Summary:
bad_function_call is currently an empty class, so any object files using
that class will end up with their own copy of its typeinfo, typeinfo
name and vtable, leading to unnecessary duplication that has to be
resolved by the dynamic linker. Instead, give bad_function_call a key
function and put a definition for that key function in libc++ itself, to
centralize the typeinfo and vtable.
This is consistent with the behavior for other exception classes. The
key functions are defined in libc++ rather than libc++abi since the
class is defined in the libc++ versioning namespace, so ABI
compatibility with libstdc++ is not a concern.
Guard this change behind an ABI macro, since it isn't backwards
compatible (i.e., clients built against the new libc++ headers wouldn't
be able to run against an older libc++ library).
Reviewers: mclow.lists, EricWF
Subscribers: mgorny, cfe-commits
Differential Revision: https://reviews.llvm.org/D27387
llvm-svn: 298937
Summary:
Currently both libc++ and libc++abi provide definitions for operator new/delete. However I believe this is incorrect and that one or the other should offer them.
This patch adds the CMake option `-DLIBCXX_ENABLE_NEW_DELETE_DEFINITIONS` which defaults no `ON` unless `-DLIBCXXABI_ENABLE_NEW_DELETE_DEFINITIONS=ON` is specified.
Reviewers: mclow.lists, mehdi_amini, dexonsmith, danalbert, smeenai, mgorny, rmaprath
Reviewed By: mehdi_amini
Subscribers: cfe-commits
Differential Revision: https://reviews.llvm.org/D30516
llvm-svn: 296802
This recommits r294707 with additional fixes. The main difference is
libc++ now correctly builds without any ABI library.
exception.cpp is a bloody mess. It's full of confusing #ifdef branches for
each different ABI library we support, and it's getting unmaintainable.
This patch breaks down exception.cpp into multiple different header files,
roughly one per implementation. Additionally it moves the definitions of
exceptions in new.cpp into the correct implementation header.
This patch also removes an unmaintained libc++abi configuration.
This configuration may still be used by Apple internally but there
are no other possible users. If it turns out that Apple still uses
this configuration internally I will re-add it in a later commit.
See http://llvm.org/PR31904.
llvm-svn: 294730
exception.cpp is a bloody mess. It's full of confusing #ifdef branches for
each different ABI library we support, and it's getting unmaintainable.
This patch breaks down exception.cpp into multiple different header files,
roughly one per implementation. Additionally it moves the definitions of
exceptions in new.cpp into the correct implementation header.
This patch also removes an unmaintained libc++abi configuration.
This configuration may still be used by Apple internally but there
are no other possible users. If it turns out that Apple still uses
this configuration internally I will re-add it in a later commit.
See http://llvm.org/PR31904.
llvm-svn: 294707
Different platforms implement the wait/sleep functions in difrerent ways.
It makes sense to externalize this into the threading API.
Differential revision: https://reviews.llvm.org/D29630
Reviewers: EricWF, joerg
llvm-svn: 294573
Recently I turned on libc++'s debug mode assertions when
CMake is configured with -DLIBCXX_ENABLE_ASSERTIONS=ON. This
change exposed assertion failures caused by bugs in filesystem.
This patch fixes those failures.
The first bug was that `PathParser` was using front()/back()
on empty string views in order to get the address of the character.
However this is UB on empty strings. Those operations now use data()
to obtain the pointer.
The second bug was that directory_iterator attempted to capture errno when it
was unset and there was an assertion to detect this.
llvm-svn: 294360
This really should get identified properly by the compiler to convert to
a NVRO, but compress the code anyways. This makes the implementation
identical to directory_iterator.cpp
llvm-svn: 294270
N4100 states that an error shall be reported if
`!exists(p) || !is_directory(p)`. We were missing the first half of the
conditional. Invert the error and normal code paths to make the code
easier to follow.
llvm-svn: 294127
It is my opinion that libc++ should never use `<cassert>`, including in the `dylib`.
This patch remove all uses of `assert` from within libc++ and replaces most of them with `_LIBCPP_ASSERT` instead.
