[flac-dev] [PATCH] cpu.h: add defines for clang
lvqcl.mail at gmail.com
Sun Feb 12 11:27:41 UTC 2017
Erik de Castro Lopo wrote:
> How reliable a test is that? I do 99.9% of my dev work on a laptop
> and whenever I need to benchmark something I need to do so on a
> desketop machine because the laptop doesn't give consistent results.
About 1.5 years ago I tested AVX2 speed increase on Haswell (i7-4770)
using -8 encoding preset. The biggest difference between AVX2 enabled
and disabled was 35% (64-bit flac.exe, 24-bit WAV input file).
The smallest difference was 10% (32-bit flac.exe, 16-bit WAV input file).
> Disassembly of the object files (before and after) is here:
> This is with clang version 3.8.1 from Debian testing.
I forgot that all avx2 functions are inside "#ifdef FLAC__AVX2_SUPPORTED"
conditional, so they simply don't exist if FLAC__AVX2_SUPPORTED is not set.
Anyway, stream_encoder_intrin_avx2-after.txt shows that the code
contains AVX2 instructions such as vpabsd/vpaddd/vphaddd, so
this function was compiled properly.
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