This patch introduces a new trait to represent whether a type is
trivially
relocatable, and uses that trait to optimize the growth of a std::vector
of trivially relocatable objects.
```
--------------------------------------------------
Benchmark old new
--------------------------------------------------
bm_grow<int> 1354 ns 1301 ns
bm_grow<std::string> 5584 ns 3370 ns
bm_grow<std::unique_ptr<int>> 3506 ns 1994 ns
bm_grow<std::deque<int>> 27114 ns 27209 ns
```
This also changes to order of moving and destroying the objects when
growing the vector. This should not affect our conformance.
This patch has quite a bit of history. First, it must be noted that the
Standard only specifies specializations of char_traits for char,
char8_t, char16_t, char32_t and wchar_t. However, before this patch, we
would provide a base template that accepted anything, and as a result
code like `std::basic_string<long long>` would compile but nobody knows
what it really does. It basically compiles by accident.
We marked the base template as deprecated in LLVM 15 or 16 and were
planning on removing it in LLVM 17, which we did in e30a148b098d.
However, it turned out that the deprecation warning had never been
visible in user code since Clang did not surface that warning from
system headers. As a result, this caught people by surprise and we
decided to reintroduce the base template in LLVM 17 in cce062d226ba.
Since then, #70353 changed Clang so that such deprecation warnings would
be visible from user code. Hence, this patch closes the loop and removes
the deprecated specializations.
The <__threading_support> header is a huge beast and it's really
difficult to navigate. I find myself struggling to find what I want
every time I have to open it, and I've been considering splitting it up
for years for that reason.
This patch aims not to contain any functional change. The various
implementations of the threading base are simply moved to separate
headers and then the individual headers are simplified in mechanical
ways. For example, we used to have redundant declarations of all the
functions at the top of `__threading_support`, and those are removed
since they are not needed anymore. The various #ifdefs are also
simplified and removed when they become unnecessary.
Finally, this patch adds documentation for the API we expect from any
threading implementation.
This will make it easier for folks who have patches that are not
targeting LLVM 18 -- they can write the release notes in the LLVM 19
release notes immediately.
Unconditionally change std::string's alignment to 8.
This change saves memory by providing the allocator more freedom to
allocate the most
efficient size class by dropping the alignment requirements for
std::string's
pointer from 16 to 8. This changes the output of std::string::max_size,
which makes it ABI breaking.
That said, the discussion concluded that we don't care about this ABI
break. and would like this change enabled universally.
The ABI break isn't one of layout or "class size", but rather the value
of "max_size()" changes, which in turn changes whether `std::bad_alloc`
or `std::length_error` is thrown for large allocations.
This change is the child of PR #68807, which enabled the change behind
an ABI flag.
In D144319, Clang tried to land a change that would cause some functions
that are not supposed to return nullptr to optimize better. As reported
in https://reviews.llvm.org/D144319#4203982, libc++ started seeing
failures in its CI shortly after this change was landed.
As explained in D146379, the reason for these failures is that libc++'s
throwing `operator new` can in fact return nullptr when compiled with
exceptions disabled. However, this contradicts the Standard, which
clearly says that the throwing version of `operator new(size_t)` should
never return nullptr. This is actually a long standing issue. I've
previously seen a case where LTO would optimize incorrectly based on the
assumption that `operator new` doesn't return nullptr, an assumption
that was violated in that case because libc++.dylib was compiled with
-fno-exceptions.
Unfortunately, fixing this is kind of tricky. The Standard has a few
requirements for the allocation functions, some of which are impossible
to satisfy under -fno-exceptions:
1. `operator new(size_t)` must never return nullptr
2. `operator new(size_t, nothrow_t)` must call the throwing version and
return nullptr on failure to allocate
3. We can't throw exceptions when compiled with -fno-exceptions
In the case where exceptions are enabled, things work nicely.
`new(size_t)` throws and `new(size_t, nothrow_t)` uses a try-catch to
return nullptr. However, when compiling the library with
-fno-exceptions, we can't throw an exception from `new(size_t)`, and we
can't catch anything from `new(size_t, nothrow_t)`. The only thing we
can do from `new(size_t)` is actually abort the program, which does not
make it possible for `new(size_t, nothrow_t)` to catch something and
return nullptr.
