Commit Graph

64 Commits

Author SHA1 Message Date
Martijn Vels
c4b8c3ddc1 Add benchmarks for basic_string::erase
Reviewers: EricWF

Subscribers: christof, libcxx-commits

Tags: #libc

Differential Revision: https://reviews.llvm.org/D73740
2020-02-19 17:09:25 -05:00
Eric Fiselier
0c5102bd93 [libc++] Add additional benchmark functions to libcxx/benchmarks/string.bench
This change adds the following benchmarks:

- StringAssignStr
Assign a const basic::string& value

- StringAssignAsciiz
Assign a const char* asciiz value

StringAssignAsciizMix
Assign mixed long/short const char* asciiz values

- StringResizeDefaultInit
Resize default init benchmark

Patch by Martijn Vels (mvels@google.com)
Reviewed as D72343
2020-01-07 16:31:40 -05:00
Stephan T. Lavavej
7c9844b66e [libcxx][NFC] Strip trailing whitespace, fix typo. 2019-10-23 11:49:43 -07:00
Casey Carter
689ce81059
[libc++][NFC] Remove excess trailing newlines from most files
Testing git commit access.
2019-10-23 08:08:57 -07:00
Louis Dionne
32300877f9 [libc++] Make sure we link all system libraries into the benchmarks
It turns out that r374056 broke _some_ build bots again, specifically
the ones using sanitizers. Instead of trying to link the right system
libraries to the benchmarks bit-by-bit, let's just link exactly the
system libraries that libc++ itself needs.

llvm-svn: 374079
2019-10-08 16:26:24 +00:00
Louis Dionne
cf3ab6d96c [libc++] Add missing link-time dependencies to the benchmarks
Since the benchmarks build with -nostdlib, they need to manually link
against some system libraries that are used by the benchmarks and the
GoogleBenchmark library itself.

Previously, we'd rely on the fact that these libraries were linked
through the PUBLIC dependencies of cxx_shared/cxx_static. However,
if we were to make these dependencies PRIVATE (as they should be
because they are implementation details of libc++), the benchmarks
would fail to link. This commit remediates that.

llvm-svn: 374053
2019-10-08 14:28:56 +00:00
Louis Dionne
534c86d172 [libc++] Use PRIVATE to link benchmark dependencies
It's better style to use PRIVATE when linking libraries to executables,
and it doesn't make a difference since executables don't need to propagate
their link-time dependencies anyway.

llvm-svn: 374050
2019-10-08 14:10:55 +00:00
Louis Dionne
c5b74bf6e5 [libc++] Add a per-target flag to include the generated config_site
This allows propagating the include automatically to targets that
depend on one of the libc++ targets such as the benchmarks. Note
that the GoogleBenchmark build itself still needs to manually specify
the -include, since I don't know of any way to have an external project
link against one of the libc++ targets (which would propagate the -include
automatically).

llvm-svn: 373631
2019-10-03 17:20:50 +00:00
Nico Weber
f938755a33 libcxx: Rename .hpp files in libcxx/benchmarks to .h
LLVM uses .h as its extension for header files.

Differential Revision: https://reviews.llvm.org/D66509

llvm-svn: 369487
2019-08-21 01:59:12 +00:00
Eric Fiselier
a6edef3563 Attempt to fix MSAN failures in benchmarks
llvm-svn: 369482
2019-08-21 00:14:48 +00:00
Nico Weber
cc89063bff libcxx: Rename .hpp files in libcxx/test/support to .h
LLVM uses .h as its extension for header files.

Files renamed using:

    for f in libcxx/test/support/*.hpp; do git mv $f ${f%.hpp}.h; done

References to the files updated using:

    for f in $(git diff master | grep 'rename from' | cut -f 3 -d ' '); do
        a=$(basename $f);
        echo $a;
        rg -l $a libcxx | xargs sed -i '' "s/$a/${a%.hpp}.h/";
    done

HPP include guards updated manually using:

    for f in $(git diff master | grep 'rename from' | cut -f 3 -d ' '); do
      echo ${f%.hpp}.h ;
    done | xargs mvim

Differential Revision: https://reviews.llvm.org/D66104

llvm-svn: 369481
2019-08-21 00:14:12 +00:00
Eric Fiselier
b0945e1bd2 Improve codegen for deque.
This patch rewrites a few loops in deque and split_buffer to better
optimize the codegen. For constructors like
`deque<unsigned char> d(500000, 0);` this patch results in a 2x speedup.

