The intent of these particular functions, since their introduction, was
to NOT be inlinable.
However, the mechanism by which this was accomplished was non-obvious,
and stopped working when string is compiled for C++20.
A longstanding behavior specified by the C++ standard is that
instantiation of the body of a template function is suppressed by an
extern template declaration -- unless the function is explicitly marked
either constexpr or inline. Of course, if the body is not instantiated,
then it cannot possibly be inlined, and thus all the functions listed in
libcxx/include/__string/extern_template_lists.h were uninlineable.
But, in C++20 mode, string functions were annotated constexpr, which
means they _are_ instantiated, and do become inlineable. And, in fact,
they do get inlined, which has caused noticeable binary-size growth for
users.
For example, in C++17,
`std::string f(std::string *in) { return *in; }`
does not inline the copy-constructor call, and instead generates a call
to the exported function defined in the libc++ shared library.
I think we probably don't want to mark all functions that are currently
in the extern template list as noinline, as many of them really are
reasonable inlining candidates. Thus, I've restricted this change to
only the few functions that were clearly intended to be outlined.
See commits like b019c5c0372eb08800327efb5e7955ce918b75d1 (and some
others like it) for background, in which functions were removed from the
extern template list in the unstable ABI in order to allow the
short-string case to be inlined, while moving the long-string case to a
separate function, added to the extern template list.
If we know that index is larger than SSO size, we know that we can't be
in SSO case, and should access the pointer. This removes extra check
from operator[] for inputs known at compile time to be larger than SSO.
This allows smaller allocations to occur, closer to the actual
std::string's required size. This is particularly effective in
decreasing the allocation size upon initial construction (where
__recommend is called to determine the size).
Although the memory savings per-string are never more than 8 bytes per
string initially, this quickly adds up. And has lead to not insigficant
memory savings at Google.
Unfortunately, this change is ABI breaking because it changes the value
returned by max_size. So it has to be guarded.
Previously, libcxx forced all strings created during constant evaluation
to point to allocated memory. That was done due to implementation
difficultites, but it turns out not to be necessary. This patch permits
the use of SSO strings during constant evaluation, and also simplifies
the implementation.
This does have a downside in terms of enabling users to accidentally
write non-portable code, however, which I've documented in
UsingLibcxx.rst.
In particular, whether `constinit std::string x = "...";` will
successfully compile now depends on whether the string is smaller than
the SSO capacity -- in libc++, up to 22 bytes on 64-bit platforms, and
up to 10 bytes on 32-bit platforms. By comparison, libstdc++ and MSVC
have an SSO capacity of 15 bytes, except that in libstdc++,
constant-initialized strings cannot be used as function-locals because
the object contains a pointer to itself.
Closes#68434
Previously, assignment to a std::basic_string type with a _custom_
allocator could under certain conditions attempt to interpret part of
the target string's "short" string-content as if it was a "long" data
pointer, and attempt to deallocate a garbage value.
This is a serious bug, but code in which it might happen is rare. It
required:
1. the basic_string must be using a custom allocator type which sets the
propagate_on_container_copy_assignment trait to true (thus, it does not
affect the default allocator, nor most custom allocators).
2. the allocator for the target string must compare not equal to the
allocator for the source string (many allocators always compare equal).
3. the source of the copy must currently contain a "long" string, and
the assignment-target must currently contain a "short" string.
Finally, the issue would've typically been innocuous when the bytes
misinterpreted as a pointer were all zero, as deallocating a nullptr is
typically a no-op. This is why existing test cases did not exhibit an
issue: they were all zero-length strings, which do not have data in the
bytes interpreted as a pointer.
This commit deprecates `std::basic_string::__grow_by`, which is part of ABIv1. The function is replaced by `std::basic_string:__grow_by_without_replace`, which is not part of ABI.
- The original function `__grow_by` is deprecated because it does not set the string size, therefore it may not update the size when the size is changed, and it may also not set the size at all when the string was short initially. This leads to unpredictable size value. It is not removed or changed to avoid breaking the ABI.
- The commit adds `_LIBCPP_HIDE_FROM_ABI` guarded by `_LIBCPP_ABI_VERSION >= 2` to `__grow_by`. This allows the function to be used in the dylib in ABIv1 without raising the `[abi:v170000]` error and removes it from future ABIs. `_LIBCPP_HIDE_FROM_ABI_AFTER_V1` cannot be used.
