[lld] r266357 - Hash symbol names only once per global SymbolBody.

[Rafael Espindola via llvm-commits]

Author: rafael
Date: Thu Apr 14 14:17:16 2016
New Revision: 266357

URL: http://llvm.org/viewvc/llvm-project?rev=266357&view=rev
Log:
Hash symbol names only once per global SymbolBody.

The DenseMap doesn't store hash results. This means that when it is
resized it has to recompute them.

This patch is a small hack that wraps the StringRef in a struct that
remembers the hash value. That way we can be sure it is only hashed
once.

Modified:
    lld/trunk/ELF/MarkLive.cpp
    lld/trunk/ELF/SymbolTable.h

Modified: lld/trunk/ELF/MarkLive.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/MarkLive.cpp?rev=266357&r1=266356&r2=266357&view=diff
==============================================================================
--- lld/trunk/ELF/MarkLive.cpp (original)
+++ lld/trunk/ELF/MarkLive.cpp Thu Apr 14 14:17:16 2016
@@ -113,7 +113,7 @@ template <class ELFT> void elf::markLive
   // Preserve externally-visible symbols if the symbols defined by this
   // file can interrupt other ELF file's symbols at runtime.
   if (Config->Shared || Config->ExportDynamic) {
-    for (const std::pair<StringRef, Symbol *> &P : Symtab->getSymbols()) {
+    for (const std::pair<SymName, Symbol *> &P : Symtab->getSymbols()) {
       SymbolBody *B = P.second->Body;
       if (B->getVisibility() == STV_DEFAULT)
         MarkSymbol(B);

Modified: lld/trunk/ELF/SymbolTable.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/SymbolTable.h?rev=266357&r1=266356&r2=266357&view=diff
==============================================================================
--- lld/trunk/ELF/SymbolTable.h (original)
+++ lld/trunk/ELF/SymbolTable.h Thu Apr 14 14:17:16 2016
@@ -20,6 +20,37 @@ class Lazy;
 template <class ELFT> class OutputSectionBase;
 struct Symbol;
 
+struct SymName {
+  SymName(StringRef Name) : Name(Name) {
+    Hash = llvm::DenseMapInfo<StringRef>::getHashValue(Name);
+  }
+  SymName(StringRef Name, unsigned Hash) : Name(Name), Hash(Hash) {}
+  StringRef Name;
+  unsigned Hash;
+};
+}
+}
+
+namespace llvm {
+template <> struct DenseMapInfo<lld::elf::SymName> {
+  static lld::elf::SymName getEmptyKey() {
+    StringRef N = DenseMapInfo<StringRef>::getEmptyKey();
+    return {N, 0};
+  }
+  static lld::elf::SymName getTombstoneKey() {
+    StringRef N = DenseMapInfo<StringRef>::getTombstoneKey();
+    return {N, 0};
+  }
+  static unsigned getHashValue(lld::elf::SymName Name) { return Name.Hash; }
+  static bool isEqual(lld::elf::SymName A, lld::elf::SymName B) {
+    return A.Name == B.Name;
+  }
+};
+}
+
+namespace lld {
+namespace elf {
+
 // SymbolTable is a bucket of all known symbols, including defined,
 // undefined, or lazy symbols (the last one is symbols in archive
 // files whose archive members are not yet loaded).
@@ -38,7 +69,7 @@ public:
   void addFile(std::unique_ptr<InputFile> File);
   void addCombinedLtoObject();
 
-  const llvm::MapVector<StringRef, Symbol *> &getSymbols() const {
+  const llvm::MapVector<SymName, Symbol *> &getSymbols() const {
     return Symtab;
   }
 
@@ -79,7 +110,7 @@ private:
   // a bit inefficient.
   // FIXME: Experiment with passing in a custom hashing or sorting the symbols
   // once symbol resolution is finished.
-  llvm::MapVector<StringRef, Symbol *> Symtab;
+  llvm::MapVector<SymName, Symbol *> Symtab;
   llvm::BumpPtrAllocator Alloc;
 
   // Comdat groups define "link once" sections. If two comdat groups have the