This patch makes the following changes:
1. When compiled with -fno-exceptions, the throwing version of `operator
new` will now abort on failure instead of returning nullptr on failure.
This resolves the issue that the compiler could mis-compile based on the
assumption that nullptr is never returned. This constitutes an API and
ABI breaking change for folks compiling the library with -fno-exceptions
(which is not the general public, who merely uses libc++ headers but use
a shared library that has already been compiled). This should mostly
impact vendors and other folks who compile libc++.dylib themselves.
2. When the library is compiled with -fexceptions, the nothrow version
of `operator new` has no change. When the library is compiled with
-fno-exceptions, the nothrow version of `operator new` will now check
whether the throwing version of `operator new` has been overridden. If
it has not been overridden, then it will use an implementation
equivalent to that of the throwing `operator new`, except it will return
nullptr on failure to allocate (instead of terminating). However, if the
throwing `operator new` has been overridden, it is now an error NOT to
also override the nothrow `operator new`. Indeed, there is no way for us
to implement a valid nothrow `operator new` without knowing the exact
implementation of the throwing version.
In summary, this change will impact people who fall into the following
intersection of conditions:
- They use the libc++ shared/static library built with `-fno-exceptions`
- They do not override `operator new(..., std::nothrow_t)`
- They override `operator new(...)` (the throwing version)
- They use `operator new(..., std::nothrow_t)`
We believe this represents a small number of people.
Fixes#60129
rdar://103958777
Differential Revision: https://reviews.llvm.org/D150610
This reverts commit 7d9b5aa65b09126031e1c2903605a7d34aea4bc1 since
std/utilities/format/format.arguments/format.arg/visit.return_type.pass.cpp
is failing on Windows when building with Clang-cl.
This patch implements __cxa_init_primary_exception, an extension to the
Itanium C++ ABI. This extension is already present in both libsupc++ and
libcxxrt. This patch also starts making use of this function in
std::make_exception_ptr: instead of going through a full throw/catch
cycle, we are now able to initialize an exception directly, thus making
std::make_exception_ptr around 30x faster.
In LLVM 17, we switched to numbered RST files for release notes, which
makes it easier to deal with cherry-picks around release points. However,
we stopped publishing `libcxx/docs/ReleaseNotes.html`, which was
referenced by external sites.
This patch ensures that we keep publishing `ReleaseNotes.html` by simply
including the versioned RST file in the unversioned RST file.
Fixes#77955
Currently std::expected can have some padding bytes in its tail due to
[[no_unique_address]]. Those padding bytes can be used by other objects.
For example, in the current implementation:
sizeof(std::expected<std::optional<int>, bool>) ==
sizeof(std::expected<std::expected<std::optional<int>, bool>, bool>)
As a result, the data layout of an
std::expected<std::expected<std::optional<int>, bool>, bool>
can look like this:
+-- optional "has value" flag
| +--padding
/---int---\ | |
00 00 00 00 01 00 00 00
| |
| +- "outer" expected "has value" flag
|
+- expected "has value" flag
This is problematic because `emplace()`ing the "inner" expected can not
only overwrite the "inner" expected "has value" flag (issue #68552) but
also the tail padding where other objects might live.
This patch fixes the problem by ensuring that std::expected has no tail
padding, which is achieved by conditional usage of [[no_unique_address]]
based on the tail padding that this would create.
This is an ABI breaking change because the following property changes:
sizeof(std::expected<std::optional<int>, bool>) <
sizeof(std::expected<std::expected<std::optional<int>, bool>, bool>)
Before the change, this relation didn't hold. After the change, the relation
does hold, which means that the size of std::expected in these cases increases
after this patch. The data layout will change in the following cases where
tail padding can be reused by other objects:
class foo : std::expected<std::optional<int>, bool> {
bool b;
};
or using [[no_unique_address]]:
struct foo {
[[no_unique_address]] std::expected<std::optional<int>, bool> e;
bool b;
};
The vendor communication is handled in #70820.
Fixes: #70494
Co-authored-by: philnik777 <nikolasklauser@berlin.de>
Co-authored-by: Louis Dionne <ldionne.2@gmail.com>
Installs the source files of the experimental libc++ modules. These
source files (.cppm) are used by the Clang to build the std and
std.compat modules.