The patch improves the codegen  in roughly three ways:

1. Changes do { ... } while (...) loops into more typical for loops.
  The optimizer can reason about normal looking loops better.

2. Split the iteration over a range into (A) iteration over the blocks,
then (B) iteration within the block. This nested structure helps LLVM
lower the inner loop to `memset`.

3. Do fewer things each iteration. Some of these loops were incrementing
  or changing 4-5 variables every loop (in addition to the
  construction). Previously most loops would increment the end pointer,
  the size, and decrement the count of remaining items to construct.
  Now we only increment a single pointer for most iterations.

llvm-svn: 368547
2019-08-12 07:51:05 +00:00
Eric Fiselier
c4952da401 Add benchmarks to test the cost of allocator
llvm-svn: 367722
2019-08-02 21:13:38 +00:00
Eric Fiselier
d4ace50ed0 Fix PR35637: suboptimal codegen for vector<unsigned char>.
The optimizer is petulant and temperamental. In this case LLVM failed to lower
the the "insert at end" loop used by`vector<unsigned char>` to a `memset` despite
`memset` being substantially faster over a range of bytes.

LLVM has the ability to lower loops to `memset` whet appropriate, but the
odd nature of libc++'s loops prevented the optimization from taking places.

This patch addresses the issue by rewriting the loops from the form
`do [ ... --__n; } while (__n > 0);` to instead use a for loop over a pointer
range (For example: `for (auto *__i = ...; __i < __e; ++__i)`).

This patch also rewrites the asan annotations to unposion all additional memory
at the start of the loop instead of once per iterations. This could potentially
permit false negatives where the constructor of element N attempts to access
element N + 1 during its construction.

The before and after results for the `BM_ConstructSize/vector_byte/5140480_mean`
benchmark (run 5 times) are:

--------------------------------------------------------------------------------------------
Benchmark                                                 Time             CPU   Iterations
--------------------------------------------------------------------------------------------
Before
------
BM_ConstructSize/vector_byte/5140480_mean          12530140 ns     12469693 ns            N/A
BM_ConstructSize/vector_byte/5140480_median        12512818 ns     12445571 ns            N/A
BM_ConstructSize/vector_byte/5140480_stddev          106224 ns       107907 ns            5
-----
After
-----
BM_ConstructSize/vector_byte/5140480_mean            167285 ns       166500 ns            N/A
BM_ConstructSize/vector_byte/5140480_median          166749 ns       166069 ns            N/A
BM_ConstructSize/vector_byte/5140480_stddev            3242 ns         3184 ns            5

llvm-svn: 367183
2019-07-28 04:37:02 +00:00
Louis Dionne
68924e6be7 [libc++][CMake] Refactor how we link against system libraries
Summary:
Instead of populating the global LIBCXX_LIBRARIES, we use the link-time
dependency management built into CMake to propagate link flags. This
leads to a cleaner and easier-to-follow build.

Reviewers: phosek, smeenai, EricWF

Subscribers: mgorny, christof, jkorous, dexonsmith, jfb, mstorsjo, libcxx-commits

Tags: #libc

Differential Revision: https://reviews.llvm.org/D60969

llvm-svn: 359571
2019-04-30 15:44:19 +00:00
Samuel Benzaquen
27a83e99f4 Add more benchmarks for literal strings.
Summary:
Comparing against the empty string should generate much better code that
what it does today.
We can also generate better code when comparing against literals that
are larger than the SSO space.

Reviewers: EricWF

Subscribers: christof, jdoerfert, libcxx-commits

Tags: #libc

Differential Revision: https://reviews.llvm.org/D59781

llvm-svn: 357614
2019-04-03 17:40:51 +00:00
Samuel Benzaquen
9b7aa02b53 Add relational benchmark against a string constant.
Summary:
Add relational benchmark against a string constant.
These can potentially trigger inlining of the operations. We want to
benchmark that.

Reviewers: EricWF

Subscribers: christof, jdoerfert, libcxx-commits

Tags: #libc

Differential Revision: https://reviews.llvm.org/D59512

llvm-svn: 356680
2019-03-21 16:06:15 +00:00
Louis Dionne
cc37af7a36 [libc++] Build <filesystem> support as part of the dylib
Summary:
This patch treats <filesystem> as a first-class citizen of the dylib,
like all other sub-libraries (e.g. <chrono>). As such, it also removes
all special handling for installing the filesystem library separately
or disabling part of the test suite from the lit command line.