Additionally this patch turn `LIBCXX_ENABLE_ASSERTIONS` off by default,
because the standard library should not be aborting user programs unless explicitly asked to.
llvm-svn: 294107
This adds a basic first cut implementation for directory_iterator on
Windows. It uses the FindFirstFile/FindNextFile which has the same
restrictions as opendir/readdir where there exists a TOCTOU race
condition.
llvm-svn: 293531
Microsoft's SAL has a `__deref` macro which results in a compilation
failure when building the filesystem module on Windows. Rename the
member function internally to avoid the conflict.
llvm-svn: 293449
This reverts commit r292883. Unfortunately <string_view> uses
_LIBCPP_ASSERT in a way which is not compatible with the C++11 dylib
build. I'll investigate more tomorrow.
llvm-svn: 292923
Summary:
It is my opinion that libc++ should never use `<cassert>`, including in the `dylib`. This patch remove all uses of `assert` from within libc++ and replaces most of them with `_LIBCPP_ASSERT` instead.
Additionally this patch turn `LIBCXX_ENABLE_ASSERTIONS` off by default, because the standard library should not be aborting user programs unless explicitly asked to.
Reviewers: mclow.lists, compnerd, smeenai
Reviewed By: mclow.lists
Subscribers: mgorny, cfe-commits
Differential Revision: https://reviews.llvm.org/D29063
llvm-svn: 292883
Summary:
This patch disables the aligned new/delet overloads on Apple platforms without `posix_memalign`. This fixes libc++.dylib build regressions on such platforms.
This fixes http://llvm.org/PR31448.
This patch should also be merged into the 4.0 release branch
Reviewers: mclow.lists, rsmith, dexonsmith, jeremyhu
Reviewed By: mclow.lists
Subscribers: cfe-commits
Differential Revision: https://reviews.llvm.org/D28931
llvm-svn: 292564
In order to allow inlining of previously out-of-line functions without an ABI break
libc++ provides legacy definitions in the dylib that old programs can
continue to use. Unfortunatly Windows link.exe detects this hack and diagnoses the duplicate
definitions.
This patch disable the duplicate definitions on Windows by adding an ABI option
which disables all "legacy out-of-line symbols"
llvm-svn: 292190
Moves hot functions such as atomic add into the memory header file
so that they can be inlined, which brings performance benefits.
Patch by Kevin Hu, Aditya Kumar, Sebastian Pop
Differential Revision: https://reviews.llvm.org/D24991
llvm-svn: 292184
This patch contains multiple cleanups and fixes to better support building on
Windows.
* [Test] Fix handling of library runtime search paths by correctly adding them
to the PATH variable when running the tests.
* [Test] Don't explicitly force "--target=i686-pc-windows" when running the
test suite. Clang++ seems to deduce the correct target.
* [Test] Fix `.sh.cpp` tests on Windows by properly escaping flags used in
shell commands. Specifically windows style paths which included spaces
were causing these tests to fail.
* [CMake] Add "vcruntime" to the list of supported C++ ABI libraries in CMake, and
teach the test suite how to handle it. For now libc++ defaults to using
"vcruntime" on Windows except when libc++abi is in tree; That is probably
a bug and should be changed to always use vcruntime, at least for now.
* [Misc] Move the "c++-build" include directory to the libc++ binary dir
instead of the top level project dir and rename it "c++build". This is just
misc cleanup. Libc++ shouldn't be creating internal build files and directories
at the top-level projects root.
* [Misc] Build type_info's destructor when building for MSVC. This is a temporary
work around to prevent link errors until we have a proper type_info
implementation.
llvm-svn: 292157
Attempting to pair an `_aligned_malloc` with a regular free causes heap
corruption. Pairing with `_aligned_free` is required instead.
Makes the following libc++ tests pass on Windows:
```
std/language.support/support.dynamic/new.delete/new.delete.array/new_align_val_t.pass.cpp
std/language.support/support.dynamic/new.delete/new.delete.array/new_align_val_t_nothrow.pass.cpp
std/language.support/support.dynamic/new.delete/new.delete.single/new_align_val_t.pass.cpp
std/language.support/support.dynamic/new.delete/new.delete.single/new_align_val_t_nothrow.pass.cpp
```
Differential Revision: https://reviews.llvm.org/D28512
llvm-svn: 291743
Use CLOCK_UPTIME_RAW in case clock_gettime is available on Darwin.
On Apple platforms only CLOCK_UPTIME_RAW or mach_absolute_time are able
to time functions in the nanosecond range. Thus, they are the only
acceptable implementations of steady_clock.
Differential Revision: https://reviews.llvm.org/D27429
rdar://problem/29449467
llvm-svn: 291466
ELAST should point to the last valid error string value. However,
`_sys_nerr` provides the number of elements in the errlist array. Since
the index is 0-based, this is off-by-one. Adjust it accordingly.
