[llvm-bugs] [Bug 27737] New: [SSE2] poor performance _mm_extract_epi8

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=27737

            Bug ID: 27737
           Summary: [SSE2] poor performance _mm_extract_epi8
           Product: clang
           Version: 3.8
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Headers
          Assignee: unassignedclangbugs at nondot.org
          Reporter: rozhuk.im at gmail.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

I have some code that heavy uses _mm_extract_epi8().
Then I build with clang 3.8 and -msse2 (without -msse4.1) then program work
very slow.

To build with GCC and clang 3.4, 3.6, 3.7 I use macro:

#ifndef _mm_extract_epi8 /* SSE4.1 required. */
#define _mm_extract_epi8(__xmm, __n)                    \
    ((_mm_extract_epi16(__xmm, ((__n) >> 1)) >> (8 * ((__n) & 1))) & 0xff)
#endif


Test results:

AMD Athlon(tm) 5350 APU with Radeon(tm) R3      (2050.04-MHz K8-class CPU)
GCC:        20391006000 (SSE4.1) /  20116413000 (SSE2)
clang 3.8:    22329895000 (SSE4.1) / 117304135000 (SSE2) !!!
clang 3.7:    22367008000 (SSE4.1) /  25542571000 (SSE2)
clang 3.6:    22306648000 (SSE4.1) /  25914115000 (SSE2)
clang 3.4:    23684031000 (SSE4.1) /  25914115000 (SSE2)

Intel(R) Core(TM)2 Duo CPU     E8400  @ 3.00GHz (2999.72-MHz K8-class CPU)
GCC:        12031595000 (SSE4.1) / 12011303000 (SSE2)
clang 3.8:    12431116000 (SSE4.1) / 73035466000 (SSE2) !!!
clang 3.7:    12458839000 (SSE4.1) / 13317058000 (SSE2)
clang 3.6:    12462181000 (SSE4.1) / 14119683000 (SSE2)
clang 3.4:    13555167000 (SSE4.1) / 13178893000 (SSE2)

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