We've stopped doing it in libc++ for a while now because these names
would end up rotting as we move things around and copy/paste stuff.
This cleans up all the existing files so as to stop the spreading
as people copy-paste headers around.
Some embedded platforms do not wish to support the C library functionality
for handling wchar_t because they have no use for it. It makes sense for
libc++ to work properly on those platforms, so this commit adds a carve-out
of functionality for wchar_t.
Unfortunately, unlike some other carve-outs (e.g. random device), this
patch touches several parts of the library. However, despite the wide
impact of this patch, I still think it is important to support this
configuration since it makes it much simpler to port libc++ to some
embedded platforms.
Differential Revision: https://reviews.llvm.org/D111265
In basic_string and vector, we've been encapsulating all exception
throwing code paths in helper functions of a base class, which are defined
in the compiled library. For example, __vector_base_common defines two
methods, __throw_length_error() and __throw_out_of_range(), and the class
is externally instantiated in the library. This was done a long time ago,
but after investigating, I believe the goal of the current design was to:
1. Encapsulate the code to throw an exception (which is non-trivial) in
an externally-defined function so that the important code paths that
call it (e.g. vector::at) are free from that code. Basically, the
intent is for the "hot" code path to contain a single conditional jump
(based on checking the error condition) to an externally-defined function,
which handles all the exception-throwing business.
2. Avoid defining this exception-throwing function once per instantiation
of the class template. In other words, we want a single copy of
__throw_length_error even if we have vector<int>, vector<char>, etc.
3. Encapsulate the passing of the container-specific string (i.e. "vector"
and "basic_string") to the underlying exception-throwing function
so that object files don't contain those duplicated string literals.
For example, we'd like to have a single "vector" string literal for
passing to `std::__throw_length_error` in the library, instead of
having one per translation unit.
However, the way this is achieved right now has two problems:
- Using a base class and exporting it is really weird - I've been confused
about this ever since I first saw it. It's just a really unusual way of
achieving the above goals. Also, it's made even worse by the fact that
the definitions of __throw_length_error and __throw_out_of_range appear
in the headers despite always being intended to be defined in the compiled
library (via the extern template instantiation).
- We end up exporting those functions as weak symbols, which isn't great
for load times. Instead, it would be better to export those as strong
symbols from the library.
This patch fixes those issues while retaining ABI compatibility (e.g. we
still export the exact same symbols as before). Note that we need to
keep the base classes as-is to avoid breaking the ABI of someone who
might inherit from std::basic_string or std::vector.
Differential Revision: https://reviews.llvm.org/D111173
In other places in the code, we use lowercase spelling for things that
are not available in prior standards.
Differential Revision: https://reviews.llvm.org/D109435
Detected by evil-izing the widely used `MoveOnly` testing type.
I had to patch some tests that were themselves using its comma operator,
but I think that's a worthwhile cost in order to catch more places
in our headers that needed comma-proofing.
The trick here is that even `++ptr, SomeClass()` can find a comma operator
by ADL, if `ptr` is of type `Evil*`. (A comma between two operands
of non-class-or-enum type is always treated as the built-in
comma, without ADL. But if either operand is class-or-enum, then
ADL happens for _both_ operands' types.)
Differential Revision: https://reviews.llvm.org/D109414
I just ran into a compiler error involving __bind_back and some overloads
that were being disabled with _EnableIf. I noticed that the error message
was quite bad and did not mention the reason for the overload being
excluded. Specifically, the error looked like this:
candidate template ignored: substitution failure [with _Args =
<ContiguousView>]: no member named '_EnableIfImpl' in 'std::_MetaBase<false>'
Instead, when using enable_if or enable_if_t, the compiler is clever and
can produce better diagnostics, like so:
candidate template ignored: requirement 'is_invocable_v<
std::__bind_back_op<1, std::integer_sequence<unsigned long, 0>>,
std::ranges::views::__transform::__fn &, std::tuple<PlusOne> &,
ContiguousView>' was not satisfied [with _Args = <ContiguousView>]
Basically, it tries to do a poor man's implementation of concepts, which
is already a lot better than simply complaining about substitution failure.
Hence, this commit uses enable_if_t instead of _EnableIf whenever
possible. That is both more straightforward than using the internal
helper, and also leads to better error messages in those cases.
I understand the motivation for _EnableIf's implementation was to improve
compile-time performance, however I believe striving to improve error
messages is even more important for our QOI, hence this patch. Furthermore,
it is unclear that _EnableIf actually improved compile-time performance
in any noticeable way (see discussion in the review for details).