Unlike the previous attempt (r356500), this doesn't remove all the
filesystem tests.

Reviewers: mclow.lists, EricWF, serge-sans-paille

Subscribers: mgorny, christof, jkorous, dexonsmith, jfb, jdoerfert, libcxx-commits

Differential Revision: https://reviews.llvm.org/D59152

llvm-svn: 356518
2019-03-19 20:56:13 +00:00
Louis Dionne
f7b43230b8 Revert "[libc++] Build <filesystem> support as part of the dylib"
When I applied r356500 (https://reviews.llvm.org/D59152), I somehow
deleted all of filesystem's tests. I will revert r356500 and re-apply
it properly.

llvm-svn: 356505
2019-03-19 19:27:29 +00:00
Louis Dionne
72122d058b [libc++] Build <filesystem> support as part of the dylib
Summary:
This patch treats <filesystem> as a first-class citizen of the dylib,
like all other sub-libraries (e.g. <chrono>). As such, it also removes
all special handling for installing the filesystem library separately
or disabling part of the test suite from the lit command line.

Reviewers: mclow.lists, EricWF, serge-sans-paille

Subscribers: mgorny, christof, jkorous, dexonsmith, jfb, jdoerfert, libcxx-commits

Differential Revision: https://reviews.llvm.org/D59152

llvm-svn: 356500
2019-03-19 19:09:33 +00:00
Petr Hosek
8e78915446 [CMake] Use correct visibility for linked libraries in CMake
When linking library dependencies, we shouldn't need to export linked
libraries to dependents. We should be explicit about this in
target_link_libraries, otherwise other targets that depend on these such
as sanitizers get repeated (and possibly even conflicting) dependencies.

Differential Revision: https://reviews.llvm.org/D57456

llvm-svn: 352688
2019-01-30 23:18:05 +00:00
Chandler Carruth
57b08b0944 Update more file headers across all of the LLVM projects in the monorepo
to reflect the new license. These used slightly different spellings that
defeated my regular expressions.

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: 351648
2019-01-19 10:56:40 +00:00
Louis Dionne
04695a7539 [libcxx] Speeding up partition_point/lower_bound/upper_bound
This is a re-application of r345525, which had been reverted by fear of
a regression.

Reviewed as https://reviews.llvm.org/D53994.
Thanks to Denis Yaroshevskiy for the patch.

llvm-svn: 349358
2018-12-17 16:04:39 +00:00
Samuel Benzaquen
06a9b5a305 Add benchmarks for sorting and heap functions.
Summary:
Benchmarks for std::sort, std::stable_sort, std::make_heap,
std::sort_heap, std::pop_heap and std::push_heap.

The benchmarks are run with integers and strings, and with different
sorted input.

Reviewers: EricWF

Subscribers: christof, mgrang, ldionne, libcxx-commits

Differential Revision: https://reviews.llvm.org/D53978

llvm-svn: 347329
2018-11-20 17:15:17 +00:00
Eric Fiselier
aacebba5e6 Disable filesystem benchmark when libstdc++ doesn't support it
llvm-svn: 346989
2018-11-15 19:53:43 +00:00
Eric Fiselier
0997403a22 propagate __config_site includes when building benchmarks
llvm-svn: 346933
2018-11-15 07:29:56 +00:00
Eric Fiselier
5828115e58 Attempt to show progress bar in benchmark tests
llvm-svn: 346905
2018-11-14 22:49:42 +00:00
Eric Fiselier
1dbe7ec946 Exclude check-cxx-benchmarks from the global test target.
llvm-svn: 346904
2018-11-14 22:48:43 +00:00
Eric Fiselier
336a1a6811 Rename cxx-benchmark-unittests target and convert to LIT.
This patch renames the cxx-benchmark-unittests to check-cxx-benchmarks
and converts the target to use LIT in order to make the tests run faster
and provide better output.

In particular this runs each benchmark in a suite one by one, allowing
more parallelism while ensuring output isn't garbage with multiple threads.