- Additionally, `__grow_by` has been removed from `_LIBCPP_STRING_UNSTABLE_EXTERN_TEMPLATE_LIST` in `libcxx/include/__string/extern_template_lists.h`.
This bugfix is necessary to implement string ASan annotations, because it mitigates the problems encountered in D132769.
Reviewed By: ldionne, #libc, philnik
Differential Revision: https://reviews.llvm.org/D148693
Remove spaces between operator"" and identifier to suppress
-Wdeprecated-literal-operator, and between operator and ""
like how they are written in [string.view.literals] and [basic.string.literals].
Differential Revision: https://reviews.llvm.org/D155200
- add the `from_range_t` constructors and the related deduction guides;
- add the `insert_range`/`assign_range`/etc. member functions.
(Note: this patch is split from https://reviews.llvm.org/D142335)
Differential Revision: https://reviews.llvm.org/D149832
Replace most uses of `_LIBCPP_ASSERT` with
`_LIBCPP_ASSERT_UNCATEGORIZED`.
This is done as a prerequisite to introducing hardened mode to libc++.
The idea is to make enabling assertions an opt-in with (somewhat)
fine-grained controls over which categories of assertions are enabled.
The vast majority of assertions are currently uncategorized; the new
macro will allow turning on `_LIBCPP_ASSERT` (the underlying mechanism
for all kinds of assertions) without enabling all the uncategorized
assertions (in the future; this patch preserves the current behavior).
Differential Revision: https://reviews.llvm.org/D153816
These macros are always defined identically, so we can simplify the code a bit by merging them.
Reviewed By: ldionne, #libc
Spies: libcxx-commits, krytarowski, smeenai
Differential Revision: https://reviews.llvm.org/D152652
This checks whether a pointer is within a range, even during constant evaluation. This allows running optimized code paths during constant evaluation, instead of falling back to the general-purpose implementation all the time. This is also a central place for comparing unrelated pointers, which is technically UB.
Reviewed By: ldionne, #libc
Spies: libcxx-commits
Differential Revision: https://reviews.llvm.org/D143327
During the ISO C++ Committee meeting plenary session the C++23 Standard
has been voted as technical complete.
This updates the reference to c++2b to c++23 and updates the __cplusplus
macro.
Note since we use clang-tidy 16 a small work-around is needed. Clang
knows -std=c++23 but clang-tidy not so for now force the lit compiler
flag to use -std=c++2b instead of -std=c++23.
Reviewed By: #libc, philnik, jloser, ldionne
Differential Revision: https://reviews.llvm.org/D150795
We plan to add concepts for checking that iterators actually provide what they claim to. This is to avoid people thinking that these type traits actually check the iterator requirements in more detail.
Reviewed By: ldionne, #libc
Spies: Mordante, libcxx-commits, wenlei
Differential Revision: https://reviews.llvm.org/D150801
Makes sure the formatter for the vector<bool>::reference is enabled
when only the header <vector> is included. Before this change it
required <vector> and <format> to be included. This violated the
requirements in the Standard.
Fixes: https://llvm.org/PR61314
Reviewed By: #libc, ldionne
Differential Revision: https://reviews.llvm.org/D149543
We changed the `abort` calls when trying to throw exceptions in `-fno-exceptions` mode to `__verbose_abort` calls, which removes the dependency in most files.
Reviewed By: ldionne, #libc
Spies: dim, emaste, mikhail.ramalho, smeenai, libcxx-commits
Differential Revision: https://reviews.llvm.org/D146076
This allows the compiler to inline the constructors.
Reviewed By: ldionne, #libc
Spies: mikhail.ramalho, libcxx-commits
Differential Revision: https://reviews.llvm.org/D144580
This changes all `__enable_if`s inside `<string>` to a common pattern. Specifically, it's always inside the `template <>` and uses the `, int> = 0` style.
Reviewed By: ldionne, #libc
Spies: mikhail.ramalho, EricWF, libcxx-commits
Differential Revision: https://reviews.llvm.org/D144568
This patch also updates the moved code to the new style (i.e. formatted, replaced marcos and typedefs)
Reviewed By: ldionne, #libc
Spies: arichardson, libcxx-commits
Differential Revision: https://reviews.llvm.org/D145095
Avoids using operator& in basic_string since an evil char-like type can
hijack this operator. Added some more evil operators, this found a place
where equality was compared directly and not via the traits.