Differential Revision: https://reviews.llvm.org/D108216
There is a lot more we can do, in particular in <type_traits>, but this
removes some workarounds that were gated on checking a specific compiler
version.
Differential Revision: https://reviews.llvm.org/D108923
basic_string and vector currently have a hard dependency on the compiled
library because they need to call __vector_base_common::__throw_xxx(),
which are externally instantiated in the compiled library. That makes
sense when exceptions are enabled (because we're trying to localize the
exception-throwing code to the compiled library), but it doesn't really
make sense when exceptions are disabled, and the __throw_xxx functions
are just calling abort() anyways.
This patch simply overrides the __throw_xxx() functions so that they
don't rely on the compiled library when exceptions are disabled.
Differential Revision: https://reviews.llvm.org/D108389
All supported compilers have supported deduction guides in C++17 for a
while, so this isn't necessary anymore.
Differential Revision: https://reviews.llvm.org/D108213
With the STL containers, I didn't enable move operations in C++03 mode
because that would change the overload resolution for things that today
are copy operations. With iostreams, though, the copy operations aren't
present at all, and so I see no problem with enabling move operations
even in (Clang's greatly extended) C++03 mode.
Clang's C++03 mode does not support delegating constructors.
Differential Revision: https://reviews.llvm.org/D104310
This appears to be a bug in our string::assign: when assigning into
a longer string, from a shorter snippet of itself, we invalidate
iterators before doing the copy. We should invalidate them afterward.
Also drive-by improve the formatting of a function header.
Differential Revision: https://reviews.llvm.org/D101675
This reverts a large chunk of http://reviews.llvm.org/D15862 ,
and also fixes bugs in `insert`, `append`, and `assign`, which are now regression-tested.
(Thanks to Tim Song for pointing out the bug in `append`!)
Before this patch, we did a special dance in `append`, `assign`, and `insert`
(but not `replace`). All of these require the strong exception guarantee,
even when the user-provided InputIterator might have throwing operations.
The naive way to accomplish this is to construct a temporary string and
then append/assign/insert from the temporary; i.e., finish all the potentially
throwing and self-inspecting InputIterator operations *before* starting to
modify self. But this is slow, so we'd like to skip it when possible.
The old code (D15682) attempted to check that specific iterator operations
were nothrow: it assumed that if the iterator operations didn't throw, then
it was safe to iterate the input range multiple times and therefore it was
safe to use the fast-path non-naive version. This was wrong for two reasons:
(1) the old code checked the wrong operations (e.g. checked noexceptness of `==`,
but the code that ran used `!=`), and (2) the conversion of value_type to char
could still throw, or inspect the contents of self.
The new code is much simpler, although still much more complicated than it
really could be. We'll likely revisit this codepath at some point, but for now
this patch suffices to get it passing all the new regression tests.
The added tests all fail before this patch, and succeed afterward.
See https://quuxplusone.github.io/blog/2021/04/17/pathological-string-appends/
Differential Revision: https://reviews.llvm.org/D98573
As mandated by the Standard's various synopses, e.g. [iterator.synopsis].
Searching the TeX source for '#include' is a good way to find all of these
mandates.
The new tests are all autogenerated by utils/generate_header_inclusion_tests.py.
I was SHOCKED by how many mandates there are, and how many of them
libc++ wasn't conforming with.
Differential Revision: https://reviews.llvm.org/D99309
Specifically, use these metafunctions consistently in areas that are
about to be affected by P1518R2's changes.
This is the NFCI part of https://reviews.llvm.org/D97742 .
The functional-change part is still waiting for P1518R2 to be
officially merged into the working draft.
Left to finish P0482:
* <cuchar> header.
* Parts of <memory_resource> concerning char8_t. Also, tests for hash<pmr::*string>.
Reviewed By: ldionne, #libc, Quuxplusone
Differential Revision: https://reviews.llvm.org/D99184
This fixes clang warnings (that are treated as errors when running
the test suite):
libcxx/include/string:4409:59: error: definition of dllimport static field [-Werror,-Wdllimport-static-field-def]
basic_string<_CharT, _Traits, _Allocator>::npos;
The warning is normally not visible as long as the libc++ headers
are treated as system headers.
The same construct is always an error in MSVC.
(One _LIBCPP_FUNC_VIS was added in
2d8f23f571, which broke DLL builds.
59919c4d6b fixed this by adding another
_LIBCPP_FUNC_VIS on the declaration for consistency, but the underlying
issue remained, that one can't use dllimport here.)