Thanks to David Majnemer for catching this!
llvm-svn: 291336
Summary:
On Windows the identifier `__deallocate` is defined as a macro by one of the Windows system headers. Previously libc++ worked around this by `#undef __deallocate` and generating a warning. However this causes the WIN32 version of `__threading_support` to always generate a warning on Windows. This is not OK.
This patch renames all usages of `__deallocate` internally as to not conflict with the macro.
Reviewers: mclow.lists, majnemer, rnk, rsmith, smeenai, compnerd
Subscribers: cfe-commits
Differential Revision: https://reviews.llvm.org/D28426
llvm-svn: 291332
Windows does not provide an implementation of `nanosleep`. Round up the
time duration to the nearest ms and use `Sleep`. Although this may
over-sleep, there is no hard real-time guarantee on the wake, so
sleeping a bit more is better than under-sleeping as it within the
specification.
llvm-svn: 291331
This patch refactors the compiler detection done in `__config` by creating a
set of `_LIBCPP_COMPILER_<TYPE>` macros. The goal of this patch is to make
it easier to detect what compiler is being used outside of `__config`.
Additionally this patch removes workarounds for GCC in `__bit_reference`. I
tested GCC 4.8 and 4.9 without the workaround and neither seemed to need it
anymore.
llvm-svn: 291286
Split out the recursive and non-recursive mutex. This split is needed
for platforms which may use differing types for the two mutex (e.g.
Win32 threads).
llvm-svn: 291145
In the C++ standard `std::pointer_safety` is defined
as a C++11 strongly typed enum. However libc++ currently defines
it as a class type which simulates a C++11 enumeration. This
can be detected in valid C++ code.
This patch introduces an the _LIBCPP_ABI_POINTER_SAFETY_ENUM_TYPE ABI option.
When defined `std::pointer_safety` is implemented as an enum type.
Unfortunatly this also means it can no longer be provided as an extension
in C++03.
Additionally this patch moves the definition for `get_pointer_safety()`
out of the dylib, and into the headers. New usages of `get_pointer_safety()`
will now use the inline version instead of the dylib version. However in
order to keep the dylib ABI compatible the old definition is explicitly
compiled into it.
llvm-svn: 291046
The name _LIBCPP_TYPE_VIS_ONLY is no longer accurate because both
_LIBCPP_TYPE_VIS and _LIBCPP_TYPE_VIS_ONLY expand to
__attribute__((__type_visibility__)) with Clang. The only remaining difference
is that _LIBCPP_TYPE_VIS_ONLY can be applied to templates whereas
_LIBCPP_TYPE_VIS cannot (due to dllimport/dllexport not being allowed on
templates).
This patch renames _LIBCPP_TYPE_VIS_ONLY to _LIBCPP_TEMPLATE_VIS.
llvm-svn: 291035
A typo and missing header inclusion was obscured by the litany of user
defined literal warnings. This fixes the detection of ELAST on windows.
llvm-svn: 290941
Replace the use of _WIN32 in libc++. Replace most use with a C runtime
check _LIBCPP_MSVCRT or the new _LIBCPP_WIN32 to indicate that we are
using the Win32 API. Use a new _LIBCPP_WCHAR_IS_UCS2 to indicate that we
are on an environment that has a short wchar_t.
llvm-svn: 290910
This patch re-commits a previous attempt to support building libc++ w/o
an ABI library. That patch was originally reverted because:
1) It forgot to teach the test suite about "default" ABI libraries.
2) Some LLVM builders don't clear the CMake cache between builds. The previous
patch caused those builders to fail since their old cache entry for
LIBCXX_CXX_ABI="" is no longer valid.
The updated patch addresses both issues. It works around (2) by adding
a hack to force the builders to update their cache entries. The hack will
be removed shortly once all LLVM builders have run.
Original commit message
-----------------------
Typically libc++ uses libc++abi or libcxxrt to provide the ABI and runtime bits
of the C++ STL. However we also support building w/o an ABI library entirely.
This patch fixes building libc++ w/o an ABI library (and incorporates the
`~type_info()` fix in D28211).
The main changes in this patch are:
1) Add `-DLIBCXX_CXX_ABI=default` instead of using the empty string to mean "default".
2) Fix CMake bits which treated "none" as "default" on OS X.
