[lld] r270572 - Do not start over relocation search from beginning.

[Rafael Espíndola via llvm-commits]

Thanks!

On 24 May 2016 at 11:40, Rui Ueyama via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: ruiu
> Date: Tue May 24 10:40:46 2016
> New Revision: 270572
>
> URL: http://llvm.org/viewvc/llvm-project?rev=270572&view=rev
> Log:
> Do not start over relocation search from beginning.
>
> This patch addresses a post-commit review for r270325. r270325
> introduced getReloc function that searches a relocation for a
> given range. It always started searching from beginning of relocation
> vector, so it was slower than before. Previously, we used to use
> the fact that the relocations are sorted. This patch restore it.
>
> Modified:
>     lld/trunk/ELF/OutputSections.cpp
>     lld/trunk/ELF/OutputSections.h
>
> Modified: lld/trunk/ELF/OutputSections.cpp
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/OutputSections.cpp?rev=270572&r1=270571&r2=270572&view=diff
> ==============================================================================
> --- lld/trunk/ELF/OutputSections.cpp (original)
> +++ lld/trunk/ELF/OutputSections.cpp Tue May 24 10:40:46 2016
> @@ -920,14 +920,21 @@ void EhOutputSection<ELFT>::forEachInput
>  // Returns the first relocation that points to a region
>  // between Begin and Begin+Size.
>  template <class IntTy, class RelTy>
> -static const RelTy *getReloc(IntTy Begin, IntTy Size, ArrayRef<RelTy> Rels) {
> -  size_t I = 0;
> -  size_t E = Rels.size();
> -  while (I != E && Rels[I].r_offset < Begin)
> -    ++I;
> -  if (I == E || Begin + Size <= Rels[I].r_offset)
> +static const RelTy *getReloc(IntTy Begin, IntTy Size, ArrayRef<RelTy> &Rels) {
> +  for (auto I = Rels.begin(), E = Rels.end(); I != E; ++I) {
> +    if (I->r_offset < Begin)
> +      continue;
> +
> +    // Truncate Rels for fast access. That means we expect that the
> +    // relocations are sorted and we are looking up symbols in
> +    // sequential order. It is naturally satisfied for .eh_frame.
> +    Rels = Rels.slice(I - Rels.begin());
> +    if (I->r_offset < Begin + Size)
> +      return I;
>      return nullptr;
> -  return &Rels[I];
> +  }
> +  Rels = ArrayRef<RelTy>();
> +  return nullptr;
>  }
>
>  // Search for an existing CIE record or create a new one.
> @@ -937,7 +944,7 @@ template <class ELFT>
>  template <class RelTy>
>  CieRecord *EhOutputSection<ELFT>::addCie(SectionPiece &Piece,
>                                           EhInputSection<ELFT> *Sec,
> -                                         ArrayRef<RelTy> Rels) {
> +                                         ArrayRef<RelTy> &Rels) {
>    const endianness E = ELFT::TargetEndianness;
>    if (read32<E>(Piece.Data.data() + 4) != 0)
>      fatal("CIE expected at beginning of .eh_frame: " + Sec->getSectionName());
> @@ -971,7 +978,7 @@ template <class ELFT>
>  template <class RelTy>
>  bool EhOutputSection<ELFT>::isFdeLive(SectionPiece &Piece,
>                                        EhInputSection<ELFT> *Sec,
> -                                      ArrayRef<RelTy> Rels) {
> +                                      ArrayRef<RelTy> &Rels) {
>    const RelTy *Rel = getReloc(Piece.InputOff, Piece.size(), Rels);
>    if (!Rel)
>      fatal("FDE doesn't reference another section");
>
> Modified: lld/trunk/ELF/OutputSections.h
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/OutputSections.h?rev=270572&r1=270571&r2=270572&view=diff
> ==============================================================================
> --- lld/trunk/ELF/OutputSections.h (original)
> +++ lld/trunk/ELF/OutputSections.h Tue May 24 10:40:46 2016
> @@ -357,11 +357,11 @@ private:
>
>    template <class RelTy>
>    CieRecord *addCie(SectionPiece &Piece, EhInputSection<ELFT> *Sec,
> -                    ArrayRef<RelTy> Rels);
> +                    ArrayRef<RelTy> &Rels);
>
>    template <class RelTy>
>    bool isFdeLive(SectionPiece &Piece, EhInputSection<ELFT> *Sec,
> -                 ArrayRef<RelTy> Rels);
> +                 ArrayRef<RelTy> &Rels);
>
>    uintX_t getFdePc(uint8_t *Buf, size_t Off, uint8_t Enc);
>
>
>
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