Differential Revision: https://reviews.llvm.org/D97168
Adds `noexcept` to `string_view`/`string::find` and similar members
(`rfind`, etc.). See discussion in D95251. Refs D95821.
Reviewed By: curdeius, ldionne
Differential Revision: https://reviews.llvm.org/D95848
* The only exception is that the flag -std=c++2a is still used not to break compatibility with older compilers (clang <= 9, gcc <= 9).
* Bump _LIBCPP_STD_VER for C++20 to 20 and use 21 for the future standard (C++2b).
That's a preparation step to add c++2b support to libc++.
Reviewed By: ldionne, #libc
Differential Revision: https://reviews.llvm.org/D93383
Generally these calls aren't vulnerable to ADL because they involve only
primitive types. The ones in <list> and <vector> drag in namespace std
but that's OK; the ones in <fstream> and <strstream> are vulnerable
iff `CharT` is an enum type, which seems far-fetched.
But absolutely zero of them *need* ADL to happen; so in my opinion
they should all be consistently qualified, just like calls to any
other (non-user-customizable) functions in namespace std.
Also: Include <cstring> and <cwchar> in <__string>.
We seemed to be getting lucky that <memory> included <iterator>
included <iosfwd> included <wchar.h>. That gave us the
global-namespace `wmemmove`, but not `_VSTD::wmemmove`.
This is now fixed.
I didn't touch these headers:
<ext/__hash> uses strlen, safely
<support/ibm/locale_mgmt_aix.h> uses memcpy, safely
<string.h> uses memchr and strchr, safely
<wchar.h> uses wcschr, safely
<__bsd_locale_fallbacks.h> uses wcsnrtombs, safely
Differential Revision: https://reviews.llvm.org/D93061
This attribute permits a typedef to be associated with a class template
specialization as a preferred way of naming that class template
specialization. This permits us to specify that (for example) the
preferred way to express 'std::basic_string<char>' is as 'std::string'.
The attribute is applied to the various class templates in libc++ that have
corresponding well-known typedef names.
This is a re-commit. The previous commit was reverted because it exposed
a pre-existing bug that has since been fixed / worked around; see
PR48434.
Differential Revision: https://reviews.llvm.org/D91311
This change exposed a pre-existing issue with deserialization cycles
caused by a combination of attributes and template instantiations
violating the deserialization ordering restrictions; see PR48434 for
details.
A previous commit attempted to work around PR48434, but appears to have
only been a partial fix, and fixing this properly seems non-trivial.
Backing out for now to unblock things.
This reverts commit 98f76adf4e and
commit a64c26a47a.
This attribute permits a typedef to be associated with a class template
specialization as a preferred way of naming that class template
specialization. This permits us to specify that (for example) the
preferred way to express 'std::basic_string<char>' is as 'std::string'.
The attribute is applied to the various class templates in libc++ that have
corresponding well-known typedef names.
Differential Revision: https://reviews.llvm.org/D91311
This reverts commit 620adacf87.
Fix: unsupport C++03 for the new test, define helpers before __swap_allocator
(1) Add _VSTD:: qualification to __swap_allocator.
(2) Add _VSTD:: qualification consistently to __to_address.
(3) Add some more missing _VSTD:: to <vector>, with a regression test.
This part is cleanup after d9a4f936d0.
Note that a vector whose allocator actually runs afoul of any of these ADL calls will
likely also run afoul of simple things like `v1 == v2` (which is also an ADL call).
But, still, libc++ should be consistent in qualifying function calls wherever possible.
Relevant blog post: https://quuxplusone.github.io/blog/2019/09/26/uglification-doesnt-stop-adl/
Differential Revision: https://reviews.llvm.org/D91708
(1) Add _VSTD:: qualification to __swap_allocator.
(2) Add _VSTD:: qualification consistently to __to_address.
(3) Add some more missing _VSTD:: to <vector>, with a regression test.
This part is cleanup after d9a4f936d0.
Note that a vector whose allocator actually runs afoul of any of these ADL calls will
likely also run afoul of simple things like `v1 == v2` (which is also an ADL call).
But, still, libc++ should be consistent in qualifying function calls wherever possible.
Relevant blog post: https://quuxplusone.github.io/blog/2019/09/26/uglification-doesnt-stop-adl/
Differential Revision: https://reviews.llvm.org/D91708
__clear_and_shrink() was added in D41976, and a test was added alongside
it to make sure that the string invariants were maintained. However, it
appears that the test never ran under UBSan before, which would have
highlighted the fact that it doesn't actually maintain the string
invariants.