3) Teach the source files to respect `-D_LIBCPP_BUILDING_HAS_NO_ABI_LIBRARY`.
4) Define ~type_info() when _LIBCPP_BUILDING_HAS_NO_ABI_LIBRARY is defined.
Unfortunately this patch doesn't help clean up the macro mess that we use to
configure for different ABI libraries.
llvm-svn: 290849
Currently libc++ compiles a special version of error_category()
into the dylib. This definition is no longer needed, and doesn't
work on Windows due to dllimport/dllexport semantics.
For those reasons this patch introduces an option to
disable/enable this definition. By default the definition
is provided in ABI v1 except on windows. This patch
also addresses D28210.
llvm-svn: 290840
Typically libc++ uses libc++abi or libcxxrt to provide the ABI and runtime bits
of the C++ STL. However we also support building w/o an ABI library entirely.
This patch fixes building libc++ w/o an ABI library (and incorporates the
`~type_info()` fix in D28211).
The main changes in this patch are:
1) Add `-DLIBCXX_CXX_ABI=default` instead of using the empty string to mean "default".
2) Fix CMake bits which treated "none" as "default" on OS X.
3) Teach the source files to respect `-D_LIBCPP_BUILDING_HAS_NO_ABI_LIBRARY`.
4) Define ~type_info() when _LIBCPP_BUILDING_HAS_NO_ABI_LIBRARY is defined.
Unfortunately this patch doesn't help clean up the macro mess that we use to
configure for different ABI libraries.
llvm-svn: 290839
The locale structures have been made opaque in CRT 14+. This currently
prevents building libc++ for Windows. We can re-enable this in the
future when we have replicated the structure to access the private field
for the name (unless there exists a better supported mechanism to query
the name of a locale given the locale_t).
llvm-svn: 290835
As pointed out by Howard, this is actually 134774 days (* 24 * 3600),
and therefore seconds, not 100ns units. Adjust the units to reflect
reality.
llvm-svn: 290824
Visual C++ 14 and newer split msvcrt into msvcrt and ucrt with flavours
of the ucrt for different environments. This changed the access to the
ctype table by introducing the `__pctype_func` and `__pwctype_func`
accessors. Use this rather than directly accessing `_ctype` which
allows us to be safer in threaded situations by going through the libc
locking.
llvm-svn: 290823
Drawing some inspiration from code from Bill O'Neal as pointed out by
Howard, rework the code to avoid an overflow in the duration. Adjust
the style to match libc++ style as well.
Create a local typedef for the FILETIME duration (100-ns units). Use
this to define the difference between the NT and the UNIX epochs (which
previously overflowed due to the representation limits due to the
bouncing to ns). Return the FILETIME duration biased by the NT-to-UNIX
epoch conversion.
Use of the custom duration makes it easier to read and reason about the
code.
llvm-svn: 290806
system_clock::now is not entirely straight forward on Windows, which
does not have a clock_gettime function.
GetSystemTimeAsFileTime gives us the value relative to the NT epoch (Jan
1 1601) rather than the Unix epoch (Jan 1 1970). However, this function
has a low resolution (~10ms). Newer versions of Windows provide
GetSystemTimePreciseAsFileTime which gives us a much more accurate time
(<1us). Unfortunately, the latter is only available on Windows 8+ when
targeting desktop apps.
llvm-svn: 290803
When building libc++ without threading, strerror_r is not used. Define
the code only when threading is enabled. This allows us to build
system_error for Windows, which ATM doesn't build with threading.
llvm-svn: 290791
This patch implements changes to allow _LIBCPP_ASSERT to throw on failure
instead of aborting. The main changes needed to do this are:
1. Change _LIBCPP_ASSERT to call a handler via a replacable function pointer
instead of calling abort directly. Additionally this patch implements two
handler functions, one which aborts and another that throws an exception.
2. Add _NOEXCEPT_DEBUG macro for disabling noexcept spec on function which
contain _LIBCPP_ASSERT. This is required in order to prevent assertion
failures throwing through a noexcept function. This macro has no effect
unless _LIBCPP_DEBUG_USE_EXCEPTIONS is defined.
Having a non-aborting _LIBCPP_ASSERT is very important to allow sane testing of
debug mode. Currently we can only have one test case per file, since the test
case will cause the program to abort. Testing debug mode this way would require
thousands of test files, most of which would be 95% boiler plate. I don't think
this is a feasible strategy. Fortunately using a throwing debug handler solves
these issues.
