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For machines with a lot of cores, hardware prefetchers can saturate the memory bus when utilization is high. In this case it is desirable to turn off the hardware prefetcher completely. This has a big impact on the performance of memory functions such as `memcpy` that rely on the fact that the next cache line will be readily available. This patch adds the 'LIBC_COPT_MEMCPY_X86_USE_SOFTWARE_PREFETCHING' compile time option that generates a version of memcpy with software prefetching. While not fully restoring the original performances it mitigates the impact to an acceptable level. Reviewed By: rtenneti Differential Revision: https://reviews.llvm.org/D154494
LLVM libc ========= This directory and its subdirectories contain source code for llvm-libc, a retargetable implementation of the C standard library. LLVM is open source software. You may freely distribute it under the terms of the license agreement found in LICENSE.txt.