Differential Revision: https://reviews.llvm.org/D88849
The debug mode always had three possibilities:
- _LIBCPP_DEBUG is undefined => no assertions
- _LIBCPP_DEBUG == 0 => some assertions
- _LIBCPP_DEBUG == 1 => some assertions + iterator checks
This was documented that way, however the code did not make this clear
at all. The discrepancy between _LIBCPP_DEBUG and _LIBCPP_DEBUG_LEVEL
was especially confusing. I reworked how the various macros are defined
without changing anything else to make the code clearer.
Summary: We discovered that the compiler may chose not to inline the operator=, which leads to an expensive extra stack frame. This change makes __assign_no_alias always tail called.
Reviewers: EricWF, #libc!
Subscribers: libcxx-commits
Tags: #libc
Differential Revision: https://reviews.llvm.org/D77913
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.
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
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
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.
Summary: This change reflows a comment line. This change serves as a no-op test commit
Reviewers: mclow.lists, ldionne, EricWF
Subscribers: dexonsmith, christof, libcxx-commits
Tags: #libc
Differential Revision: https://reviews.llvm.org/D73552
This reverts commit a8a9c8e0a1.
There are multiple reported failures caused by this change.
Each failure is really weird, but it makes sense to revert
while investigating.
The GCC build failures have been addressed, and the LLDB failures were
fixed by LLDB.
I have also verified that the apple-clang 9.0 segfault no longer
occurs.
Original Message:
The external instantiation of std::string is a problem for libc++.
Additions and removals of inline functions in string can cause ABI
breakages, including introducing new symbols.
This patch aims to:
(1) Make clear which functions are explicitly instatiated.
(2) Prevent new functions from being accidentally instantiated.
(3) Allow a migration path for adding or removing functions from the
explicit instantiation over time.
Although this new formulation is uglier, it is preferable from a
maintainability and readability standpoint because it explicitly
enumerates the functions we've chosen to expose in our ABI. Changing
this list is non-trivial and requires thought and planning.
(3) is achieved by making it possible to control the extern template declaration
separately from it's definition. Meaning we could add a new definition to
the dylib, wait for it to roll out, then add the extern template
declaration to the header. Similarly, we could remove existing extern
template declarations while still keeping the definition to prevent ABI
breakages.
This patch is needed in order to work around a GCC bug that fails to
explicitly instantiate a non-template function of a class template when
there is another overload that's a function template.
(See https://godbolt.org/z/4bUQ_b)
This patch SFINAE's away the function templates when the argument is
a basic_string.
The external instantiation of std::string is a problem for libc++.
Additions and removals of inline functions in string can cause ABI
breakages, including introducing new symbols.
This patch aims to:
(1) Make clear which functions are explicitly instatiated.
(2) Prevent new functions from being accidentally instantiated.
(3) Allow a migration path for adding or removing functions from the
explicit instantiation over time.
Although this new formulation is uglier, it is preferable from a
maintainability and readability standpoint because it explicitly
enumerates the functions we've chosen to expose in our ABI. Changing
this list is non-trivial and requires thought and planning.
(3) is achieved by making it possible to control the extern template declaration
separately from it's definition. Meaning we could add a new definition to
the dylib, wait for it to roll out, then add the extern template
declaration to the header. Similarly, we could remove existing extern
template declarations while still keeping the definition to prevent ABI
breakages.
This patch de-duplicates most compressed pair constructors
to use the same code in C++11 and C++03.
Part of doing that is deleting the "__second_tag()" and replacing
it with a "__value_init_tag()" which has the same effect, but
allows for the removal of the special "one-arg" first element
constructor.
This patch is intended to have no semantic change.
With the upcoming introduction of iterator concepts in ranges,
the meaning of "__is_contiguous_iterator" changes drastically.
Currently we intend it to mean "does it have this iterator category",
but it could now also mean "does it meet the requirements of this
concept", and these can be different.
This function has the same behavior as the now-standand std::to_address.
Re-using the name makes the behavior more clear, and in the future it
will allow us to correctly get the raw pointer for user provided pointer
types.
Summary:
This is effectively a revert of r344616, which was a partial fix for
PR38964 (compilation of <string> with GCC in C++03 mode). However, that
configuration is explicitly not supported anymore and that partial fix
breaks compilation with Clang when per-TU insulation is provided.
