[PATCH] D56593: [SelectionDAG][RFC] Allow the user to specify a memeq function (v5).
Clement Courbet via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Mon Apr 1 01:17:53 PDT 2019
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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