The design of this patch is based on a discussing in SG-15 on
12.12.2023. (SG-15 is the ISO C++ Tooling study group):
- The modules are installed at a location, that is not known to build
systems and compilers.
- Next to the library there will be a module manifest json file.
This json file contains the information to build the module from the
libraries sources. This information includes the location where the
sources are installed. @ruoso supplied the specification of this json
file.
- If possible, the compiler has an option to give the location of the
module manifest file
(https://github.com/llvm/llvm-project/pull/76451).
Currently there is no build system support, but it expected to be added
in the future.
Fixes: https://github.com/llvm/llvm-project/issues/73089
Revert "Revert #76246 and #76083"
This reverts commit 5c150e7eeba9db13cc65b329b3c3537b613ae61d.
Adds a small fix that should properly disable the tests on Windows.
Unfortunately the original poster has not provided feedback and the
original patch did not fail in the LLVM CI infrastructure.
Modules are known to fail on Windows due to non compliance of the
C library. Currently not having this patch prevents testing on other
platforms.
CMake officially supports binary directory variable of installed
dependency using `FetchContent`. According to the current documentation,
it fetches `std` module and use its binary directory as hardcoded
string, `${CMAKE_BINARY_DIR}/_deps/std-build`, however it can be
replaced with `${std_BINARY_DIR}`.
Reference: https://cmake.org/cmake/help/latest/module/FetchContent.html
In the hardening modes that can be used in production (`fast` and
`extensive`), make a failed assertion invoke a trap instruction rather
than calling verbose abort. In the debug mode, still keep calling
verbose abort to provide a better user experience and to allow us to
keep our existing testing infrastructure for verifying assertion
messages. Since the debug mode by definition enables all assertions, we
can be sure that we still check all the assertion messages in the
library when running the test suite in the debug mode.
The main motivation to use trapping in production is to achieve better
code generation and reduce the binary size penalty. This way, the
assertion handler can compile to a single instruction, whereas the
existing mechanism with verbose abort results in generating a function
call that in general cannot be optimized away (made worse by the fact
that it's a variadic function, imposing an additional penalty). See the
[RFC](https://discourse.llvm.org/t/rfc-hardening-in-libc/73925) for more
details. Note that this mechanism can now be completely [overridden at
CMake configuration
time](https://github.com/llvm/llvm-project/pull/77883).
This patch also significantly refactors `check_assertion.h` and expands
its test coverage. The main changes:
- when overriding `verbose_abort`, don't do matching inside the function
-- just print the error message to `stderr`. This removes the need to
set a global matcher and allows to do matching in the parent process
after the child finishes;
- remove unused logic for matching source locations and for using
wildcards;
- make matchers simple functors;
- introduce `DeathTestResult` that keeps data about the test run,
primarily to make it easier to test.
In addition to the refactoring, `check_assertion.h` can now recognize
when a process exits due to a trap.
These cause test build failures on Windows.
This reverts the following commits:
57ca74843586c9a93c425036c5538aae0a2cfa60
d06ae33ec32122bb526fb35025c1f0cf979f1090
Previously there were two ways to override the verbose abort function
which gets called when a hardening assertion is triggered:
- compile-time: define the `_LIBCPP_VERBOSE_ABORT` macro;
- link-time: provide a definition of `__libcpp_verbose_abort` function.
This patch adds a new configure-time approach: the vendor can provide
a path to a custom header file which will get copied into the build by
CMake and included by the library. The header must provide a definition
of the
`_LIBCPP_ASSERTION_HANDLER` macro which is what will get called should
a hardening assertion fail. As of this patch, overriding
`_LIBCPP_VERBOSE_ABORT` will still work, but the previous mechanisms
will be effectively removed in a follow-up patch, making the
configure-time mechanism the sole way of overriding the default handler.
Note that `_LIBCPP_ASSERTION_HANDLER` only gets invoked when a hardening
assertion fails. It does not affect other cases where
`_LIBCPP_VERBOSE_ABORT` is currently used (e.g. when an exception is
thrown in the `-fno-exceptions` mode).
The library provides a default version of the custom header file that
will get used if it's not overridden by the vendor. That allows us to
always test the override mechanism and reduces the difference in
configuration between the pristine version of the library and
a platform-specific version.
This adds a new module test infrastructure. This requires tagging tests
using modules. The test runner uses this information to determine the
compiler flags needed to build and use the module.