Additionally this patch rewrites the documentation for debug mode.
llvm-svn: 290651
Summary:
The underlying C locales provide the `thousands_sep` and `decimal_point` as strings, possible with more than one character. We currently don't handle this case even for `wchar_t`.
This patch properly converts the mbs -> wide character for `moneypunct_byname<wchar_t>`. For the `moneypunct_byname<char>` case we attempt to narrow the WC and if that fails we also attempt to translate it to some reasonable value. For example we translate U00A0 (non-breaking space) into U0020 (regular space). If none of these conversions succeed then we simply allow the base class to provide a fallback value.
Reviewers: mclow.lists, EricWF
Subscribers: vangyzen, george.burgess.iv, cfe-commits
Differential Revision: https://reviews.llvm.org/D24218
llvm-svn: 289347
The function definitions being guarded by the pragma were all static, so
they wouldn't be exported anyway. In any case, we should prefer the
visibility macros. No functional change.
Differential Revision: https://reviews.llvm.org/D26940
llvm-svn: 287768
The code cannot currently link when using libsupc++ with the
LIBCXX_ENABLE_STATIC_ABI_LIBRARY option.
This change ifdef's out the the destructor and 'what' function for
bad_array_length and bad_array_new_length when GLIBCXX is defined.
The constructors that are left in are the only functions not being provided by
libsupc++ itself, and follows the same pattern that was used to ifdef bad_alloc.
Testing was done on a Linux x86_64 host using GCC 5.4 and libc++ from ToT.
I see no change to the test results when using libsup++ or libstdc++ without
LIBCXX_ENABLE_STATIC_ABI_LIBRARY. When using libsupc++ with
LIBCXX_ENABLE_STATIC_ABI_LIBRARY it will now build and test results are the
same as those without the option specified.
Reviewed as https://reviews.llvm.org/D26186
llvm-svn: 287388
This is a generalization of `_LIBCPP_NEW_DELETE_VIS`; the new macro name
captures the semantics better, and also allows us to get rid of the
`_WIN32` check in `include/new`. No functional change.
Differential Revision: https://reviews.llvm.org/D26702
llvm-svn: 287164
This patch fixes a performance bug when constructing or appending to a path
from a string or c-string. Previously we called 'push_back' to append every
single character. This caused multiple re-allocation and copies when at most
one reallocation is necessary. The new behavior is to simply call
`string::append` so it can correctly handle reallocation.
For large strings this change is a ~4x improvement. This also makes our path
faster to construct than libstdc++'s.
llvm-svn: 285530
This patch entirely rewrites the parsing logic for paths. Unlike the previous
implementation this one stores information about the current state; For example
if we are in a trailing separator or a root separator. This avoids the need for
extra lookahead (and extra work) when incrementing or decrementing an iterator.
Roughly this gives us a 15% speedup over the previous implementation.
Unfortunately this implementation is still a lot slower than libstdc++'s.
Because libstdc++ pre-parses and splits the path upon construction their
iterators are trivial to increment/decrement. This makes libc++ lazy parsing
100x slower than libstdc++. However the pre-parsing libstdc++ causes a ton
of extra and unneeded allocations when constructing the string. For example
`path("/foo/bar/")` would require at least 5 allocations with libstdc++
whereas libc++ uses only one. The non-allocating behavior is much preferable
when you consider filesystem usages like 'exists("/foo/bar/")'.
Even then libc++'s path seems to be twice as slow to simply construct compared
to libstdc++. More investigation is needed about this.
llvm-svn: 285526
This patch does two seperate things. First it adds a file called
"__libcpp_version" which only contains the current libc++ version
(currently 4000). This file is not intended for use as a header. This file
is used by Clang in order to easily determine the installed libc++ version.
This allows Clang to enable/disable certain language features only when the
library supports them.
The second change is the addition of _LIBCPP_LIBRARY_VERSION macro, which
returns the version of the installed dylib since it may be different than
the headers.
llvm-svn: 285382
Summary:
`__libcpp_refstring` currently has two different definitions. First there is the complete definition in `<__refstring>` but there is also a second in `<stdexcept>`. The historical reason for this split is because both libc++ and libc++abi need to see the inline definitions of __libcpp_refstrings methods, but the `<stdexcept>` header doesn't. However this is an ODR violation and breaks the modules build.
