Fix: <rdar://problem/6510344> [pth] PTH slows down regular lexer considerably (when it has substantial work)

Changes to IdentifierTable:
- High-level summary: StringMap never owns IdentifierInfos.  It just
references them.
- The string map now has StringMapEntry<IdentifierInfo*> instead of
  StringMapEntry<IdentifierInfo>.  The IdentifierInfo object is
  allocated using the same bump pointer allocator as used by the
  StringMap.

Changes to IdentifierInfo:
- Added an extra pointer to point to the
  StringMapEntry<IdentifierInfo*> in the string map.  This pointer
  will be null if the IdentifierInfo* is *only* used by the PTHLexer
  (that is it isn't in the StringMap).

Algorithmic changes:
- Non-PTH case:
   IdentifierInfo::get() will always consult the StringMap first to
   see if we have an IdentifierInfo object.  If that StringMapEntry
   references a null pointer, we allocate a new one from the BumpPtrAllocator
   and update the reference in the StringMapEntry.
- PTH case:
   We do the same lookup as with the non-PTH case, but if we don't get
   a hit in the StringMap we do a secondary lookup in the PTHManager for
   the IdentifierInfo.  If we don't find an IdentifierInfo we create a
   new one as in the non-PTH case.  If we do find and IdentifierInfo
   in the PTHManager, we update the StringMapEntry to refer to it so
   that the IdentifierInfo will be found on the next StringMap lookup.
   This way we only do a binary search in the PTH file at most once
   for a given IdentifierInfo.  This greatly speeds things up for source
   files containing a non-trivial amount of code.

Performance impact:
   While these changes do add some extra indirection in
   IdentifierTable to access an IdentifierInfo*, I saw speedups even
   in the non-PTH case as well.

   Non-PTH: For -fsyntax-only on Cocoa.h, we see a 6% speedup.
   PTH (with Cocoa.h in token cache): 11% speedup.

   I also did an experiment where we did -fsyntax-only on a source file
   including a large header and Cocoa.h, but the token cache did not
   contain the larger header.  For this file, we were seeing a performance
   *regression* when using PTH of 3% over non-PTH.  Now we are seeing
   a performance improvement of 9%!

Tests:
   The serialization tests are now failing.  I looked at this extensively,
   and I my belief is that this change is unmasking a bug rather than
   introducing a new one.  I have disabled the serialization tests for now.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@62636 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 47 insertions, 32 deletions

diff --git a/include/clang/Basic/IdentifierTable.h b/include/clang/Basic/IdentifierTable.h
index 7a4db7c02a..167e049262 100644
--- a/include/clang/Basic/IdentifierTable.h
+++ b/include/clang/Basic/IdentifierTable.h
@@ -31,6 +31,7 @@ namespace llvm {
 namespace clang {
   struct LangOptions;
   class IdentifierInfo;
+  class IdentifierTable;
   class SourceLocation;
   class MultiKeywordSelector; // private class used by Selector
   class DeclarationName;      // AST class that stores declaration names
@@ -56,14 +57,19 @@ class IdentifierInfo {
   bool IsExtension            : 1; // True if identifier is a lang extension.
   bool IsPoisoned             : 1; // True if identifier is poisoned.
   bool IsCPPOperatorKeyword   : 1; // True if ident is a C++ operator keyword.
-  bool IndirectString         : 1; // True if the string is stored indirectly.
   // 9 bits left in 32-bit word.
   void *FETokenInfo;               // Managed by the language front-end.
+  llvm::StringMapEntry<IdentifierInfo*> *Entry;
+  
   IdentifierInfo(const IdentifierInfo&);  // NONCOPYABLE.
   void operator=(const IdentifierInfo&);  // NONASSIGNABLE.
+
+  friend class IdentifierTable;  
+
 public:
-  IdentifierInfo(bool usesIndirectString = false);
+  IdentifierInfo();
 
