8fe7214fe2
--
406622c43f296eeedf00e0e9246acfb4ea6ecd5e by Abseil Team <absl-team@google.com>:
Avoid the compiler reloading __is_long() on string_view(const string&)
The underlying cause is that the compiler assume a scenario where string_view is created with placement new into memory occupied by the input, so the store to 'ptr' can affect the value / result of size(); i.e., __is_long() reloads the __size value).
Example code: string_view1 demonstrates the problem, string_view2 DTRT.
=== string_view1
struct string_view1 {
string_view1(const char* ptr, size_t n) : ptr(ptr), n(n) {}
string_view1(const std::string& s) : ptr(s.data()), n(s.length()) {}
const char* ptr;
size_t n;
};
struct S1 {
S1(const std::string& s);
string_view1 sv;
};
S1::S1(const std::string& s) : sv(s) {}
S1::S1
test byte ptr [rsi], 1
je .LBB0_1
mov rax, qword ptr [rsi + 16]
mov qword ptr [rdi], rax
movzx eax, byte ptr [rsi]
test al, 1
jne .LBB0_5
.LBB0_4:
shr rax
mov qword ptr [rdi + 8], rax
ret
.LBB0_1:
lea rax, [rsi + 1]
mov qword ptr [rdi], rax
movzx eax, byte ptr [rsi]
test al, 1
je .LBB0_4
.LBB0_5:
mov rax, qword ptr [rsi + 8]
mov qword ptr [rdi + 8], rax
ret
=== string_view2
struct string_view2 {
string_view2(const char* ptr, size_t n) : ptr(ptr), n(n) {}
string_view2(const std::string& s) : string_view2(s.data(), s.size()) {}
const char* ptr;
size_t n;
};
struct S2 {
S2(const std::string& s);
string_view2 sv;
};
S2::S2(const std::string& s) : sv(s) {}
S2::S2
movzx eax, byte ptr [rsi]
test al, 1
je .LBB1_1
mov rax, qword ptr [rsi + 8]
mov rsi, qword ptr [rsi + 16]
mov qword ptr [rdi], rsi
mov qword ptr [rdi + 8], rax
ret
.LBB1_1:
add rsi, 1
shr rax
mov qword ptr [rdi], rsi
mov qword ptr [rdi + 8], rax
ret
PiperOrigin-RevId: 272096771
GitOrigin-RevId: 406622c43f296eeedf00e0e9246acfb4ea6ecd5e
Change-Id: I70173a2db68cd9b597fff1c09e00198c632cfe95
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|---|---|---|
| absl | ||
| ci | ||
| CMake | ||
| .clang-format | ||
| .gitignore | ||
| ABSEIL_ISSUE_TEMPLATE.md | ||
| AUTHORS | ||
| CMakeLists.txt | ||
| conanfile.py | ||
| CONTRIBUTING.md | ||
| LICENSE | ||
| LTS.md | ||
| README.md | ||
| UPGRADES.md | ||
| WORKSPACE | ||
Abseil - C++ Common Libraries
The repository contains the Abseil C++ library code. Abseil is an open-source collection of C++ code (compliant to C++11) designed to augment the C++ standard library.
Table of Contents
About Abseil
Abseil is an open-source collection of C++ library code designed to augment the C++ standard library. The Abseil library code is collected from Google's own C++ code base, has been extensively tested and used in production, and is the same code we depend on in our daily coding lives.
In some cases, Abseil provides pieces missing from the C++ standard; in others, Abseil provides alternatives to the standard for special needs we've found through usage in the Google code base. We denote those cases clearly within the library code we provide you.
Abseil is not meant to be a competitor to the standard library; we've just found that many of these utilities serve a purpose within our code base, and we now want to provide those resources to the C++ community as a whole.
Quickstart
If you want to just get started, make sure you at least run through the Abseil Quickstart. The Quickstart contains information about setting up your development environment, downloading the Abseil code, running tests, and getting a simple binary working.
Building Abseil
Bazel is the official build system for Abseil, which is supported on most major platforms (Linux, Windows, macOS, for example) and compilers. See the quickstart for more information on building Abseil using the Bazel build system.
If you require CMake support, please check the CMake build instructions.
Codemap
Abseil contains the following C++ library components:
baseAbseil Fundamentals
Thebaselibrary contains initialization code and other code which all other Abseil code depends on. Code withinbasemay not depend on any other code (other than the C++ standard library).algorithm
Thealgorithmlibrary contains additions to the C++<algorithm>library and container-based versions of such algorithms.container
Thecontainerlibrary contains additional STL-style containers, including Abseil's unordered "Swiss table" containers.debugging
Thedebugginglibrary contains code useful for enabling leak checks, and stacktrace and symbolization utilities.hash
Thehashlibrary contains the hashing framework and default hash functor implementations for hashable types in Abseil.memory
Thememorylibrary contains C++11-compatible versions ofstd::make_unique()and related memory management facilities.meta
Themetalibrary contains C++11-compatible versions of type checks available within C++14 and C++17 versions of the C++<type_traits>library.numeric
Thenumericlibrary contains C++11-compatible 128-bit integers.strings
Thestringslibrary contains a variety of strings routines and utilities, including a C++11-compatible version of the C++17std::string_viewtype.synchronization
Thesynchronizationlibrary contains concurrency primitives (Abseil'sabsl::Mutexclass, an alternative tostd::mutex) and a variety of synchronization abstractions.time
Thetimelibrary contains abstractions for computing with absolute points in time, durations of time, and formatting and parsing time within time zones.types
Thetypeslibrary contains non-container utility types, like a C++11-compatible version of the C++17std::optionaltype.utility
Theutilitylibrary contains utility and helper code.
License
The Abseil C++ library is licensed under the terms of the Apache license. See LICENSE for more information.
Links
For more information about Abseil:
- Consult our Abseil Introduction
- Read Why Adopt Abseil to understand our design philosophy.
- Peruse our Abseil Compatibility Guarantees to understand both what we promise to you, and what we expect of you in return.