PR42676
rdar://52899715
Reviewers: mclow.lists, EricWF
Subscribers: christof, jkorous, dexonsmith, libcxx-commits
Tags: #libc
Differential Revision: https://reviews.llvm.org/D64941
llvm-svn: 366567
Summary:
The reason libc++ implemented a throwing debug mode handler was for ease of testing. Specifically,
I thought that if a debug violation aborted, we could only test one violation per file. This made
it impossible to test debug mode. Which throwing behavior we could test more!
However, the throwing approach didn't work either, since there are debug violations underneath noexcept
functions. This lead to the introduction of `_NOEXCEPT_DEBUG`, which was only noexcept when debug
mode was off.
Having thought more and having grown wiser, `_NOEXCEPT_DEBUG` was a horrible decision. It was
viral, it didn't cover all the cases it needed to, and it was observable to the user -- at worst
changing the behavior of their program.
This patch removes the throwing debug handler, and rewrites the debug tests using 'fork-ing' style
death tests.
Reviewers: mclow.lists, ldionne, thomasanderson
Reviewed By: ldionne
Subscribers: christof, arphaman, libcxx-commits, #libc
Differential Revision: https://reviews.llvm.org/D59166
llvm-svn: 356417
to reflect the new license.
We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.
Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.
llvm-svn: 351636
This attribute should appear only on the first declaration. This
patch cleans up <string> by removing the attribute on redeclarations.
llvm-svn: 347608
This patch adds an implementation of __resize_default_init as
described in P1072R2. Additionally, it uses it in filesystem to
demonstrate its intended utility.
Once P1072 lands, or if it changes it's interface, I will adjust
the internal libc++ implementation to match.
llvm-svn: 347589
r347395 changed the ABI list on Linux, but two of those symbols are still
being exported from the shared object:
_ZSt18make_exception_ptrINSt3__112future_errorEESt13exception_ptrT_
_ZNSt3__1plIcNS_11char_traitsIcEENS_9allocatorIcEEEENS_12basic_stringIT_T0_T1_EERKS9_PKS6_
This commit makes sure those symbols are not exported, as they should be.
llvm-svn: 347399
Summary:
This commit marks a few functions as hidden and removes them from the ABI list
on Linux such that libc++ can be built with -fvisibility=hidden. The functions
marked as hidden by this patch were exported from the shared object only
because they were implicitly instantiated function templates. It is safe
to stop exporting those symbols from the shared object because nobody could
actually depend on them: implicit instantiations are not taken from shared
objects.
The symbols removed in this commit are basically the same that had been
removed in https://reviews.llvm.org/D53868, but that patch had to be reverted
because it broke the build (because the functions were not marked as hidden
like this patch does).
Reviewers: EricWF, mclow.lists
Subscribers: christof, jkorous, dexonsmith, libcxx-commits
Differential Revision: https://reviews.llvm.org/D54639
llvm-svn: 347395
When an always_inline function is used prior to the functions definition,
the compiler may not be able to inline it as requested by the attribute.
GCC flags the `basic_string(CharT const*)` function as one such example.
This patch supresses the warning, and the problem, by moving the
definition of the string constructor to the inline declaration.
This ensures the body is available when it is first ODR used.
llvm-svn: 337235
shrink_to_fit() ends up doing a lot work to get information that we
already know since we just called clear(). This change seems concise
enough to be worth the couple extra lines and my benchmarks show that it
is indeed a pretty decent win. It looks like the same thing is going on
twice in __copy_assign_alloc(), but I didn't want to go overboard since
this is my first contribution to llvm/libc++.
Patch by Timothy VanSlyke!
Differential Revision: https://reviews.llvm.org/D41976
llvm-svn: 327064
The non-const data() member of std::string is only exposed
in C++17 and beyond. However std::string is externally instantiated
and so the member function needs to be exposed to be externally instantiated.
On Linux and OS X this shouldn't cause a problem, because
_LIBCPP_INLINE_VISIBILITY ensures the symbol is always inlined.
However on Windows, the symbol gets marked dllimport, but
there is no definition to import, causing link errors.
llvm-svn: 318690
Previously this macro used 0/1 to indicate if it was set.
This is unlike all other libc++ configuration macros which
use ifdef/ifndef.
This patch makes this macro consistent with everything else.
llvm-svn: 315995
This function template is referenced inside class basic_string as a
friend function. The extern template declaration needs to be above that
friend declaration to actually take effect.
This is important because this function was marked as exported in
r307966, so without the extern template taking effect, it can leak into
other DSOs as a visible symbol.
llvm-svn: 309474
Nikolas Klauser