[lld] r309652 - Binary search to find a relocation.

[Rafael Avila de Espindola via llvm-commits]

This is awesome. It takes a link of clang with gdb index from about 21
seconds to 13.5 seconds for me!

Cheers,
Rafael

Rui Ueyama via llvm-commits <llvm-commits at lists.llvm.org> writes:

> Author: ruiu
> Date: Mon Jul 31 21:11:03 2017
> New Revision: 309652
>
> URL: http://llvm.org/viewvc/llvm-project?rev=309652&view=rev
> Log:
> Binary search to find a relocation.
>
> This change makes -gdb-index 40% faster. My test case is self-linking lld.
>
> Differential Revision: https://reviews.llvm.org/D36079
>
> Modified:
>     lld/trunk/ELF/GdbIndex.cpp
>
> Modified: lld/trunk/ELF/GdbIndex.cpp
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/GdbIndex.cpp?rev=309652&r1=309651&r2=309652&view=diff
> ==============================================================================
> --- lld/trunk/ELF/GdbIndex.cpp (original)
> +++ lld/trunk/ELF/GdbIndex.cpp Mon Jul 31 21:11:03 2017
> @@ -79,11 +79,13 @@ template <class RelTy>
>  Optional<RelocAddrEntry>
>  LLDDwarfObj<ELFT>::findAux(const InputSectionBase &Sec, uint64_t Pos,
>                             ArrayRef<RelTy> Rels) const {
> -  auto I = llvm::find_if(Rels,
> -                         [=](const RelTy &Rel) { return Rel.r_offset == Pos; });
> -  if (I == Rels.end())
> +  auto It = std::lower_bound(
> +      Rels.begin(), Rels.end(), Pos,
> +      [](const RelTy &A, uint64_t B) { return A.r_offset < B; });
> +  if (It == Rels.end() || It->r_offset != Pos)
>      return None;
> -  const RelTy &Rel = *I;
> +  const RelTy &Rel = *It;
> +
>    const ObjFile<ELFT> *File = Sec.getFile<ELFT>();
>    uint32_t SymIndex = Rel.getSymbol(Config->IsMips64EL);
>    const typename ELFT::Sym &Sym = File->getELFSymbols()[SymIndex];
>
>
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