[all-commits] [llvm/llvm-project] dda107: Revert "[libc][bazel] Enable software prefetching ...

[Guillaume Chatelet via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: dda107b8cb7cb35690a45518c72f85a1df04be1a
      https://github.com/llvm/llvm-project/commit/dda107b8cb7cb35690a45518c72f85a1df04be1a
  Author: Guillaume Chatelet <gchatelet at google.com>
  Date:   2024-10-07 (Mon, 07 Oct 2024)

  Changed paths:
    M utils/bazel/llvm-project-overlay/libc/libc_configure_options.bzl

  Log Message:
  -----------
  Revert "[libc][bazel] Enable software prefetching for memcpy" (#111370)

Reverts llvm/llvm-project#108939

When `AVX` is available but `-mprefer-vector-width=128` some of the
`mov` instructions turn into the x86 `rep;movsb` instruction leading to
poor performance on "old" architectures (sandybridge, haswell). The
possible solutions are : get rid of the `-mprefer-vector-width` option
or use smaller static copy sizes in
`inline_memcpy_x86_sse2_ge64_sw_prefetching`. Right now a copy size of 3
cache lines (192B) relying exclusively on xmm registers gets turned into
`rep;movsb`.



To unsubscribe from these emails, change your notification settings at https://github.com/llvm/llvm-project/settings/notifications