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libcxx fork for Darling build
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da6e915c73
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Eric Fiselier da6e915c73 Optimize operator=(const basic_string&) for tail call. 
Patch by Martijn Vels (mvels@google.com)
Reviewed as https://reviews.llvm.org/D68276

This is a non trivial win for externally templated assignment operator.

x86 without tail call (current libc++)

0000000000000000 <std::string::operator=(std::string const&)>:
   0:   55                      push   %rbp
   1:   48 89 e5                mov    %rsp,%rbp
   4:   53                      push   %rbx
   5:   50                      push   %rax
   6:   48 89 fb                mov    %rdi,%rbx
   9:   48 39 f7                cmp    %rsi,%rdi
   c:   74 17                   je     25 <std::string::operator=(std::string const&)+0x25>
   e:   0f b6 56 17             movzbl 0x17(%rsi),%edx
  12:   84 d2                   test   %dl,%dl
  14:   79 07                   jns    1d <std::string::operator=(std::string const&)+0x1d>
  16:   48 8b 56 08             mov    0x8(%rsi),%rdx
  1a:   48 8b 36                mov    (%rsi),%rsi
  1d:   48 89 df                mov    %rbx,%rdi
  20:   e8 00 00 00 00          callq  25 <std::string::operator=(std::string const&)+0x25>
  25:   48 89 d8                mov    %rbx,%rax
  28:   48 83 c4 08             add    $0x8,%rsp
  2c:   5b                      pop    %rbx
  2d:   5d                      pop    %rbp
  2e:   c3                      retq

After:

0000000000000000 <std::string::operator=(std::string const&)>:
   0:   48 39 f7                cmp    %rsi,%rdi
   3:   74 14                   je     19 <std::string::operator=(std::string const&)+0x19>
   5:   0f b6 56 17             movzbl 0x17(%rsi),%edx
   9:   84 d2                   test   %dl,%dl
   b:   79 07                   jns    14 <std::string::operator=(std::string const&)+0x14>
   d:   48 8b 56 08             mov    0x8(%rsi),%rdx
  11:   48 8b 36                mov    (%rsi),%rsi
  14:   e9 00 00 00 00          jmpq   19 <std::string::operator=(std::string const&)+0x19>
  19:   48 89 f8                mov    %rdi,%rax
  1c:   c3                      retq

Benchmark (pending per https://reviews.llvm.org/D67667)

```
BM_StringAssignStr_Empty_Opaque                     6.23ns ± 0%             5.19ns ± 0%  -16.70%          (p=0.016 n=5+4)
BM_StringAssignStr_Empty_Transparent                5.86ns ± 0%             5.14ns ± 0%  -12.24%          (p=0.008 n=5+5)
BM_StringAssignStr_Small_Opaque                     8.79ns ± 1%             7.69ns ± 0%  -12.53%          (p=0.008 n=5+5)
BM_StringAssignStr_Small_Transparent                9.44ns ± 0%             8.00ns ± 0%  -15.26%          (p=0.008 n=5+5)
BM_StringAssignStr_Large_Opaque                     25.2ns ± 0%             24.3ns ± 0%   -3.50%          (p=0.008 n=5+5)
BM_StringAssignStr_Large_Transparent                23.6ns ± 0%             22.5ns ± 0%   -4.76%          (p=0.008 n=5+5)
BM_StringAssignStr_Huge_Opaque                       319ns ± 5%              317ns ± 5%     ~             (p=0.690 n=5+5)
BM_StringAssignStr_Huge_Transparent                  319ns ± 5%              317ns ± 5%     ~             (p=0.421 n=5+5)
BM_StringAssignAsciiz_Empty_Opaque                  7.41ns ± 0%             7.77ns ± 0%   +4.89%          (p=0.008 n=5+5)
BM_StringAssignAsciiz_Empty_Transparent             7.54ns ± 3%             7.30ns ± 0%   -3.24%          (p=0.008 n=5+5)
BM_StringAssignAsciiz_Small_Opaque                  9.87ns ± 0%            10.24ns ± 1%   +3.76%          (p=0.008 n=5+5)
BM_StringAssignAsciiz_Small_Transparent             10.4ns ± 1%              9.8ns ± 2%   -5.78%          (p=0.008 n=5+5)
BM_StringAssignAsciiz_Large_Opaque                  30.1ns ± 0%             30.1ns ± 0%     ~             (p=0.167 n=5+5)
BM_StringAssignAsciiz_Large_Transparent             27.1ns ± 0%             27.4ns ± 0%   +0.92%          (p=0.016 n=4+5)
BM_StringAssignAsciiz_Huge_Opaque                    383ns ± 4%              382ns ± 4%     ~             (p=0.548 n=5+5)
BM_StringAssignAsciiz_Huge_Transparent               375ns ± 0%              380ns ± 0%   +1.37%          (p=0.029 n=4+4)
BM_StringAssignAsciizMix_Opaque                     14.0ns ± 0%             14.0ns ± 0%     ~             (p=0.881 n=5+5)
BM_StringAssignAsciizMix_Transparent                13.7ns ± 1%             13.8ns ± 0%     ~             (p=0.056 n=5+5)
```

