本文主要是介绍LLVM libc++的RISCV支持，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
libc++的官方主页：http://libcxx.llvm.org/
libc++文档主页：https://libcxx.llvm.org/docs/
简介：
libc++ is an implementation of the C++ standard library, targeting C++11, C++14 and above.
All of the code in libc++ is dual licensed under the MIT license and the UIUC License (a BSD-like license).
对标的产品：
1、 Apache's libstdcxx
2、GNU's libstdc++
3、STLport
目前状态：（来源：http://libcxx.llvm.org/ 和 https://libcxx.llvm.org/docs/）
1、操作系统和硬件平台支持状况
libc++ is known to work on the following platforms, using gcc and clang. (Note that functionality provided by <atomic> is only functional with clang and gcc.)
2、编译器版本支持
- Clang 4.0 and above
- GCC 5.0 and above.
The C++03 dialect is only supported for Clang compilers.
3、C++版本支持情况
- C++11 - Complete
- C++14 - Complete（http://libcxx.llvm.org/cxx1y_status.html）
- C++17 - In Progress（http://libcxx.llvm.org/cxx1z_status.html）
- C++2a - In Progress（http://libcxx.llvm.org/cxx2a_status.html）
- Post C++14 Technical Specifications - In Progress（http://libcxx.llvm.org/ts1z_status.html）
- C++ Feature Test Macro Status（https://libcxx.llvm.org/docs/FeatureTestMacroTable.html#feature-status）
编译与测试：（来源：https://libcxx.llvm.org/docs/BuildingLibcxx.html#getting-started）
$ git clone https://github.com/llvm/llvm-project.git
$ cd llvm-project $ mkdir build && cd build
$ cmake -DCMAKE_C_COMPILER=clang \ -DCMAKE_CXX_COMPILER=clang++ \ -DLLVM_ENABLE_PROJECTS="libcxx;libcxxabi" \ ../llvm
$ make # Build $ make check-cxx # Test
$ make install-cxx install-cxxabi # Install
注意：make check-cxx 无法执行，执行llvm-lit libcxx/test/目录，得到结果：
源码中与RISC-V相关的内容：
1、/libcxx/utils/google-benchmark/src/cycleclock.h中有关于riscv架构时钟的一些内容：
#elif defined(__riscv) // RISC-V// Use RDCYCLE (and RDCYCLEH on riscv32)
#if __riscv_xlen == 32uint32_t cycles_lo, cycles_hi0, cycles_hi1;// This asm also includes the PowerPC overflow handling strategy, as above.// Implemented in assembly because Clang insisted on branching.asm volatile("rdcycleh %0\n""rdcycle %1\n""rdcycleh %2\n""sub %0, %0, %2\n""seqz %0, %0\n""sub %0, zero, %0\n""and %1, %1, %0\n": "=r"(cycles_hi0), "=r"(cycles_lo), "=r"(cycles_hi1));return (static_cast<uint64_t>(cycles_hi1) << 32) | cycles_lo;
#elseuint64_t cycles;asm volatile("rdcycle %0" : "=r"(cycles));return cycles;
#endif
发布于 10:17
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