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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