[PATCH] D112175: [NFC] Add llvm::StaticVector ADT

[James Player via Phabricator via llvm-commits]

jplayer-nv added a comment.

Just to give a concrete example of what I believe to be the benefit behind `StaticVector`, I ran this contrived test pitting `SmallVector<uint64_t,N>` vs `StaticVector<uint64_t,N>` (with a few tweaks to ensure the `push_back` param is passsed by value like in `SmallVector`):

  TYPED_TEST(StaticVsSmall, TimedStaticVector) {
    const size_t N = this->NumBuiltinElts(this->TheStaticVector);
    for (int I = 0; I < OutterLimit; ++I) {
      this->TheStaticVector.clear();
      for (int J = 0; J < N; ++J) {
        this->TheStaticVector.push_back(I + J);
      }
    }
  }
  
  TYPED_TEST(StaticVsSmall, TimedSmallVector) {
    const size_t N = this->NumBuiltinElts(this->TheSmallVector);
    for (int I = 0; I < OutterLimit; ++I) {
      this->TheSmallVector.clear();
      for (int J = 0; J < N; ++J) {
        this->TheSmallVector.push_back(I + J);
      }
    }
  }

My local results are:

  [ RUN      ] StaticVsSmall/0.TimedStaticVector
  [       OK ] StaticVsSmall/0.TimedStaticVector (371 ms)
  [ RUN      ] StaticVsSmall/0.TimedSmallVector
  [       OK ] StaticVsSmall/0.TimedSmallVector (596 ms)

Which demonstrates that simple insertions are significantly faster (almost 38%) with the `StaticVector` compared to a `SmallVector` which stays within its small buffer limit.

I would think it interesting to speed up `SmallSet` insertions by retargeting the small storage to a `StaticVector`.


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https://reviews.llvm.org/D112175