[llvm] r268698 - Make StringTableBuilder to cache hash values.

[Rafael Espíndola via llvm-commits]

It is amusing how useful this simple template is. How about we add it
to the programmers manual?

Cheers,
Rafael


On 5 May 2016 at 20:51, Rui Ueyama via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: ruiu
> Date: Thu May  5 19:51:58 2016
> New Revision: 268698
>
> URL: http://llvm.org/viewvc/llvm-project?rev=268698&view=rev
> Log:
> Make StringTableBuilder to cache hash values.
>
> This change seems to speed up LLD a bit if it has a lot of mergeable
> sections. The number is below. It's not too bad for a small patch.
>
> Time to link Clang (debug build):
>
> w/o patch 6.3696 seconds
> w/patch   6.2746 seconds (-1.5%)
>
> Differential Revision: http://reviews.llvm.org/D19933
>
> Modified:
>     llvm/trunk/include/llvm/MC/StringTableBuilder.h
>     llvm/trunk/lib/MC/StringTableBuilder.cpp
>
> Modified: llvm/trunk/include/llvm/MC/StringTableBuilder.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/MC/StringTableBuilder.h?rev=268698&r1=268697&r2=268698&view=diff
> ==============================================================================
> --- llvm/trunk/include/llvm/MC/StringTableBuilder.h (original)
> +++ llvm/trunk/include/llvm/MC/StringTableBuilder.h Thu May  5 19:51:58 2016
> @@ -23,7 +23,7 @@ public:
>
>  private:
>    SmallString<256> StringTable;
> -  DenseMap<StringRef, size_t> StringIndexMap;
> +  DenseMap<CachedHash<StringRef>, size_t> StringIndexMap;
>    size_t Size = 0;
>    Kind K;
>    unsigned Alignment;
> @@ -57,7 +57,10 @@ public:
>    /// after the table is finalized.
>    size_t getOffset(StringRef S) const;
>
> -  const DenseMap<StringRef, size_t> &getMap() const { return StringIndexMap; }
> +  const DenseMap<CachedHash<StringRef>, size_t> &getMap() const {
> +    return StringIndexMap;
> +  }
> +
>    size_t getSize() const { return Size; }
>    void clear();
>
>
> Modified: llvm/trunk/lib/MC/StringTableBuilder.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/MC/StringTableBuilder.cpp?rev=268698&r1=268697&r2=268698&view=diff
> ==============================================================================
> --- llvm/trunk/lib/MC/StringTableBuilder.cpp (original)
> +++ llvm/trunk/lib/MC/StringTableBuilder.cpp Thu May  5 19:51:58 2016
> @@ -34,11 +34,11 @@ StringTableBuilder::StringTableBuilder(K
>    }
>  }
>
> -typedef std::pair<StringRef, size_t> StringPair;
> +typedef std::pair<CachedHash<StringRef>, size_t> StringPair;
>
>  // Returns the character at Pos from end of a string.
>  static int charTailAt(StringPair *P, size_t Pos) {
> -  StringRef S = P->first;
> +  StringRef S = P->first.Val;
>    if (Pos >= S.size())
>      return -1;
>    return (unsigned char)S[S.size() - Pos - 1];
> @@ -86,7 +86,7 @@ void StringTableBuilder::finalizeInOrder
>  }
>
>  void StringTableBuilder::finalizeStringTable(bool Optimize) {
> -  typedef std::pair<StringRef, size_t> StringOffsetPair;
> +  typedef std::pair<CachedHash<StringRef>, size_t> StringOffsetPair;
>    std::vector<StringOffsetPair *> Strings;
>    Strings.reserve(StringIndexMap.size());
>    for (StringOffsetPair &P : StringIndexMap)
> @@ -121,7 +121,7 @@ void StringTableBuilder::finalizeStringT
>
>    StringRef Previous;
>    for (StringOffsetPair *P : Strings) {
> -    StringRef S = P->first;
> +    StringRef S = P->first.Val;
>      if (K == WinCOFF)
>        assert(S.size() > COFF::NameSize && "Short string in COFF string table!");
>
>
>
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