This adds a helper test string. This is now only used in a few tests,
but the intention is to use this in more tests for basic_string.
Reviewed By: #libc, ldionne
Differential Revision: https://reviews.llvm.org/D145257
Other macros that disable parts of the library are named `_LIBCPP_HAS_NO_WHATEVER`.
Reviewed By: ldionne, Mordante, #libc
Spies: libcxx-commits, smeenai
Differential Revision: https://reviews.llvm.org/D143163
This change is almost fully mechanical. The only interesting change is in `generate_feature_test_macro_components.py` to generate `_LIBCPP_STD_VER >=` instead. To avoid churn in the git-blame this commit should be added to the `.git-blame-ignore-revs` once committed.
Reviewed By: ldionne, var-const, #libc
Spies: jloser, libcxx-commits, arichardson, arphaman, wenlei
Differential Revision: https://reviews.llvm.org/D143962
This prepares the terrain for introducing a new type of bounded iterator
that can't be constructed like __wrap_iter. This reverts part of the
changes made to std::vector in 4eab04f84.
Differential Revision: https://reviews.llvm.org/D138036
I am starting to granularize debug-mode checks so they can be controlled
more individually. The goal is for vendors to eventually be able to select
which categories of checks they want embedded in their configuration of
the library with more granularity.
Note that this patch is a bit weird on its own because it does not touch
any of the containers that implement iterator bounds checking through the
__dereferenceable check of the legacy debug mode. However, I added TODOs
to string and vector to change that.
Differential Revision: https://reviews.llvm.org/D138033
This removes a lot of boilerplate.
Reviewed By: ldionne, #libc, EricWF
Spies: EricWF, libcxx-commits
Differential Revision: https://reviews.llvm.org/D137025
This doesn't affect our ABI because `std::string::substr()` isn't in the dylib and the mangling of `substr() const` and `substr() const&` are different.
Reviewed By: ldionne, Mordante, var-const, avogelsgesang, #libc
Spies: arphaman, huixie90, libcxx-commits
Differential Revision: https://reviews.llvm.org/D131668
We currently define the preferred names in multiple places. `basic_string` and `basic_string_view` also have a lot of aliases, which makes the declarations quite long. So let's only add the preferred names in forward-declaring headers to make the implementation more readable and have all the preferred names in one place.
Reviewed By: ldionne
Spies: EricWF, krytarowski, libcxx-commits
Differential Revision: https://reviews.llvm.org/D135824
This patch is the rebase and squash of three earlier patches.
It supersedes all three of them.
- D47111: experimental monotonic_buffer_resource.
- D47358: experimental pool resources.
- D47360: Copy std::experimental::pmr to std::pmr.
The significant difference between this patch and the-sum-of-those-three
is that this patch does not add `std::experimental::pmr::monotonic_buffer_resource`
and so on. This patch simply adds the C++17 standard facilities, and
leaves the `std::experimental` namespace entirely alone.
Differential Revision: https://reviews.llvm.org/D89057
This removes a lot of boilerplate code.
Reviewed By: ldionne, #libc
Spies: EricWF, libcxx-commits
Differential Revision: https://reviews.llvm.org/D128081
For some reason `operator""s(const char8_t*, size_t)` was marked `noexcept`. Remove it and add regression tests.
Reviewed By: ldionne, huixie90, #libc
Spies: libcxx-commits
Differential Revision: https://reviews.llvm.org/D132340
This defines a new policy for removal of transitive includes.
The goal of the policy it to make it relatively easy to remove
headers when needed, but avoid breaking developers using and
vendors shipping libc++.
The method used is to guard transitive includes based on the
C++ language version. For the upcoming C++23 we can remove
headers when we want, but for other language versions we try
to keep it to a minimum.
In this code the transitive include of `<chrono>` is removed
since D128577 introduces a header cycle between `<format>`
and `<chrono>`. This cycle is indirectly required by the
Standard. Our cycle dependency tool basically is a grep based
tool, so it needs some hints to ignore cycles. With the input
of our transitive include tests we can create a better tool.
However that's out of the scope of this patch.
Note the flag `_LIBCPP_REMOVE_TRANSITIVE_INCLUDES` remains
unchanged. So users can still opt-out of transitives includes
entirely.
Reviewed By: #libc, ldionne, philnik
Differential Revision: https://reviews.llvm.org/D132284
