[lld] r329106 - ELF: Use a vector of pairs to sort sections ordered using --symbol-ordering-file.

[Rafael Avila de Espindola via llvm-commits]

Thanks!

Peter Collingbourne via llvm-commits <llvm-commits at lists.llvm.org>
writes:

> Author: pcc
> Date: Tue Apr  3 12:45:10 2018
> New Revision: 329106
>
> URL: http://llvm.org/viewvc/llvm-project?rev=329106&view=rev
> Log:
> ELF: Use a vector of pairs to sort sections ordered using --symbol-ordering-file.
>
> This improved performance by 0.5-1% linking Chromium for Android.
>
> Differential Revision: https://reviews.llvm.org/D45222
>
> Modified:
>     lld/trunk/ELF/Writer.cpp
>
> Modified: lld/trunk/ELF/Writer.cpp
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=329106&r1=329105&r2=329106&view=diff
> ==============================================================================
> --- lld/trunk/ELF/Writer.cpp (original)
> +++ lld/trunk/ELF/Writer.cpp Tue Apr  3 12:45:10 2018
> @@ -1092,21 +1092,23 @@ static void
>  sortISDBySectionOrder(InputSectionDescription *ISD,
>                        const DenseMap<const InputSectionBase *, int> &Order) {
>    std::vector<InputSection *> UnorderedSections;
> -  std::vector<InputSection *> OrderedSections;
> +  std::vector<std::pair<InputSection *, int>> OrderedSections;
>    uint64_t UnorderedSize = 0;
>  
>    for (InputSection *IS : ISD->Sections) {
> -    if (!Order.count(IS)) {
> +    auto I = Order.find(IS);
> +    if (I == Order.end()) {
>        UnorderedSections.push_back(IS);
>        UnorderedSize += IS->getSize();
>        continue;
>      }
> -    OrderedSections.push_back(IS);
> +    OrderedSections.push_back({IS, I->second});
>    }
> -  std::sort(OrderedSections.begin(), OrderedSections.end(),
> -            [&](InputSection *A, InputSection *B) {
> -              return Order.lookup(A) < Order.lookup(B);
> -            });
> +  std::sort(
> +      OrderedSections.begin(), OrderedSections.end(),
> +      [&](std::pair<InputSection *, int> A, std::pair<InputSection *, int> B) {
> +        return A.second < B.second;
> +      });
>  
>    // Find an insertion point for the ordered section list in the unordered
>    // section list. On targets with limited-range branches, this is the mid-point
> @@ -1147,10 +1149,12 @@ sortISDBySectionOrder(InputSectionDescri
>  
>    std::copy(UnorderedSections.begin(),
>              UnorderedSections.begin() + UnorderedInsPt, ISD->Sections.begin());
> -  std::copy(OrderedSections.begin(), OrderedSections.end(),
> -            ISD->Sections.begin() + UnorderedInsPt);
> +  std::vector<InputSection *>::iterator SectionsPos =
> +      ISD->Sections.begin() + UnorderedInsPt;
> +  for (std::pair<InputSection *, int> P : OrderedSections)
> +    *SectionsPos++ = P.first;
>    std::copy(UnorderedSections.begin() + UnorderedInsPt, UnorderedSections.end(),
> -            ISD->Sections.begin() + UnorderedInsPt + OrderedSections.size());
> +            SectionsPos);
>  }
>  
>  static void sortSection(OutputSection *Sec,
>
>
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