Martijn Vels 2bad222680 Add optimization to basic_string::assign for compile-time known constant values. ... Summary: This change optimizes the assign() methods for string where either the contents or lengths are compile time known constants. For small strings (< min_cap) we can execute the assignment entirely inline. For strings up to 128 bytes we allow the compiler to efficiently inline the copy operation after we call the offline __resize<>() method. Short / long branches are taken at the call site for better branch prediction and allowing FDO optimizations. Benchmarks (unstable / google perflab): ``` name old time/op new time/op delta BM_StringAssignAsciiz_Empty_Opaque 5.69ns ± 7% 5.97ns ± 7% ~ (p=0.056 n=5+5) BM_StringAssignAsciiz_Empty_Transparent 5.39ns ± 7% 0.79ns ± 8% -85.36% (p=0.008 n=5+5) BM_StringAssignAsciiz_Small_Opaque 11.2ns ± 5% 11.0ns ± 6% ~ (p=0.548 n=5+5) BM_StringAssignAsciiz_Small_Transparent 10.1ns ± 7% 1.0ns ± 8% -89.76% (p=0.008 n=5+5) BM_StringAssignAsciiz_Large_Opaque 23.5ns ± 7% 23.8ns ± 7% ~ (p=0.841 n=5+5) BM_StringAssignAsciiz_Large_Transparent 21.4ns ± 7% 12.7ns ± 7% -40.83% (p=0.008 n=5+5) BM_StringAssignAsciiz_Huge_Opaque 336ns ± 4% 327ns ± 7% ~ (p=0.421 n=5+5) BM_StringAssignAsciiz_Huge_Transparent 331ns ± 5% 324ns ± 7% ~ (p=0.548 n=5+5) BM_StringAssignAsciizMix_Opaque 13.6ns ±10% 13.7ns ± 9% ~ (p=0.690 n=5+5) BM_StringAssignAsciizMix_Transparent 12.9ns ± 8% 3.6ns ± 8% -71.82% (p=0.008 n=5+5) ``` Reviewers: EricWF, #libc! Subscribers: jfb, libcxx-commits Tags: #libc Differential Revision: https://reviews.llvm.org/D82221		2020-06-29 14:34:34 -04:00
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benchmarks	[libc++] Always generate a __config_site header	2020-06-26 00:47:48 -04:00
cmake	[libc++] Enable tests and documentation by default when building standalone	2020-06-29 12:40:07 -04:00
docs	[libc++] Provide a default LLVM_PATH when building standalone	2020-06-29 12:40:07 -04:00
fuzzing	[libc++] Tolerate NaN returning random distributions for now	2019-12-12 17:11:13 -05:00
include	Add optimization to basic_string::assign for compile-time known constant values.	2020-06-29 14:34:34 -04:00
lib	Add optimization to basic_string::assign for compile-time known constant values.	2020-06-29 14:34:34 -04:00
src	[libc++] Remove workarounds for the lack of clock_gettime on older macOS platforms	2020-06-09 12:57:03 -04:00
test	[runtimes] Remove the ability to select the old libc++ testing format	2020-06-29 14:07:41 -04:00
utils	[runtimes] Remove the ability to select the old libc++ testing format	2020-06-29 14:07:41 -04:00
www	[libc++] Implement <numbers>	2020-06-19 14:25:02 +05:30
.clang-format	…
.gitignore	[libcxx] Fix .gitignore to not exclude test directories	2020-03-25 17:52:23 -07:00
CMakeLists.txt	[libc++] Do not try creating llvm-lit when LIBCXX_INCLUDE_TESTS is OFF in the standalone build	2020-06-29 11:55:02 -04:00
CREDITS.TXT	[libcxx] Adds [concept.same]	2020-04-08 18:00:13 -04:00
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	…
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