The std::bitset constructor from a character string is specified in
terms of std::basic_string and std::char_traits, but doesn't need to be.
This makes it available for freestanding.
libstdc++-v3/ChangeLog:
* include/std/bitset (bitset(const C*, size_type n, C, C))
[!_GLIBCXX_HOSTED]: Remove std::basic_string dependency.
(_M_copy_from_ptr) [!_GLIBCXX_HOSTED]: Abort instead of
throwing.
We can improve performance by using a char buffer instead of
basic_string. The loop bound already means we can't overflow the buffer,
and we don't need to keep writing a null character after every character
written to the buffer.
We could just use basic_string::resize(N) to zero-init the whole string,
then overwrite those chars. But that zero-init of all N chars would be
wasted in the case where we are writing to a bitset<N> with large N, but
only end up extracting one or two chars from the stream.
With this change we just use buffer of uninitialized chars. For a
small-ish bitset (currently <= 256) we can improve performance further
by using alloca instead of the heap.
libstdc++-v3/ChangeLog:
* include/std/bitset (operator>>): Use a simple buffer instead
of std::basic_string.
This makes _M_copy_from_ptr, _M_copy_from_string and _M_copy_to_string
private, and declares operator<< and operator>> as friends.
Also remove the historical _M_copy_from_string and _M_copy_to_string
overloads. Those were used before DR 396 was implemented but are
not needed now. There are no tests or docs describing them, so I don't
think we intend to support them as extensions.
libstdc++-v3/ChangeLog:
* include/std/bitset (_M_copy_from_ptr, _M_copy_from_string)
(_M_copy_to_string): Change access to private.
(_M_copy_from_string(const basic_string&, size_t, size_t)):
Remove.
(_M_copy_to_string(const basic_string&)): Remove.
Don't bother trying to copy any characters for bitset<0>.
libstdc++-v3/ChangeLog:
* include/std/bitset (operator>>): Do not copy for N==0.
* testsuite/20_util/bitset/io/input.cc: Add comment.
This makes to_string approximately twice as fast at any optimization
level. Instead of iterating through every bit, jump straight to the next
bit that is set, by using _Find_first and _Find_next.
libstdc++-v3/ChangeLog:
* include/std/bitset (bitset::_M_copy_to_string): Find set bits
instead of iterating over individual bits.
Also add _GLIBCXX_HOSTED checks to simplify making <bitset>
freestanding in the near future.
libstdc++-v3/ChangeLog:
* include/std/bitset (bitset): Add constexpr for C++23. Guard
members using std::string with _GLIBCXX_HOSTED.
* include/std/version (__cpp_lib_constexpr_bitset): Define.
* testsuite/20_util/bitset/access/constexpr.cc: New test.
* testsuite/20_util/bitset/cons/constexpr_c++23.cc: New test.
* testsuite/20_util/bitset/count/constexpr.cc: New test.
* testsuite/20_util/bitset/ext/constexpr.cc: New test.
* testsuite/20_util/bitset/operations/constexpr_c++23.cc: New test.
* testsuite/20_util/bitset/version.cc: New test.
Some more C++20 changes from P1614R2, "The Mothership has Landed".
This removes all redundant equality and inequality operators in the
Utilities clause, as they can be synthesized from the remaining equality
operators.
It also removes the single redundant operator in the Localization
clause, because it didn't seem worth doing in a separate commit.
* include/bits/allocator.h (operator!=): Do not define for C++20.
* include/bits/locale_classes.h (operator!=): Likewise.
* include/bits/std_function.h (operator==(nullptr_t, const function&))
(operator!=(const function&, nullptr_t))
(operator!=(nullptr_t, const function&)): Likewise.
* include/ext/bitmap_allocator.h (operator!=): Likewise.
* include/ext/debug_allocator.h (operator!=): Likewise.
* include/ext/extptr_allocator.h (operator!=): Likewise.
* include/ext/malloc_allocator.h (operator!=): Likewise.
* include/ext/mt_allocator.h (operator!=): Likewise.
* include/ext/new_allocator.h (operator!=): Likewise.
* include/ext/pool_allocator.h (operator!=): Likewise.
* include/ext/throw_allocator.h (operator!=): Likewise.
* include/std/bitset (bitset::operator!=): Likewise.
* include/std/memory_resource (operator!=): Likewise.
* include/std/scoped_allocator (operator!=): Likewise.
Nathan Myers