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@374137 91177308-0d34-0410-b5e6-96231b3b80d8
2019-10-09 03:07:02 +00:00
benchmarks [libc++] Make sure we link all system libraries into the benchmarks 2019-10-08 16:26:24 +00:00
cmake [libc++] Workaround old versions of CMake that don't understand list(JOIN) 2019-10-08 21:33:35 +00:00
docs [NFC] Fix typos in libc++ documentation 2019-10-01 20:34:50 +00:00
fuzzing Update more file headers across all of the LLVM projects in the monorepo 2019-01-19 10:56:40 +00:00
include Optimize operator=(const basic_string&) for tail call. 2019-10-09 03:07:02 +00:00
lib [libc++] Add missing revision number in ABI changelog 2019-10-03 16:50:05 +00:00
src [libc++] Move the linker script generation step to CMake 2019-10-08 21:10:20 +00:00
test Add an off-by-default option to enable testing for gdb pretty printers. 2019-10-04 22:15:28 +00:00
utils [libc++] Move the linker script generation step to CMake 2019-10-08 21:10:20 +00:00
www [libc++] Take 2: Implement LWG 3158 2019-09-27 15:06:52 +00:00
.arcconfig [libcxx] Set up .arcconfig to point to new Diffusion CXX repository 2017-12-04 17:55:28 +00:00
.clang-format Make clang-format use C++03 syntax 2017-04-15 02:45:43 +00:00
.gitignore Implement N4606 optional 2016-10-12 07:46:20 +00:00
appveyor-reqs-install.cmd Attempt to upgrade compiler used by appveyor builds 2019-04-03 20:40:01 +00:00
appveyor.yml disable appveyor config for MSVC 2015 2019-04-03 20:36:51 +00:00
CMakeLists.txt [libc++] Move the linker script generation step to CMake 2019-10-08 21:10:20 +00:00
CREDITS.TXT Try again, this time with the correct address 2017-12-29 19:26:53 +00:00
LICENSE.TXT Fix typos throughout the license files that somehow I and my reviewers 2019-01-21 09:52:34 +00:00
NOTES.TXT Reland "Use custom command and target to install libc++ headers" 2018-06-12 03:10:02 +00:00
TODO.TXT Add list of filesystem NB comments to TODO.TXT so they can be tracked separately 2017-03-06 21:23:36 +00:00

docs/README.txt 

libc++ Documentation
====================

The libc++ documentation is written using the Sphinx documentation generator. It is
currently tested with Sphinx 1.1.3.

To build the documents into html configure libc++ with the following cmake options:

  * -DLLVM_ENABLE_SPHINX=ON
  * -DLIBCXX_INCLUDE_DOCS=ON

After configuring libc++ with these options the make rule `docs-libcxx-html`
should be available.