That way, local lit configuration files don't have to worry about
deep-copying the compiler instance of the test format, which is
arguably an implementation detail.
We pass the config to this method even though it is not used by the
current test format because this allows replacing the current test
format by other test formats that would require the config to add
new compile flags.
This reduces the complexity of our already complex global lit configuration,
and also avoids cluttering the compilation commands for all tests with
things that are only relevant to the filesystem tests.
Differential Revision: https://reviews.llvm.org/D76785
Previously, filesystem tests would require LIBCXX_FILESYSTEM_DYNAMIC_TEST_ROOT
to be present in the environment and to match the value provided when
compiling, as a macro. This has the problem that it only allows for the
filesystem tests to be run on the same machine they are created.
Instead, we create a temporary directory for each test. Technically,
this is tricky to do because we're relying on some of the code that
we're testing to do this. However, there's no other portable way of
creating temporary direcories in C++, so this is difficult to avoid.
Differential Revision: https://reviews.llvm.org/D76731
This re-commits cd7f9751c3, which was reverted in 12f6b024f9 because
it broke the LLVM `check-all` target. This commit addresses the underlying
issue by not setting the lit_config.recursiveExpansionLimit parameter of
the libc++ test suite, which is otherwise picked up by other test suites
in LLVM.
Once we've settled on a fix for the underlying issue with
lit_config.recursiveExpansionLimit, we can start using it
again in libc++, but for now we can just work around it.
We will soon start removing technical debt and sharing code between the
two directories, so this first step is meant to discover potential places
where the libraries are built outside of a monorepo layout. I imagine
this could happen as a remnant of the pre-monorepo setup.
This was discussed on the libcxx-dev mailing list and we got overall
consensus on the direction. All consumers of libc++ and libc++abi
should already be doing so through the monorepo, however it is
possible that we catch some stragglers with this patch, in which
case it may need to be reverted temporarily.
Differential Revision: https://reviews.llvm.org/D76102
This allows adding compilation flags for a single test, which can help
eliminate some .sh.cpp tests and some custom handling in the libc++
test format.
It also works around the issue that .sh.cpp substitutions are _not_
equivalent to the actual compiler command lines used to compile tests,
since the compiler flags can be modified in local lit configurations,
and substitutions are frozen at that point. For example using %{compile}
in a .sh.cpp test in the coroutines subdirectory will not include the
-fcoroutines-ts flag, which is added in the local lit config, because
the %{compile} substitution is created long before we add -fcoroutines-ts
to the compiler flags (in the lit.local.cfg for coroutines).
We've been meaning to remove those targets for a while, and the fix is
simple enough cause they're all just aliases to other targets.
This is a re-application of f383fb40b1, wich was reverted in 04d48111b
because the build bots had not been updated yet. The build bot configurations
have now been updated not to use the deprecated targets, and I verified
that they were using the non-deprecated targets, so we should be good
unless I missed a bot.
Differential Revision: https://reviews.llvm.org/D76104
This reverts commit cd7f9751c3 which has
unintended breakage to non-libcxx projects when using the documented way
of building LLVM. (See the Getting Started guide. I.e. one big CMake setup.)
Since lit supports expanding substitutions recursively, we can define
substitutions in terms of other substitutions. This allows us to simplify
how libc++ substitutions are defined.
This doesn't change the substitutions at all, it only makes them simpler
to define.
lit is not very clever when it performs substitution on RUN lines. It
simply looks for a match anywhere in the line (without tokenization)
and replaces it by the expansion. This means that a RUN line containing
e.g. `-verify-ignore-unexpected=note` wouod be expanded to
`-verify-ignore-unexpected=<substitution for not>e`, which is
surprising and nonsensical.
It also means that something like `%compile_module` could be expanded
to `<substitution-for-%compile>_module` or to the correct substitution,
depending on the order in which substitutions are evaluated by lit.
To avoid such problems, it is a good habit to delimit custom substitutions
with some token. This commit does that for all substitutions used in the
libc++ and libc++abi test suites.
Summary:
The gdb pretty printer misprints variables declared via
using declarations of the form:
namespace foo {
using string_view = std::string_view;
string_view bar;
}
This change fixes that, by deferring the decision to ignore
types not inside std until after desugaring.
Reviewers: #libc!