Additionally, it adds the CMake flag '-DLIBCXX_BENCHMARK_TEST_ARGS=<list>'
to specify what options are passed when running the benchmarks.

llvm-svn: 346888
2018-11-14 20:38:46 +00:00
Eric Fiselier
02f8e7c355 Add cxx-benchmark-unittests target
This patch adds the cxx-benchmark-unittests target so we can start
getting test coverage on the benchmarks, including building with
sanitizers. Because we're only looking for test-coverage, the benchmarks
run for the shortest time possible, and in parallel.

The target is excluded from all by default. It only
builds and runs the libcxx configurations of the benchmarks, and not
any versions built against the systems native standard library.

llvm-svn: 346811
2018-11-13 23:08:31 +00:00
Eric Fiselier
9039b6012e Fix "use of" uninitialized memory in benchmark.
An argument to DoNotOptimize was not fully initialized, which caused
msan to complain.

llvm-svn: 346808
2018-11-13 23:00:55 +00:00
Eric Fiselier
3bea50aeb3 Fix UB in string.bench.cpp.
The usage of aligned_storage failed to pass the alignment it wanted,
which caused it to have a larger size and alignment that the
std::string's it was intended to store.

This patch manually specifies the alignment, as well as cleaning up
type alias bugs.

llvm-svn: 346779
2018-11-13 19:16:19 +00:00
Eric Fiselier
4de1c753ff Attempt to make benchmarks fall back to -std=c++1z when C++17 isn't supported.
The benchmarks currently require C++17, however Clang 3.9 doesn't
support -std=c++17 while still supporting all the C++17 features needed
to compile the benchmarks.

This patch makes the benchmark build attempt to fall back to -std=c++1z
when -std=c++17 isn't supported.

See llvm.org/PR39629

llvm-svn: 346744
2018-11-13 07:03:16 +00:00
Louis Dionne
e0a724ef9c Revert "Bug 39129: Speeding up partition_point/lower_bound/upper_bound/ by using unsigned division by 2 when possible."
This reverts r345525. I'm reverting because that patch apparently caused
a regression on certain platforms (see https://reviews.llvm.org/D53994).
Since we don't fully understand the reasons for the regression, I'm
reverting until we can provide a fix we understand.

llvm-svn: 345893
2018-11-01 21:24:32 +00:00
Samuel Benzaquen
74583444e7 Add more benchmarks for std::string.
Summary:
Added benchmarks for Construct, Copy, Move, Destroy, Relationals and
Read. On the ones that matter, the benchmarks tests hot and cold data,
and opaque and transparent inputs.

Reviewers: EricWF

Subscribers: christof, ldionne, libcxx-commits

Differential Revision: https://reviews.llvm.org/D53825

llvm-svn: 345611
2018-10-30 15:54:22 +00:00
Eric Fiselier
8c40d81d4f Bug 39129: Speeding up partition_point/lower_bound/upper_bound/ by using unsigned division by 2 when possible.
Patch by Denis Yaroshevskiy (denis.yaroshevskij@gmail.com)

The rational and measurements can be found in the bug description: https://bugs.llvm.org/show_bug.cgi?id=39129

Reviewed as https://reviews.llvm.org/D52697

llvm-svn: 345525
2018-10-29 19:25:02 +00:00
Samuel Benzaquen
2f628a1030 Fix mismatch between size_t and uint64_t in std::set benchmark.
llvm-svn: 345523
2018-10-29 19:08:31 +00:00
Samuel Benzaquen
37632992ef Add benchmark for std::set.
Summary:
Benchmarks for construct, find, insert and iterate, with sequential
and random ordered inputs.

It also improves the cartesian product benchmark header to allow for
runtime values to be specified in the product.

Reviewers: EricWF

Subscribers: christof, ldionne, libcxx-commits

Differential Revision: https://reviews.llvm.org/D53523

llvm-svn: 345035
2018-10-23 14:49:27 +00:00
Samuel Benzaquen
0e6a833e46 Add benchmarks for std::function.
Summary:
Benchmarks for construct, copy, move, swap, destroy and invoke, with 8
different input states.
For the cases that matter, it tests with and without allowing constant
value propagation from construction into the operation tested.

This also adds helper functions to generate the cartesian product of
different configurations and generate benchmarks for all of them.

