more comment. optimize

Created using spr 1.3.5-bogner

Author: MaskRay

lld/MachO/BPSectionOrderer.cpp

@@ -118,32 +118,31 @@ struct BPOrdererMachO : lld::BPOrderer<BPOrdererMachO> {
 DenseMap<const InputSection *, int> lld::macho::runBalancedPartitioning(
     StringRef profilePath, bool forFunctionCompression, bool forDataCompression,
     bool compressionSortStartupFunctions, bool verbose) {
+  // Collect candidate sections and associated symbols.
   SmallVector<InputSection *> sections;
-  DenseMap<StringRef, DenseSet<unsigned>> symbolToSectionIdxs;
+  DenseMap<CachedHashStringRef, DenseSet<unsigned>> rootSymbolToSectionIdxs;
   for (const auto *file : inputFiles) {
     for (auto *sec : file->sections) {
       for (auto &subsec : sec->subsections) {
         auto *isec = subsec.isec;
         if (!isec || isec->data.empty())
           continue;
-        for (auto *sym : BPOrdererMachO::getSymbols(*isec))
-          symbolToSectionIdxs[sym->getName()].insert(sections.size());
+        size_t idx = sections.size();
         sections.emplace_back(isec);
+        for (auto *sym : BPOrdererMachO::getSymbols(*isec)) {
+          auto rootName = getRootSymbol(sym->getName());
+          rootSymbolToSectionIdxs[CachedHashStringRef(rootName)].insert(idx);
+          if (auto linkageName =
+                  BPOrdererMachO::getResolvedLinkageName(rootName))
+            rootSymbolToSectionIdxs[CachedHashStringRef(*linkageName)].insert(
+                idx);
+        }
       }
     }
   }
 
-  DenseMap<CachedHashStringRef, DenseSet<unsigned>> rootSymbolToSectionIdxs;
-  for (auto &[name, sectionIdxs] : symbolToSectionIdxs) {
-    auto rootName = getRootSymbol(name);
-    rootSymbolToSectionIdxs[CachedHashStringRef(rootName)].insert(
-        sectionIdxs.begin(), sectionIdxs.end());
-    if (auto linkageName = BPOrdererMachO::getResolvedLinkageName(rootName))
-      rootSymbolToSectionIdxs[CachedHashStringRef(*linkageName)].insert(
-          sectionIdxs.begin(), sectionIdxs.end());
-  }
-  return BPOrdererMachO::reorderSections(
-      profilePath, forFunctionCompression, forDataCompression,
-      compressionSortStartupFunctions, verbose, sections,
-      rootSymbolToSectionIdxs);
+  return BPOrdererMachO::computeOrder(profilePath, forFunctionCompression,
+                                      forDataCompression,
+                                      compressionSortStartupFunctions, verbose,
+                                      sections, rootSymbolToSectionIdxs);
 }

lld/include/lld/Common/BPSectionOrdererBase.inc

@@ -48,13 +48,20 @@ template <class D> struct BPOrderer {
   using Section = typename BPOrdererTraits<D>::Section;
   using Symbol = typename BPOrdererTraits<D>::Symbol;
 
-  // Reorder sections using balanced partitioning algorithm based on profile.
+  // Compute a section order using the Balanced Partitioning algorithm.
+  //
+  // * for*Compresion: Improve Lempel-Ziv compression by grouping
+  //   similar sections together.
+  // * profilePath: Utilize a temporal profile file to reduce page faults during
+  //   program startup.
+  // * compressionSortStartupFunctions: if profilePath is specified, allocate
+  //   extra utility vertices to prioritize nearby function similarity.
   static auto
-  reorderSections(llvm::StringRef profilePath, bool forFunctionCompression,
-                  bool forDataCompression, bool compressionSortStartupFunctions,
-                  bool verbose, llvm::ArrayRef<Section *> sections,
-                  const DenseMap<CachedHashStringRef, DenseSet<unsigned>>
-                      &rootSymbolToSectionIdxs)
+  computeOrder(llvm::StringRef profilePath, bool forFunctionCompression,
+               bool forDataCompression, bool compressionSortStartupFunctions,
+               bool verbose, llvm::ArrayRef<Section *> sections,
+               const DenseMap<CachedHashStringRef, DenseSet<unsigned>>
+                   &rootSymbolToSectionIdxs)
       -> llvm::DenseMap<const Section *, int>;
 };
 } // namespace lld
@@ -145,7 +152,7 @@ inline StringRef getRootSymbol(StringRef name) {
 }
 
 template <class D>
-auto BPOrderer<D>::reorderSections(
+auto BPOrderer<D>::computeOrder(
     StringRef profilePath, bool forFunctionCompression, bool forDataCompression,
     bool compressionSortStartupFunctions, bool verbose,
     ArrayRef<Section *> sections,