Subscribers: broadwaylamb, libcxx-commits
Tags: #libc
Differential Revision: https://reviews.llvm.org/D76816
This reverts commit a32b94c6c3.
The buildbot startup scripts need to run as root. The buildbot
worker should have already been running as a different account.
More investigation needed.
Forcing -Werror and other warnings means that the test suite isn't
actually testing what most people are seeing in their code -- it seems
better and less arbitrary to compile these tests as close as possible
to the compiler default instead.
Removing -Werror also means that we get to differentiate between
diagnostics that are errors and those that are warnings, which makes
the test suite more precise.
Differential Revision: https://reviews.llvm.org/D76311
We have several test directories whose names end in .spec. Ensure we
don't accidentally ignore them by removing a section of the .gitignore
that's irrelevant for libc++.
Differential Revision: https://reviews.llvm.org/D69195
Introduced by https://reviews.llvm.org/D72687. This condition can happen
when the tests are not being run at all, and we're only trying to generate
the libc++ headers.
Some tests do not fail at all when -verify is not supported, unless some
arbitrary warning flag is added to make them fail. We currently used
-Werror=unused-result to make them fail, but doing so makes the test
suite a lot more inscrutable. It seems better to just disable those
tests when -verify is not supported.
Differential Revision: https://reviews.llvm.org/D76256
It's hard to imagine someone using a recent version of libc++ with a
roughly 3 years old Clang. Since we're not testing libc++ with Clang 3.5
anyway, claiming support for it is somewhat of a lie.
Note that we don't test Clang 4 either, however I have no reason to bump
the requirement beyond Clang 4 at the moment, whereas removing Clang 3.5
allows simplifying the test suite.
Differential Revision: https://reviews.llvm.org/D76618
This reverts commit f383fb40b. It looks like several of our build bots
are still using the legacy target names, so we'll change those before
we commit this change again.
We've been meaning to remove those targets for a while, and the fix is
simple enough cause they're all just aliases to other targets.
There's no doubt this commit will break some CI systems, however the
fix is trivial.
Differential Revision: https://reviews.llvm.org/D76104
This commit rewrites/removes the docker files used to create
the libc++ buildbots.
The major changes in this patch are:
1. Delete Dockerfiles used to build compilers. These have moved to
github.com/efcs/compiler-images
2. Minimize the llvm-buildbot docker image. Instead of running the
buildbots from a committed docker image, the builders now build the
image on startup. This means changes to the docker file automatically
propogate to the builders (within ~24 hours without restart).
3. Version the compilers used by the builders. This means the bots
won't start failing because the apt.llvm.org clang package updated.
The current lit test suite doesn't really allow us to express that the
test should be disabled when testing the trunk variant of libc++, even
if we're running it on a supported macOS. Because of that, the test
is enabled when _LIBCPP_DISABLE_AVAILABILITY is defined, and the test
XPASSes.
Before this patch, the %run substitution did not contain the same
environment variables as normal `pass.cpp` tests. It also didn't
have the right working directory and the script wasn't aware of
potential file dependencies.
With this change, the combination of %build and %run in a .sh.cpp script
should match how pass.cpp tests are actually executed much more closely.
In C++03 mode, nullptr is defined by libc++, not the compiler so, we can't use __is_fundamental (because it will return false for nullptr).
Fixes: 5ade17e0ca
This patch updates <type_traits> to use builtin type traits whenever
possible to improve compile times.
Differential Revision: https://reviews.llvm.org/D67900
The current implementation of binomial_distribution is not guaranteed to
converge for certain extreme configurations of the engine and distribution.
This is due to a mistake in the implementation of the algorithm from the
given reference paper. The algorithm in the paper is guaranteed to
terminate but has redundant statements. The current implementation
simplified away the redundancy into a while loop, but it excludes the
return condition of the case where a good sample cannot be returned for
the particular sample being used from the uniform distribution, which is
what causes the infinite loop. This change guarantees termination by
recognizing that a good sample cannot be returned and returning 0 after
breaking the loop. This is also in contrast to the paper because the
return value as specified in the paper violates basic checks in at least
a subset of the extreme cases where the current implementation fails to
terminate. This default return value of 0 is satisfactory for the
extreme case known so far.
Since this is only meant to affect extreme cases where the algorithm
does not terminate anyways, the behavior is expected to remain exactly
the same for all non-extreme cases that have been terminating so far.
