[lld] r289408 - COFF: Use a bit in SymbolBody to track which symbols are written to the symbol table.

[Peter Collingbourne via llvm-commits]

Author: pcc
Date: Sun Dec 11 16:15:20 2016
New Revision: 289408

URL: http://llvm.org/viewvc/llvm-project?rev=289408&view=rev
Log:
COFF: Use a bit in SymbolBody to track which symbols are written to the symbol table.

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

Differential Revision: https://reviews.llvm.org/D27648

Modified:
    lld/trunk/COFF/Symbols.h
    lld/trunk/COFF/Writer.cpp

Modified: lld/trunk/COFF/Symbols.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/Symbols.h?rev=289408&r1=289407&r2=289408&view=diff
==============================================================================
--- lld/trunk/COFF/Symbols.h (original)
+++ lld/trunk/COFF/Symbols.h Sun Dec 11 16:15:20 2016
@@ -80,7 +80,7 @@ protected:
   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 @@ protected:
   // 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;
 };
 

Modified: lld/trunk/COFF/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/Writer.cpp?rev=289408&r1=289407&r2=289408&view=diff
==============================================================================
--- lld/trunk/COFF/Writer.cpp (original)
+++ lld/trunk/COFF/Writer.cpp Sun Dec 11 16:15:20 2016
@@ -533,13 +533,14 @@ void Writer::createSymbolAndStringTable(
     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.