This patch fixes the issue by creating a single class definition in `<stdexcept>` and changing `<__refstring>` to contain only the inline method definitions. This way both `libcxx/src/stdexcept.cpp` and `libcxxabi/src/stdexcept.cpp` see the same declaration in `<stdexcept>` and definitions in `<__refstring>`
Reviewers: mclow.lists, EricWF
Subscribers: cfe-commits
Differential Revision: https://reviews.llvm.org/D25603
llvm-svn: 285100
Convert the Solaris xlocale.c compatibility library from plain C to C++
in order to fix the build failures caused by the addition of -std=c++11
to LIBCXX_COMPILE_FLAGS. The additional flag got propagated to the C
file, resulting in error with strict compilers.
Differential Revision: https://reviews.llvm.org/D25431
llvm-svn: 284494
Fix the iswxdigit_l() function prototype to take wint_t parameter
instead of incorrect wchar_t.
Differential Revision: https://reviews.llvm.org/D25431
llvm-svn: 284493
Summary:
This patch implements the library side of P0035R4. The implementation is thanks to @rsmith.
In addition to the C++17 implementation, the library implementation can be explicitly turned on using `-faligned-allocation` in all dialects.
Reviewers: mclow.lists, rsmith
Subscribers: rsmith, cfe-commits
Differential Revision: https://reviews.llvm.org/D25591
llvm-svn: 284206
These functions were removed from the dylib sometime between the 3.9 release
and now. This patch manually exports them to re-gain ABI compatibility.
llvm-svn: 284193
Summary:
Adapt implementation of Library Fundamentals TS optional into an implementation of N4606 optional.
- Update relational operators per http://wg21.link/P0307
- Update to requirements of http://wg21.link/P0032
- Extension: Implement trivial copy/move construction/assignment for `optional<T>` when `T` is trivially copyable.
Audit P/Rs for optional LWG issues:
- 2756 "C++ WP optional<T> should 'forward' T's implicit conversions" Implemented, which also resolves 2753 "Optional's constructors and assignments need constraints" (modulo my refusal to explicitly delete the move operations, which is a design error that I'm working on correcting in the 2756 P/R).
- 2736 "nullopt_t insufficiently constrained" Already conforming. I've added a test ensuring that `nullopt_t` is not copy-initializable from an empty braced-init-list, which I believe is the root intent of the issue, to avoid regression.
- 2740 "constexpr optional<T>::operator->" Already conforming.
- 2746 "Inconsistency between requirements for emplace between optional and variant" No P/R, but note that the author's '"suggested resolution" is already implemented.
- 2748 "swappable traits for optionals" Already conforming.
- 2753 "Optional's constructors and assignments need constraints" Implemented.
Most of the work for this patch was done by Casey Carter @ Microsoft. Thank you Casey!
Reviewers: mclow.lists, CaseyCarter, EricWF
Differential Revision: https://reviews.llvm.org/D22741
llvm-svn: 283980
This patch is largely thanks to Casey Carter @ Microsoft. He did the initial
work of porting our experimental implementation and tests over to namespace
std.
llvm-svn: 283977
Fuchsia is a new operating system which uses musl as the standard
C library, libc++ and libc++abi as the C++ standard library.
Differential Revision: https://reviews.llvm.org/D25414
llvm-svn: 283788
This patch applies the _LIBCPP_SAFE_STATIC attribute to internal globals,
most of which are locking primitives, in order to ensure that they can
safely be used during program startup.
This patch also fixes an unsafe static init issue with the global locks
used to implement atomic operations on shared pointers. Previously the
locks were initialized using a dynamically initialized pointer, so it was
possible that the pointer was uninitialized.
llvm-svn: 282640
The ::stat struct on Linux, FreeBSD, and OS X provides the access and
modification times as an instance of 'timespec', which has a nanosecond
resolution. The 'st_mtime' and 'st_atime' members simply reference the 'tv_sec'
value of the timespec struct. This patch changes 'last_write_time(...)' so that
it extracts both the seconds and nanoseconds values of the last modification
time, providing a more accurate implementation of 'last_write_time(...)'.
Additionally this patch fixes a possible signed integer overflow bug. The
'file_time_type' type cannot represent all possible values returned by
the filesystem. Attempting to construct a 'file_time_type' from one of these
values is undefined behavior. This patch avoids that UB by detecting possible
overflows before the conversion.
llvm-svn: 282634
Shoaib Meenai