Fixes https://llvm.org/PR44847
Differential Revision: https://reviews.llvm.org/D74997
Summary:
The former are like:
libcxx/include/typeinfo:322:11: warning: definition of implicit copy constructor for 'bad_cast' is deprecated because it has a user-declared destructor [-Wdeprecated-copy-dtor]
virtual ~bad_cast() _NOEXCEPT;
^
libcxx/include/typeinfo:344:11: note: in implicit copy constructor for 'std::bad_cast' first required here
throw bad_cast();
^
Fix these by adding an explicitly defaulted copy constructor.
The latter are like:
libcxx/include/codecvt:105:37: warning: dynamic exception specifications are deprecated [-Wdeprecated-dynamic-exception-spec]
virtual int do_encoding() const throw();
^~~~~~~
Fix these by using the _NOEXCEPT macro instead.
Reviewers: EricWF, mclow.lists, ldionne, #libc
Reviewed By: EricWF, #libc
Subscribers: dexonsmith, libcxx-commits
Tags: #libc
Differential Revision: https://reviews.llvm.org/D76150
Summary:
Android's libc uses new/delete internally and these are counted, so
the counter needs to be reset to zero at the start of the test.
Reviewers: EricWF, mclow.lists, #libc, ldionne
Reviewed By: #libc, ldionne
Subscribers: dexonsmith, libcxx-commits
Tags: #libc
Differential Revision: https://reviews.llvm.org/D76091
The benchmarks are intended to be build with C++17 but the
CMAKE_CXX_STANDARD in the LLVM forces the build to use C++14 by default.
This fixes the issue by setting the CXX_STANDARD property of the benchmark
targets.
The CMake documentation is not clear whether this will use the C++1z
fallback for older compilers. So this may break the benchmarks if somebody
uses the benchmarks with pre C++17 compilers with the C++1z fallback.
Differential Revision: https://reviews.llvm.org/D75955
Summary: The return type modification has already been implemented in rL364840 and rL365290.
Reviewers: ldionne, mclow.lists, EricWF, #libc!
Reviewed By: ldionne
Subscribers: christof, dexonsmith, libcxx-commits
Tags: #libc
Differential Revision: https://reviews.llvm.org/D70275
Summary:
This is NFC. We only add additional information to the log.
Reviewers: EricWF, ldionne, mclow.lists
Reviewed By: ldionne
Subscribers: kristof.beyls, dexonsmith, danielkiss, mgorny, ldionne, libcxx-commits
Tags: #libc
Differential Revision: https://reviews.llvm.org/D75991
Due to Clang bug http://llvm.org/PR45151, deprecated attributes are not
picked up on partial specializations. This patch instead applies it to
the first declaration of std::function itself.
Summary:
This is a recommit of https://reviews.llvm.org/D73223 where the added function accidentally ended up inside an idef block.
This change splits the copy constructor up inlining short initialization, and explicitly outlining long initialization into __init_copy_ctor_external() which is the externally instantiated slow path.
For unstable ABI, this has the following changes:
remove basic_string(const basic_string&)
remove basic_string(const basic_string&, const Allocator&)
add __init_copy_ctor_external(const value_type*, size_type)
Quick local benchmark for Copy:
Master
```
---------------------------------------------------------------
Benchmark Time CPU Iterations
---------------------------------------------------------------
BM_StringCopy_Empty 3.50 ns 3.51 ns 199326720
BM_StringCopy_Small 3.50 ns 3.51 ns 199510016
BM_StringCopy_Large 15.7 ns 15.7 ns 45230080
BM_StringCopy_Huge 1503 ns 1503 ns 464896
```
With this change
```
---------------------------------------------------------------
Benchmark Time CPU Iterations
---------------------------------------------------------------
BM_StringCopy_Empty 1.99 ns 2.00 ns 356471808
BM_StringCopy_Small 3.29 ns 3.30 ns 203425792
BM_StringCopy_Large 13.3 ns 13.3 ns 52948992
BM_StringCopy_Huge 1472 ns 1472 ns 475136
```
Subscribers: libcxx-commits
Tags: #libc
Differential Revision: https://reviews.llvm.org/D75639
They need to appear before any member functions are ODR used, because
they change the visibility of many of these functions and otherwise
they could end up with hidden visibility in the DSO.