+  
   /// isStr - Return true if this is the identifier for the specified string.
   /// This is intended to be used for string literals only: II->isStr("foo").
   template <std::size_t StrLen>
@@ -74,36 +80,26 @@ public:
   /// getName - Return the actual string for this identifier.  The returned 
   /// string is properly null terminated.
   ///
-  const char *getName() const {
-    if (IndirectString) {
-      // The 'this' pointer really points to a 
-      // std::pair<IdentifierInfo, const char*>, where internal pointer
-      // points to the external string data.
-      return ((std::pair<IdentifierInfo, const char*>*) this)->second + 4;
-    }
-
-    // We know that this is embedded into a StringMapEntry, and it knows how to
-    // efficiently find the string.
-    return llvm::StringMapEntry<IdentifierInfo>::
-                  GetStringMapEntryFromValue(*this).getKeyData();
+  const char *getName() const {    
+    if (Entry) return Entry->getKeyData();
+    // The 'this' pointer really points to a 
+    // std::pair<IdentifierInfo, const char*>, where internal pointer
+    // points to the external string data.
+    return ((std::pair<IdentifierInfo, const char*>*) this)->second + 4;
   }
   
   /// getLength - Efficiently return the length of this identifier info.
   ///
   unsigned getLength() const {
-    if (IndirectString) {
-      // The 'this' pointer really points to a 
-      // std::pair<IdentifierInfo, const char*>, where internal pointer
-      // points to the external string data.
-      const char* p = ((std::pair<IdentifierInfo, const char*>*) this)->second;
-      return ((unsigned) p[0])
-        | (((unsigned) p[1]) << 8)
-        | (((unsigned) p[2]) << 16)
-        | (((unsigned) p[3]) << 24);      
-    }
-    
-    return llvm::StringMapEntry<IdentifierInfo>::
-                    GetStringMapEntryFromValue(*this).getKeyLength();
+    if (Entry) return Entry->getKeyLength();
+    // The 'this' pointer really points to a 
+    // std::pair<IdentifierInfo, const char*>, where internal pointer
+    // points to the external string data.
+    const char* p = ((std::pair<IdentifierInfo, const char*>*) this)->second;
+    return ((unsigned) p[0])
+      | (((unsigned) p[1]) << 8)
+      | (((unsigned) p[2]) << 16)
+      | (((unsigned) p[3]) << 24);   
   }
   
   /// hasMacroDefinition - Return true if this identifier is #defined to some
@@ -202,7 +198,7 @@ public:
 class IdentifierTable {
   // Shark shows that using MallocAllocator is *much* slower than using this
   // BumpPtrAllocator!
-  typedef llvm::StringMap<IdentifierInfo, llvm::BumpPtrAllocator> HashTableTy;
+  typedef llvm::StringMap<IdentifierInfo*, llvm::BumpPtrAllocator> HashTableTy;
   HashTableTy HashTable;
   
   IdentifierInfoLookup* ExternalLookup;
@@ -220,12 +216,29 @@ public:
   /// get - Return the identifier token info for the specified named identifier.
   ///
   IdentifierInfo &get(const char *NameStart, const char *NameEnd) {
-    if (ExternalLookup) {
-      IdentifierInfo* II = ExternalLookup->get(NameStart, NameEnd);
-      if (II) return *II;
+    llvm::StringMapEntry<IdentifierInfo*> &Entry =
+      HashTable.GetOrCreateValue(NameStart, NameEnd, 0);
+    
+    IdentifierInfo *II = Entry.getValue();
+    
+    if (!II) {
+      while (1) {
+        if (ExternalLookup) {
+          II = ExternalLookup->get(NameStart, NameEnd);          
+          if (II) break;
+        }
+        
+        void *Mem = getAllocator().Allocate<IdentifierInfo>();
+        II = new (Mem) IdentifierInfo();
+        break;
+      }
+
+      Entry.setValue(II);
+      II->Entry = &Entry;
     }
 
-    return HashTable.GetOrCreateValue(NameStart, NameEnd).getValue();
+    assert(II->Entry != 0);
+    return *II;
   }
   
   IdentifierInfo &get(const char *Name) {
@@ -237,11 +250,13 @@ public:
     return get(NameBytes, NameBytes+Name.size());
   }
 
+private:
   typedef HashTableTy::const_iterator iterator;
   typedef HashTableTy::const_iterator const_iterator;
   
   iterator begin() const { return HashTable.begin(); }
   iterator end() const   { return HashTable.end(); }
+public:
   
   unsigned size() const { return HashTable.size(); }