Currently modules are build per test, which allows testing them for
tests with ADDITIONAL_COMPILE_FLAGS. At the moment only 4 tests use
modules. Therefore the performance penalty is not measurable. If in the
future more tests use modules it would be good to measure the overhead
and determine whether it's acceptable.
This removes the entire modules testing infrastructure.
The current infrastructure uses CMake to generate the std and std.compat
module. This requires quite a bit of plumbing and uses CMake. Since
CMake introduced module support in CMake 3.26, modules have a higher
CMake requirement than the rest of the LLVM project. (The LLVM project
requires 3.20.) The main motivation for this approach was how libc++
generated its modules. Every header had its own module partition. This
was changed to improve performance and now only two modules remain. The
code to build these can be manually crafted.
A followup patch will reenable testing modules, using a different
approach.
We discussed the removal of these enable-all macros in the libc++
monthly meeting and we agreed that we should deprecate these macros in
LLVM 18, and then remove them in LLVM 19 since they can silently enable
deprecated features that are implemented after the first release of the
macro.
This patch does the first part of this -- it deprecates the macro.
Note that the file
test/libcxx/depr/enable_removed_cpp20_features.compile.pass.cpp
does not exist so this file is not adapted. Since the feature is
deprecated and slated for removal soon the missing test is not
implemented.
Partly addresses: https://github.com/llvm/llvm-project/issues/75976
---------
Co-authored-by: Louis Dionne <ldionne.2@gmail.com>
The old notes are kept to make it easier to backport changes to the
release branch. There are no LLVM-17 releases expected and this
documentation should not be available in the LLVM-18 release.
Note after branching LLVM-18 both LLVM-18 and LLVM-19 release notes
should be available.
GCC 13 is the latest GCC release and tested in the libc++ CI for several
month. According to our policy we only support the latest version,
update the documentation to the latest version.
As described in #69994, using the escape hatch makes us non-conforming
in C++20 due to incorrect constexpr-ness. It also leads to bad
diagnostics as reported by #63900. We discussed the issue in the libc++
monthly meeting and we agreed that we should deprecate the macro in LLVM
18, and then remove it in LLVM 19 since it causes too many problems.
This patch does the first part of this -- it deprecates the macro.
Fixes#69994Fixes#63900
Partially addresses #75975
I recently came across LIBCXXABI_USE_LLVM_UNWINDER and was surprised to
notice it was disabled by default. Since we build libunwind by default
and ship it in the LLVM toolchain, it would seem to make sense that
libc++ and libc++abi rely on libunwind for unwinding instead of using
the system-provided unwinding library (if any).
Most importantly, using the system unwinder implies that libc++abi is
ABI compatible with that system unwinder, which is not necessarily the
case. Hence, it makes a lot more sense to instead default to using the
known-to-be-compatible LLVM unwinder, and let vendors manually select a
different unwinder if desired.
As a follow-up change, we should probably apply the same default to
compiler-rt.
Differential Revision: https://reviews.llvm.org/D150897Fixes#77662
rdar://120801778
As a new contributor, I found it hard to find the documentation for the
meaning of the names of different tests and how those names translate to
Lit. This patch moves the documentation to the RST documentation we
publish on the website instead of leaving it in the source code only.
The current CI badge is currently in libc++ documentation. This does not
seem the right place:
- The typical location on GitHub is on the main README.
- The documentation is shipped as part of the release:
- This link does not work in off-line mode. Currently our documentation
works in off-line mode.
- The status in the release documentation does not reflect the status of
the shipped library. So users looking at it may see a red status and get
confused.
This moves the badge to the README.
As pointed out by @Zingam the paper was implemented in libc++ as an
extension. This patch does the bookkeeping. The inital release version
is based on historical release dates.
Completes:
- Add a conditional noexcept specification to std::apply
The macros were already updated
- __cpp_lib_string_view in 466df1718e41fe2fca6ce6bd98c01b18f42c05e4
- __cpp_lib_array_constexpr in 77b9abfc8e89ca627e4f9a1cc206bea131db6db1
Based on the dates of the commit and that
P0858 "Constexpr iterator requirements"
was completed in LLVM 12, set this issue as completed in the same
version.
Completes
- LWG3257 Missing feature testing macro update from P0858