The goal of the test was only to check that we could access the
`this->current` member of std::reverse_iterator from a derived
class, but in doing so we incremented a null iterator, which is UB.
We always want to build the table of contents. Additionally, we also
set the flag to make the output deterministic which is already the
default for llvm-ar.
Differential Revision: https://reviews.llvm.org/D74108
Summary: This review is a mostly trivial change to use an explicit ABI flag for the unstable external template list. This follows the practice for an ABI flag per feature, and provides a spot for the rational / motivation for the flag.
Reviewers: EricWF, ldionne
Subscribers: dexonsmith, libcxx-commits
Tags: #libc
Differential Revision: https://reviews.llvm.org/D75457
I've been sitting on this change for a while and have been using
it to build the bot images, so it should be upstream.
This re-configures the docker build files to use docker-compose
more heavily. This allows for composing large images with multiple
compilers without invalidating the docker caches.
After this commit I'll quickly switch all the current buildbots
over to a new docker image, followed by another update to add new
compilers
These tests check that an operations happens within a specified
deadline, which causes flaky failures on slow machines or machines
under heavy load.
By adding the // FLAKY_TEST. tag it allows the test suite to
retry or ignore the tests
The markup wasn't quite right, and that broke compilation with availability
markup enabled. I'm disabling it until I have time to fix it properly to
get the CI mostly green again.
Summary:
This change checks for the case where people want to erase a string to the end, i.e., __n == npos, and inlines the call if so.
This also demonstrates keeping the ABI intact for V1, but inlining the erase() method for unstable.
Reviewers: EricWF, mclow.lists, ldionne
Reviewed By: EricWF, ldionne
Subscribers: smeenai, dexonsmith, christof, libcxx-commits
Tags: #libc
Differential Revision: https://reviews.llvm.org/D73743
Summary:
The definition of `__libcpp_timed_backoff_policy` and the declaration of
`__libcpp_thread_poll_with_backoff` must not be guarded by
#if !defined(_LIBCPP_HAS_THREAD_API_EXTERNAL)
because the definitions of `__libcpp_timed_backoff_policy::operator()`
and `__libcpp_thread_poll_with_backoff` aren't guarded by this macro
(and this is correct because these two functions are implemented in
terms of other libc++ functions and don't interact with the host
threading library).
Reviewers: ldionne, __simt__, EricWF, mclow.lists
Reviewed By: ldionne
Subscribers: dexonsmith, libcxx-commits
Tags: #libc
Differential Revision: https://reviews.llvm.org/D75191
Summary:
This change adds the macros _LIBCPP_COMPILER_HAS_BUILTIN_CONSTANT and _LIBCPP_BUILTIN_CONSTANT_P to detect compile time constants, and optimze the code accordingly.
A planned usage example:
The implementation of basic_string::assign() can short-cut a compile time known short string assignent into a fast and compact inlined assignment:
```
basic_string::assign(const value_type* __s) {
if (_LIBCPP_BUILTIN_CONSTANT_P(__s[0]) && length(__s) < __min_cap) {
copy(pointer(), _s, length(__s) + 1);
set_size(length(__s));
} else {
// delegate / tail call out of line implementation
}
}
```
Subscribers: christof, libcxx-commits
Tags: #libc
Differential Revision: https://reviews.llvm.org/D73732
std::shared_ptr::allocate_shared isn't in the standard. This commit removes it from libc++. It updates std::allocate_shared to use __create_with_cntrl_block.
Differential Revision: https://reviews.llvm.org/D66178
It turns out that <semaphore.h> is not well-behaved, as it transitively
includes <sys/param.h>, and that one defines several non-reserved macros
that clash with some downstream projects in modular builds. For the time
being, using <sys/semaphore.h> instead gives us the declarations we need
without the macros.
rdar://59744472
Move the implementation of __libcpp_thread_poll_with_backoff
and __libcpp_timed_backoff_policy::operator() out of the
_LIBCPP_HAS_THREAD_API_PTHREAD block. None of the code in these
methods is pthreads specific.
Also add "inline _LIBCPP_INLINE_VISIBILITY" to
__libcpp_timed_backoff_policy::operator(), to avoid errors due to
multiple definitions of the operator. Contrary to
__libcpp_thread_poll_with_backoff (which is a template function),
this is a normal non-templated method.
