forked from OSchip/llvm-project
353fbd3516
Using fwrite and fread was very *very* slow. The resulting code was multiple times slower than GCC's implementation of gcov. Replace the fwrite/fread system with an mmap() version. If the `.gcda' file doesn't exist, we (re)allocate a buffer that we write into. That gets written to the `.gcda' file in one chunk. If the `.gcda' file already exists, we simply mmap() the file, modify the mapped data, and use msync() to write the contents out to disk. It's much easier than implementing our own buffering scheme, and we don't have to use fwrite's and fread's buffering. For those who are numbers-oriented, here are some timings: GCC Verison ----------- `.gcda' files don't exist: 23s `.gcda' files do exist: 14s LLVM Version (before this change) --------------------------------- `.gcda' files don't exist: 28s `.gcda' files do exist: 28s LLVM Version (with this change) ------------------------------- `.gcda' files don't exist: 18s `.gcda' files do exist: 4s It's a win-win-win-win-lose-win-win scenario! <rdar://problem/13466086> llvm-svn: 182563 |
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| README.txt | ||
README.txt
It is often convenient to be able to build compiler-rt libraries for a certain platform without having a full SDK or development environment installed. This makes it easy for users to build a compiler which can target a number of different platforms, without having to actively maintain full development environments for those platforms. Since compiler-rt's libraries typically have minimal interaction with the system, we achieve this by stubbing out the SDKs of certain platforms.