[PATCH] D27648: COFF: Use a bit in SymbolBody to track which symbols are written to the symbol table.

[Peter Collingbourne via Phabricator via llvm-commits]

pcc created this revision.
pcc added a reviewer: ruiu.
pcc added a subscriber: llvm-commits.

Using a set here caused us to take about 1 second longer to write the symbol
table when linking chrome_child.dll. With this I consistently get better
performance on Windows with the new symbol table.

Before r289280 and with r289183 reverted (median of 5 runs): 17.65s
After this change: 17.33s

On Linux things look even better:

Before: 10.700480444s
After: 5.735681610s


https://reviews.llvm.org/D27648

Files:
  lld/COFF/Symbols.h
  lld/COFF/Writer.cpp


Index: lld/COFF/Writer.cpp
===================================================================
--- lld/COFF/Writer.cpp
+++ lld/COFF/Writer.cpp
@@ -533,13 +533,14 @@
     Sec->setStringTableOff(addEntryToStringTable(Name));
   }
 
-  std::set<SymbolBody *> SeenSymbols;
   for (lld::coff::ObjectFile *File : Symtab->ObjectFiles)
     for (SymbolBody *B : File->getSymbols())
       if (auto *D = dyn_cast<Defined>(B))
-        if (SeenSymbols.insert(D).second)
+        if (!D->WrittenToSymtab) {
+          D->WrittenToSymtab = true;
           if (Optional<coff_symbol16> Sym = createSymbol(D))
             OutputSymtab.push_back(*Sym);
+        }
 
   OutputSection *LastSection = OutputSections.back();
   // We position the symbol table to be adjacent to the end of the last section.
Index: lld/COFF/Symbols.h
===================================================================
--- lld/COFF/Symbols.h
+++ lld/COFF/Symbols.h
@@ -80,7 +80,7 @@
   friend SymbolTable;
   explicit SymbolBody(Kind K, StringRef N = "")
       : SymbolKind(K), IsExternal(true), IsCOMDAT(false),
-        IsReplaceable(false), Name(N) {}
+        IsReplaceable(false), WrittenToSymtab(false), Name(N) {}
 
   const unsigned SymbolKind : 8;
   unsigned IsExternal : 1;
@@ -91,6 +91,11 @@
   // This bit is used by the \c DefinedBitcode subclass.
   unsigned IsReplaceable : 1;
 
+public:
+  // This bit is used by Writer::createSymbolAndStringTable().
+  unsigned WrittenToSymtab : 1;
+
+protected:
   StringRef Name;
 };
 


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