Reviewers: EricWF

Subscribers: christof, ldionne, libcxx-commits

Differential Revision: https://reviews.llvm.org/D53087

llvm-svn: 344415
2018-10-12 21:01:15 +00:00
Eric Fiselier
fca28db904 Add test macros for always_inline and noinline
llvm-svn: 344167
2018-10-10 18:22:23 +00:00
Eric Fiselier
5ac4e51d53 Fix linking filesystem benchmarks
llvm-svn: 344160
2018-10-10 17:46:20 +00:00
Eric Fiselier
09701324a1 Add new string benchmarks
llvm-svn: 336636
2018-07-10 04:11:22 +00:00
Eric Fiselier
d7fae181c3 Implement filesystem NB comments, relative paths, and related issues.
This is a fairly large patch that implements all of the filesystem NB comments
and the relative paths changes (ex. adding weakly_canonical). These issues
and papers are all interrelated so their implementation couldn't be split up
nicely.

This patch upgrades <experimental/filesystem> to match the C++17 spec and not
the published experimental TS spec. Some of the changes in this patch are both
API and ABI breaking, however libc++ makes no guarantee about stability for
experimental implementations.

The major changes in this patch are:

* Implement NB comments for filesystem (P0492R2), including:
  * Implement `perm_options` enum as part of NB comments, and update the
    `permissions` function to match.
  * Implement changes to `remove_filename` and `replace_filename`
  * Implement changes to `path::stem()` and `path::extension()` which support
    splitting examples like `.profile`.
  * Change path iteration to return an empty path instead of '.' for trailing
    separators.
  * Change `operator/=` to handle absolute paths on the RHS.
  * Change `absolute` to no longer accept a current path argument.

* Implement relative paths according to NB comments (P0219r1)

* Combine `path.cpp` and `operations.cpp` since some path functions require
  access to the operations internals, and some fs operations require access
  to the path parser.

llvm-svn: 329028
2018-04-02 23:03:41 +00:00
Eric Fiselier
1903976d37 Update Google Benchmark library
llvm-svn: 322812
2018-01-18 04:23:01 +00:00
Stephan T. Lavavej
4d8a75a1ca [libcxx] [test] Fix line endings, avoid unnecessary non-ASCII.
benchmarks/util_smartptr.bench.cpp
Change CRLF to LF.

test/std/localization/locale.categories/category.monetary/locale.money.get/locale.money.get.members/get_long_double_fr_FR.pass.cpp
Consistently comment "\u20ac" as EURO SIGN, its Unicode name, instead of the actual Unicode character.

test/std/utilities/allocator.adaptor/allocator.adaptor.members/construct_type.pass.cpp
Avoid non-ASCII dash.

Fixes D40991.

llvm-svn: 320536
2017-12-13 00:51:31 +00:00
Aditya Kumar
38bc3df8a3 [locale] Avoid copy of __atoms when char_type is char
The function num_get<_CharT>::stage2_int_prep makes unnecessary copy of src
into atoms when char_type is char. This can be avoided by creating
a switch on type and just returning __src when char_type is char.

Added the test case to demonstrate performance improvement.
In order to avoid ABI incompatibilities, the changes are guarded
with a macro _LIBCPP_ABI_OPTIMIZED_LOCALE_NUM_GET

Differential Revision: https://reviews.llvm.org/D30268
Reviewed by: EricWF

llvm-svn: 305427
2017-06-14 23:17:45 +00:00
Eric Fiselier
74619721a9 Emit benchmark tests into the benchmarks build directory, not lib/
llvm-svn: 300533
2017-04-18 07:40:22 +00:00
Sebastian Pop
9070500633 improve performance of string::find
string::find used to call the generic algorithm ::find.  The patch special
case string::find such that it ultimately gets converted to calls to memchr
and memcmp.

The patch improves the performance of the string::find routine by about 20x.