Differential Revision: https://reviews.llvm.org/D75102
Summary:
In libc++, we normally #ifdef out header content instead of #erroring
out when the Standard in use is insufficient for the requirements of
the header.
Reviewers: EricWF
Subscribers: jkorous, dexonsmith, libcxx-commits, teemperor
Tags: #libc
Differential Revision: https://reviews.llvm.org/D75074
Depend on the compiler to provide a correct implementation of
max_align_t. If __STDCPP_NEW_ALIGNMENT__ is missing and C++03 mode has
been explicitly enabled, provide a minimal fallback in <new> as
alignment of the largest primitive types.
https://reviews.llvm.org/D68480 added those headers and made the std module
only usable with C++14 or later as the submodules were not marked as requiring
C++14 or later. This just adds the missing requires directives.
- Avoid using C++11-and-later features in <atomic>:
Historically, we've supported <atomic> in C++03, so we can't use C++11
features in that header. This is something we really need to change,
since our implementation of <atomic> is starting to accumulate technical
debt because of that.
- Mark a test as unsupported on single threaded systems
- Add missing symbols to the Linux ABI list
Summary: We want to eventually remove it.
Reviewers: EricWF
Subscribers: christof, jkorous, dexonsmith, libcxx-commits
Tags: #libc
Differential Revision: https://reviews.llvm.org/D74719
- Add the new symbols to the ABI list on Darwin
- Add XFAIL markup to the tests that require dylib support on older platforms
- Add availability markup for back-deployment
Otherwise, the `availability=XXX` lit feature is set even when we're
testing trunk and _LIBCPP_DISABLE_AVAILABILITY is defined, which causes
tests that check for availability markup to be enabled and unexpectedly
pass.
This change splits the _LIBCPP_STRING_EXTERN_TEMPLATE_LIST up into a _LIBCPP_STRING_V1_EXTERN_TEMPLATE_LIST containing the stable ABI, and a _LIBCPP_STRING_UNSTABLE_EXTERN_TEMPLATE_LIST containing the unstable ABI.
The purpose is to explicitly define and maintain the two lists, where the unstable ABI allows for ABI breaking changes for purposes such as optimization while offering a strong guarantee that any change inside the unstable ABI does not affect the stable ABI.
As per the comment in the __string header, we do still allow etries to be added to the stable ABI list as the c++ versions and corresponding c++ std API changes.
This patch enables throwing exceptions for invalid backreferences
in the constructor when using the basic, extended, grep, or egrep grammar.
This fixes bug 34297.
Differential Revision: https://reviews.llvm.org/D62453
This patch qualifies calls to ref and cref inside ref(reference_wrapper<T>)
and cref(reference_wrapper<T>), respectively. These previously unqualified
calls could break in the presence of user functions called ref/cref inside
associated namespaces: https://gcc.godbolt.org/z/8VfprT
Fixes PR44398.
Differential Revision: https://reviews.llvm.org/D74287
Instead of including <ios> for ios_base::failbit, simply get failbit
member of the template argument. Print directly to a stream instead
of using intermediate ostringstream.
Parsing time: 874ms -> 164ms (-81%)
Thanks to Nikita Kniazev for the patch!
Differential Revision: https://reviews.llvm.org/D71214
The regex backreferences were not properly parsed and used when using
the extended grammar. This change parses them. The issue was found while
working on PR34297.
Thanks to Mark de Wever for the patch!
Differential Revision: https://reviews.llvm.org/D62451
The libc++ __bit_iterator type has weird ABI calling conventions as a
quirk
of the implementation. The const bit iterator is trivial, but the
non-const
bit iterator is not because it declares a user-defined copy constructor.
Changing this now is an ABI break, so this test ensures that each type
is trivial/non-trivial as expected.
The definition of 'non-trivial for the purposes of calls':
A type is considered non-trivial for the purposes of calls if:
* it has a non-trivial copy constructor, move constructor, or
destructor, or
* all of its copy and move constructors are deleted.
This reverts commit 82b47b2978.
This broke Clang and LLDB module builds without -fmodules-local-submodule-visbility.
I'll revert this for now until we have a fix and reland once Clang
can properly handle this code.
See also the discussion in https://reviews.llvm.org/rG82b47b2978405f802a33b00d046e6f18ef6a47be
libc++ is careful to not fracture overload sets. When one overload
is visible to a user, all of them should be. Anything less causes
subtle bugs and ODR violations.
