[lld] r316251 - Don't call buildSectionOrder multiple times.

[Shoaib Meenai via llvm-commits]

Rui had a talk on LLD at the developer meeting, and the talk included some
link time numbers. The Linux kernel was the only instance of gold being faster
than LLD, and a lot of people (including myself) were wondering why that was
the case. This is awesome :)

On 10/20/17, 5:05 PM, "llvm-commits on behalf of Rafael Espindola via llvm-commits" <llvm-commits-bounces at lists.llvm.org on behalf of llvm-commits at lists.llvm.org> wrote:

    Author: rafael
    Date: Fri Oct 20 17:05:01 2017
    New Revision: 316251
    
    URL: https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject-3Frev-3D316251-26view-3Drev&d=DwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=4IyeZA5wFDIztRZwT5Ikft6eluO180gbHODF81Mf3Ug&s=nNq0DR5WWlYGE3cjull_12CMiIvQooETqug4_X5eGLk&e=
    Log:
    Don't call buildSectionOrder multiple times.
    
    This takes linking the linux kernel from 1.52s to 0.58s.
    
    Modified:
        lld/trunk/ELF/InputSection.cpp
        lld/trunk/ELF/LinkerScript.cpp
        lld/trunk/ELF/LinkerScript.h
    
    Modified: lld/trunk/ELF/InputSection.cpp
    URL: https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_lld_trunk_ELF_InputSection.cpp-3Frev-3D316251-26r1-3D316250-26r2-3D316251-26view-3Ddiff&d=DwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=4IyeZA5wFDIztRZwT5Ikft6eluO180gbHODF81Mf3Ug&s=Behy9uothqGelaSOG4LvVOUM2TN8W9eggw9YF8Vj97o&e=
    ==============================================================================
    --- lld/trunk/ELF/InputSection.cpp (original)
    +++ lld/trunk/ELF/InputSection.cpp Fri Oct 20 17:05:01 2017
    @@ -46,6 +46,10 @@ std::string lld::toString(const InputSec
     }
     
     DenseMap<SectionBase *, int> elf::buildSectionOrder() {
    +  DenseMap<SectionBase *, int> SectionOrder;
    +  if (Config->SymbolOrderingFile.empty())
    +    return SectionOrder;
    +
       // Build a map from symbols to their priorities. Symbols that didn't
       // appear in the symbol ordering file have the lowest priority 0.
       // All explicitly mentioned symbols have negative (higher) priorities.
    @@ -55,7 +59,6 @@ DenseMap<SectionBase *, int> elf::buildS
         SymbolOrder.insert({S, Priority++});
     
       // Build a map from sections to their priorities.
    -  DenseMap<SectionBase *, int> SectionOrder;
       for (InputFile *File : ObjectFiles) {
         for (SymbolBody *Body : File->getSymbols()) {
           auto *D = dyn_cast<DefinedRegular>(Body);
    
    Modified: lld/trunk/ELF/LinkerScript.cpp
    URL: https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_lld_trunk_ELF_LinkerScript.cpp-3Frev-3D316251-26r1-3D316250-26r2-3D316251-26view-3Ddiff&d=DwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=4IyeZA5wFDIztRZwT5Ikft6eluO180gbHODF81Mf3Ug&s=Je_3iU9P1LF12KLZrW5An0DBWzvNjnYc1jc4UWEUv0g&e=
    ==============================================================================
    --- lld/trunk/ELF/LinkerScript.cpp (original)
    +++ lld/trunk/ELF/LinkerScript.cpp Fri Oct 20 17:05:01 2017
    @@ -274,9 +274,9 @@ static void sortInputSections(
     
     // Compute and remember which sections the InputSectionDescription matches.
     std::vector<InputSection *>
    -LinkerScript::computeInputSections(const InputSectionDescription *Cmd) {
    +LinkerScript::computeInputSections(const InputSectionDescription *Cmd,
    +                                   const DenseMap<SectionBase *, int> &Order) {
       std::vector<InputSection *> Ret;
    -  DenseMap<SectionBase *, int> Order = buildSectionOrder();
     
       // Collects all sections that satisfy constraints of Cmd.
       for (const SectionPattern &Pat : Cmd->SectionPatterns) {
    @@ -326,13 +326,13 @@ void LinkerScript::discard(ArrayRef<Inpu
       }
     }
     
    -std::vector<InputSection *>
    -LinkerScript::createInputSectionList(OutputSection &OutCmd) {
    +std::vector<InputSection *> LinkerScript::createInputSectionList(
    +    OutputSection &OutCmd, const DenseMap<SectionBase *, int> &Order) {
       std::vector<InputSection *> Ret;
     
       for (BaseCommand *Base : OutCmd.SectionCommands) {
         if (auto *Cmd = dyn_cast<InputSectionDescription>(Base)) {
    -      Cmd->Sections = computeInputSections(Cmd);
    +      Cmd->Sections = computeInputSections(Cmd, Order);
           Ret.insert(Ret.end(), Cmd->Sections.begin(), Cmd->Sections.end());
         }
       }
    @@ -359,6 +359,7 @@ void LinkerScript::processSectionCommand
       Ctx = make_unique<AddressState>();
       Ctx->OutSec = Aether;
     
    +  DenseMap<SectionBase *, int> Order = buildSectionOrder();
       // Add input sections to output sections.
       for (size_t I = 0; I < SectionCommands.size(); ++I) {
         // Handle symbol assignments outside of any output section.
    @@ -368,7 +369,7 @@ void LinkerScript::processSectionCommand
         }
     
         if (auto *Sec = dyn_cast<OutputSection>(SectionCommands[I])) {
    -      std::vector<InputSection *> V = createInputSectionList(*Sec);
    +      std::vector<InputSection *> V = createInputSectionList(*Sec, Order);
     
           // The output section name `/DISCARD/' is special.
           // Any input section assigned to it is discarded.
    
    Modified: lld/trunk/ELF/LinkerScript.h
    URL: https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_lld_trunk_ELF_LinkerScript.h-3Frev-3D316251-26r1-3D316250-26r2-3D316251-26view-3Ddiff&d=DwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=4IyeZA5wFDIztRZwT5Ikft6eluO180gbHODF81Mf3Ug&s=pbQ0x-JYey0QxqiIAbrRNWhQ6PJLgAuj9Mu8zFqXRco&e=
    ==============================================================================
    --- lld/trunk/ELF/LinkerScript.h (original)
    +++ lld/trunk/ELF/LinkerScript.h Fri Oct 20 17:05:01 2017
    @@ -205,9 +205,12 @@ class LinkerScript final {
       void setDot(Expr E, const Twine &Loc, bool InSec);
     
       std::vector<InputSection *>
    -  computeInputSections(const InputSectionDescription *);
    +  computeInputSections(const InputSectionDescription *,
    +                       const llvm::DenseMap<SectionBase *, int> &Order);
     
    -  std::vector<InputSection *> createInputSectionList(OutputSection &Cmd);
    +  std::vector<InputSection *>
    +  createInputSectionList(OutputSection &Cmd,
    +                         const llvm::DenseMap<SectionBase *, int> &Order);
     
       std::vector<size_t> getPhdrIndices(OutputSection *Sec);
     
    
    
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