Without the patch, the performance on an x86_64-linux 3400 MHz machine is:

Benchmark                           Time           CPU Iterations
-----------------------------------------------------------------
BM_StringFindNoMatch/10             4 ns          4 ns  166421326
BM_StringFindNoMatch/64            37 ns         37 ns   18754392
BM_StringFindNoMatch/512          268 ns        268 ns    2586060
BM_StringFindNoMatch/4k          2143 ns       2144 ns     328342
BM_StringFindNoMatch/32k        16910 ns      16917 ns      40623
BM_StringFindNoMatch/128k       67577 ns      67602 ns      10138
BM_StringFindAllMatch/1             3 ns          3 ns  265163471
BM_StringFindAllMatch/8             6 ns          6 ns  112582467
BM_StringFindAllMatch/64           36 ns         36 ns   19566457
BM_StringFindAllMatch/512         209 ns        209 ns    3318893
BM_StringFindAllMatch/4k         1618 ns       1618 ns     432963
BM_StringFindAllMatch/32k       12909 ns      12914 ns      54317
BM_StringFindAllMatch/128k      48342 ns      48361 ns      13922
BM_StringFindMatch1/1           33777 ns      33790 ns      20698
BM_StringFindMatch1/8           33940 ns      33953 ns      20619
BM_StringFindMatch1/64          34038 ns      34051 ns      20571
BM_StringFindMatch1/512         34217 ns      34230 ns      20480
BM_StringFindMatch1/4k          35510 ns      35524 ns      19752
BM_StringFindMatch1/32k         46438 ns      46456 ns      15030
BM_StringFindMatch2/1           33839 ns      33852 ns      20648
BM_StringFindMatch2/8           33950 ns      33963 ns      20594
BM_StringFindMatch2/64          33846 ns      33859 ns      20668
BM_StringFindMatch2/512         34023 ns      34036 ns      20279
BM_StringFindMatch2/4k          35422 ns      35436 ns      19716
BM_StringFindMatch2/32k         46570 ns      46588 ns      15027

With the patch applied

Benchmark                           Time           CPU Iterations
-----------------------------------------------------------------
BM_StringFindNoMatch/10             5 ns          5 ns  133724346
BM_StringFindNoMatch/64             6 ns          6 ns  119312184
BM_StringFindNoMatch/512           13 ns         13 ns   51539628
BM_StringFindNoMatch/4k            77 ns         77 ns    8935934
BM_StringFindNoMatch/32k          551 ns        551 ns    1222808
BM_StringFindNoMatch/128k        2684 ns       2685 ns     259957
BM_StringFindAllMatch/1             7 ns          7 ns   98017959
BM_StringFindAllMatch/8             7 ns          7 ns   91466911
BM_StringFindAllMatch/64            8 ns          8 ns   85707392
BM_StringFindAllMatch/512          20 ns         20 ns   34490895
BM_StringFindAllMatch/4k           93 ns         93 ns    7360375
BM_StringFindAllMatch/32k         827 ns        828 ns     829944
BM_StringFindAllMatch/128k       3593 ns       3594 ns     195815
BM_StringFindMatch1/1            1332 ns       1332 ns     516354
BM_StringFindMatch1/8            1336 ns       1336 ns     495876
BM_StringFindMatch1/64           1338 ns       1339 ns     516656
BM_StringFindMatch1/512          1357 ns       1357 ns     510717
BM_StringFindMatch1/4k           1485 ns       1486 ns     461228
BM_StringFindMatch1/32k          2235 ns       2236 ns     318253
BM_StringFindMatch2/1            1335 ns       1335 ns     517105
BM_StringFindMatch2/8            1336 ns       1337 ns     518004
BM_StringFindMatch2/64           1344 ns       1345 ns     511751
BM_StringFindMatch2/512          1361 ns       1361 ns     508150
BM_StringFindMatch2/4k           1611 ns       1611 ns     463388
BM_StringFindMatch2/32k          2187 ns       2187 ns     317532

Patch written by Aditya Kumar and Sebastian Pop.

Differential Revision: https://reviews.llvm.org/D27068

llvm-svn: 290761
2016-12-30 18:01:36 +00:00
Eric Fiselier
a55333003d Optimize filesystem::path by providing weaker exception guarantees.
path uses string::append to construct, append, and concatenate paths. Unfortunatly
string::append has a strong exception safety guaranteed and if it can't prove
that the iterator operations don't throw then it will allocate a temporary
string copy to append to. However this extra allocation and copy is very
undesirable for path which doesn't have the same exception guarantees.

To work around this this patch adds string::__append_forward_unsafe which exposes
the std::string::append interface for forward iterators without enforcing
that the iterator is noexcept.

llvm-svn: 285532
2016-10-31 02:46:25 +00:00
Eric Fiselier
ef915d3ef4 Improve performance of constructing filesystem::path from strings.
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
2016-10-30 23:53:50 +00:00