Previously, in order to support ::abs and ::div being supplied by
both <cmath> and <cstdlib> we had to do awful things that make
<math.h> and <stdlib.h> have header cycles and be non-modular.
This really breaks with modules.
Specifically the problem was that in C++ ::abs introduces overloads
for floating point numbers, these overloads forward to ::fabs,
which are defined in math.h. Therefore ::abs needed to be in math.h
too. But this required stdlib.h to include math.h and math.h to
include stdlib.h.
To avoid these problems the definitions have been moved to stddef.h
(which math includes), and the floating point overloads of ::abs
have been changed to call __builtin_fabs, which both Clang and GCC
support.
There are some unnecessary typenames in std/numerics/c.math/abs.pass.cpp;
e.g. they're not in a dependent context.
Patch by Bryce Adelstein Lelbach
Differential Revision: https://reviews.llvm.org/D72106
The static asserts in span<T, N>::front() and span<T, N>::back() are
incorrect as they may be triggered from valid code due to evaluation
of a never taken branch:
span<int, 0> foo;
if (!foo.empty()) {
auto x = foo.front();
}
The problem is that the branch is always evaluated by the compiler,
creating invalid compile errors for span<T, 0>.
Thanks to Michael Schellenberger Costa for the patch.
Differential Revision: https://reviews.llvm.org/D71995
Summary:
In D27429, we switched the Apple implementation of steady_clock::now()
from clock_gettime(CLOCK_MONOTONIC) to clock_gettime(CLOCK_UPTIME_RAW).
The purpose was to get nanosecond precision, and also to improve the
performance of the implementation.
However, it appears that CLOCK_UPTIME_RAW does not satisfy the requirements
of the Standard, since it is not strictly speaking monotonic. Indeed, the
clock does not increment while the system is asleep, which had been
mentioned in D27429 but somehow not addressed.
This patch switches to CLOCK_MONOTONIC_RAW, which is monotonic, increased
during sleep, and also has nanosecond precision.
https://llvm.org/PR44773
Reviewers: bruno, howard.hinnant, EricWF
Subscribers: christof, jkorous, dexonsmith, libcxx-commits, mclow.lists, EricWF
Tags: #libc
Differential Revision: https://reviews.llvm.org/D74341
The calculation _Offset + _Count <= size() may overflow, so use
_Count <= size() - _Offset instead. Note that this is safe due to
the previous constraint that _Offset <= size().
Patch by Michael Schellenberger Costa.
Differential Revision: https://reviews.llvm.org/D71998
Summary:
In `std::filesystem::proximate` tests we assume that the current working directory's name
is `fs.op.proximate`. This is fine when we're running the tests locally.
However, if we're running those tests on a remote machine via SSH, the directory layout may be
different. For example, currently we copy each test executable individually into
a temporary directory on the target board using SCP, so the assumption about the working directory name
doesn't necessarily hold.
This patch is the only thing that is necessary for all libc++ tests to pass when run remotely.
Reviewers: ldionne, EricWF, mclow.lists
Reviewed By: ldionne, EricWF
Subscribers: christof, dexonsmith, libcxx-commits
Tags: #libc
Differential Revision: https://reviews.llvm.org/D74348
clang 9ce6dc9872 drops support for
implicit conversion of nullptr_t to bool. From that commit:
The C++ rules briefly allowed this, but the rule changed nearly 10
years ago and we never updated our implementation to match. However,
we've warned on this by default for a long time, and no other compiler
accepts (even as an extension).
The system libc++.dylib doesn't support the debug mode, so this test
can't be supported. As a fly-by fix, we also specify more stringently
that only the macOS system library is unsupported in other tests using
the debug mode.
The extent of the returned span was always std::dynamic_extent, which
is incorrect.
Thanks to Michael Schellenberger Costa for the patch.
Differential Revision: https://reviews.llvm.org/D71997
size_t is always greater than 0, so remove the artifact from the old
index_type.
Patch by Michael Schellenberger Costa.
Differential Revision: https://reviews.llvm.org/D71996
Both methods have compile time constraints that we should test against.
Patch by Michael Schellenberger Costa
Differential Revision: https://reviews.llvm.org/D71999
Louis Dionne