[lld] r177562 - [ELF][Reader] Refactor how relocations are read. Improves performance.

[Michael J. Spencer]

Author: mspencer
Date: Wed Mar 20 14:25:47 2013
New Revision: 177562

URL: http://llvm.org/viewvc/llvm-project?rev=177562&view=rev
Log:
[ELF][Reader] Refactor how relocations are read. Improves performance.

This changes from reading each relocation individually for each section to just
storing the range of relocations. It also counts the relocations to preallocate
the _references array.

Modified:
    lld/trunk/lib/ReaderWriter/ELF/File.h

Modified: lld/trunk/lib/ReaderWriter/ELF/File.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/lib/ReaderWriter/ELF/File.h?rev=177562&r1=177561&r2=177562&view=diff
==============================================================================
--- lld/trunk/lib/ReaderWriter/ELF/File.h (original)
+++ lld/trunk/lib/ReaderWriter/ELF/File.h Wed Mar 20 14:25:47 2013
@@ -150,6 +150,8 @@ public:
     // the contents to the RelocationReferences map.
     llvm::object::section_iterator sit(_objFile->begin_sections());
     llvm::object::section_iterator sie(_objFile->end_sections());
+    // Record the number of relocs to guess at preallocating the buffer.
+    uint64_t totalRelocs = 0;
     for (; sit != sie; sit.increment(EC)) {
       if (EC)
         return;
@@ -194,10 +196,8 @@ public:
         auto rai(_objFile->beginELFRela(section));
         auto rae(_objFile->endELFRela(section));
 
-        auto &Ref = _relocationAddendRefences[sectionName];
-        for (; rai != rae; ++rai) {
-          Ref.push_back(&*rai);
-        }
+        _relocationAddendRefences[sectionName] = make_range(rai, rae);
+        totalRelocs += std::distance(rai, rae);
       }
 
       if (section->sh_type == llvm::ELF::SHT_REL) {
@@ -211,12 +211,11 @@ public:
         auto ri(_objFile->beginELFRel(section));
         auto re(_objFile->endELFRel(section));
 
-        auto &Ref = _relocationReferences[sectionName];
-        for (; ri != re; ++ri) {
-          Ref.push_back(&*ri);
-        }
+        _relocationReferences[sectionName] = make_range(ri, re);
+        totalRelocs += std::distance(ri, re);
       }
     }
+    _references.reserve(totalRelocs);
 
     // Divide the section that contains mergeable strings into tokens
     // TODO
@@ -573,25 +572,25 @@ private:
     auto rri = _relocationReferences.find(sectionName);
     if (rari != _relocationAddendRefences.end())
       for (auto &rai : rari->second) {
-        if (!((rai->r_offset >= symbol->st_value) &&
-              (rai->r_offset < symbol->st_value + content.size())))
+        if (!((rai.r_offset >= symbol->st_value) &&
+              (rai.r_offset < symbol->st_value + content.size())))
           continue;
         auto *ERef = new (_readerStorage)
-            ELFReference<ELFT>(rai, rai->r_offset - symbol->st_value, nullptr);
+            ELFReference<ELFT>(&rai, rai.r_offset - symbol->st_value, nullptr);
         _references.push_back(ERef);
       }
 
     // Add Rel references.
     if (rri != _relocationReferences.end())
       for (auto &ri : rri->second) {
-        if ((ri->r_offset >= symbol->st_value) &&
-            (ri->r_offset < symbol->st_value + content.size())) {
+        if ((ri.r_offset >= symbol->st_value) &&
+            (ri.r_offset < symbol->st_value + content.size())) {
           auto *ERef = new (_readerStorage)
-              ELFReference<ELFT>(ri, ri->r_offset - symbol->st_value, nullptr);
+              ELFReference<ELFT>(&ri, ri.r_offset - symbol->st_value, nullptr);
           // Read the addend from the section contents
           // TODO : We should move the way lld reads relocations totally from
           // ELFObjectFile
-          int32_t addend = *(content.data() + ri->r_offset - symbol->st_value);
+          int32_t addend = *(content.data() + ri.r_offset - symbol->st_value);
           ERef->setAddend(addend);
           _references.push_back(ERef);
         }
@@ -603,6 +602,7 @@ private:
               referenceStart, _references.size(), _references);
   }
 
+  llvm::BumpPtrAllocator _readerStorage;
   std::unique_ptr<llvm::object::ELFObjectFile<ELFT> > _objFile;
   atom_collection_vector<DefinedAtom> _definedAtoms;
   atom_collection_vector<UndefinedAtom> _undefinedAtoms;
@@ -614,14 +614,17 @@ private:
   /// relocations will also have a section named ".rel.text" or ".rela.text"
   /// which will hold the entries. -- .rel or .rela is prepended to create
   /// the SHT_REL(A) section name.
-  std::unordered_map<StringRef,
-                     std::vector<const Elf_Rela *> > _relocationAddendRefences;
+  std::unordered_map<
+      StringRef,
+      range<typename llvm::object::ELFObjectFile<ELFT>::Elf_Rela_Iter>>
+    _relocationAddendRefences;
   MergedSectionMapT _mergedSectionMap;
-  std::unordered_map<StringRef,
-                     std::vector<const Elf_Rel *> > _relocationReferences;
+  std::unordered_map<
+      StringRef,
+      range<typename llvm::object::ELFObjectFile<ELFT>::Elf_Rel_Iter>>
+    _relocationReferences;
   std::vector<ELFReference<ELFT> *> _references;
   llvm::DenseMap<const Elf_Sym *, Atom *> _symbolToAtomMapping;
-  llvm::BumpPtrAllocator _readerStorage;
   const ELFTargetInfo &_elfTargetInfo;
   MergeAtomsT _mergeAtoms;
 };