[PATCH] D56593: [SelectionDAG][RFC] Allow the user to specify a memeq function (v5).

[Clement Courbet via Phabricator via llvm-commits]

courbet added a comment.

In D56593#1448298 <https://reviews.llvm.org/D56593#1448298>, @thakis wrote:

> This made pdfium use 6.8% more cpu, https://bugs.chromium.org/p/chromium/issues/detail?id=947611
>
> Since the intent here was to make things faster, any ideas how this could happen?


Hi Nico, thanks for reporting.

This commit introduced a regression (https://bugs.llvm.org/show_bug.cgi?id=40699): memcmp with small constant sizes, e.g. `memcmp(a, b, 16) == 0`, was expanded as `bcmp(a, b, 16) == 0` instead of being lowered to two loads + 1 compare.

This was fixed in https://reviews.llvm.org/rL356550

Could that be the reason for the regression ? I've tried reproducing with the commands in https://bugs.chromium.org/p/chromium/issues/detail?id=947611, but my valgrind will not handle AVX instructions:

  valgrind: Unrecognised instruction at address 0x4015cc9
     at 0x4015CC9: _dl_runtime_resolve_avx_slow
  ...




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