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llvm-vpopcount

Evaluation of LLVM x86 vector population count implementation.

Currently, scalar+ctpop and parallelbitmath are used for population count on vector types. The idea is to replace them by sselookup wherever it's profitable.

v4i32-avx

  • sselookup (v4i32): 1.10211
  • scalar + ctpop (v4i32): 0.907016
  • parallelbitmath (v4i32): 1.14124

v8i32-avx

  • sselookup (v8i32): 1.97514
  • scalar + ctpop (v8i32): 2.37118

v8i32-avx2
Multiple runs for both implementations below presented similar results, but parallelbitmath performs better on most of them.

  • sselookup (v8i32): 1.17823
  • parallelbitmath (v8i32): 1.15288

v2i64-avx

  • scalar + ctpop (v2i64): 0.589292
  • sselookup (v2i64): 0.865797
  • parallelbitmath (v2i64): 1.31027

v4i64-avx

  • scalar + ctpop (v4i64): 0.903523
  • sselookup (v4i64): 1.11988

v4i64-avx2

  • scalar + ctpop (v4i64): 0.895486
  • sselookup (v4i64): 0.677801
  • parallelbitmath (v4i64): 1.02711

v16i8-avx

  • scalar + ctpop (v16i8): 4.1569
  • sselookup (v16i8): 0.508693

v32i8-avx

  • scalar + ctpop (v32i8): 8.32336
  • sselookup (v32i8): 0.961657

v32i8-avx2

  • scalar + ctpop (v32i8): 8.79509
  • sselookup (v32i8): 0.487716

v8i16-avx

  • scalar + ctpop (v8i16): 1.86908
  • sselookup (v8i16): 0.755885

v16i16-avx

  • scalar + ctpop (v16i16): 4.08575
  • sselookup (v16i16): 1.32838

v16i16-avx2

  • scalar + ctpop (v16i16): 4.19101
  • sselookup (v16i16): 1.18095

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Evaluation of LLVM vector popcount implementation

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