set up the machinery for a MacroArgs cache hanging off Preprocessor.

We creating and free thousands of MacroArgs objects (and the related
std::vectors hanging off them) for the testcase in PR5610 even though
there are only ~20 live at a time.  This doesn't actually use the 
cache yet.

llvm-svn: 91391

clang/include/clang/Lex/Preprocessor.h

@@ -177,8 +177,14 @@ class Preprocessor {
 
   /// MICache - A "freelist" of MacroInfo objects that can be reused for quick
   /// allocation.
+  /// FIXME: why not use a singly linked list?
   std::vector<MacroInfo*> MICache;
   
+  /// MacroArgCache - This is a "freelist" of MacroArg objects that can be
+  /// reused for quick allocation.
+  MacroArgs *MacroArgCache;
+  friend class MacroArgs;
+
   // Various statistics we track for performance analysis.
   unsigned NumDirectives, NumIncluded, NumDefined, NumUndefined, NumPragma;
   unsigned NumIf, NumElse, NumEndif;

clang/lib/Lex/MacroArgs.cpp

@@ -48,6 +48,19 @@ void MacroArgs::destroy(Preprocessor &PP) {
   free(this);
 }
 
+/// deallocate - This should only be called by the Preprocessor when managing
+/// its freelist.
+MacroArgs *MacroArgs::deallocate() {
+  MacroArgs *Next = ArgCache;
+  
+  // Run the dtor to deallocate the vectors.
+  this->~MacroArgs();
+  // Release the memory for the object.
+  free(this);
+  
+  return Next;
+}
+
 
 /// getArgLength - Given a pointer to an expanded or unexpanded argument,
 /// return the number of tokens, not counting the EOF, that make up the

clang/lib/Lex/MacroArgs.h

@@ -46,8 +46,12 @@ class MacroArgs {
   /// stringified form of an argument has not yet been computed, this is empty.
   std::vector<Token> StringifiedArgs;
 
+  /// ArgCache - This is a linked list of MacroArgs objects that the
+  /// Preprocessor owns which we use to avoid thrashing malloc/free.
+  MacroArgs *ArgCache;
+  
   MacroArgs(unsigned NumToks, bool varargsElided)
-    : NumUnexpArgTokens(NumToks), VarargsElided(varargsElided) {}
+    : NumUnexpArgTokens(NumToks), VarargsElided(varargsElided), ArgCache(0) {}
   ~MacroArgs() {}
 public:
   /// MacroArgs ctor function - Create a new MacroArgs object with the specified
@@ -103,6 +107,11 @@ public:
   ///
   static Token StringifyArgument(const Token *ArgToks,
                                  Preprocessor &PP, bool Charify = false);
+  
+  
+  /// deallocate - This should only be called by the Preprocessor when managing
+  /// its freelist.
+  MacroArgs *deallocate();
 };
 
 }  // end namespace clang

clang/lib/Lex/Preprocessor.cpp

@@ -26,6 +26,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "clang/Lex/Preprocessor.h"
+#include "MacroArgs.h"
 #include "clang/Lex/HeaderSearch.h"
 #include "clang/Lex/MacroInfo.h"
 #include "clang/Lex/Pragma.h"
@@ -51,7 +52,7 @@ Preprocessor::Preprocessor(Diagnostic &diags, const LangOptions &opts,
   : Diags(&diags), Features(opts), Target(target),FileMgr(Headers.getFileMgr()),
     SourceMgr(SM), HeaderInfo(Headers), Identifiers(opts, IILookup),
     BuiltinInfo(Target), CodeCompletionFile(0), CurPPLexer(0), CurDirLookup(0),
-    Callbacks(0) {
+    Callbacks(0), MacroArgCache(0) {
   ScratchBuf = new ScratchBuffer(SourceMgr);
   CounterValue = 0; // __COUNTER__ starts at 0.
   OwnsHeaderSearch = OwnsHeaders;
@@ -112,6 +113,10 @@ Preprocessor::~Preprocessor() {
   for (unsigned i = 0, e = NumCachedTokenLexers; i != e; ++i)
     delete TokenLexerCache[i];
   
+  // Free any cached MacroArgs.
+  for (MacroArgs *ArgList = MacroArgCache; ArgList; )
+    ArgList = ArgList->deallocate();
+
   // Release pragma information.
   delete PragmaHandlers;