Introduce a caching mechanism for macro expanded tokens.

Previously macro expanded tokens were added to Preprocessor's bump allocator and never released,
even after the TokenLexer that were lexing them was finished, thus they were wasting memory.
A very "useful" boost library was causing clang to eat 1 GB just for the expanded macro tokens.

Introduce a special cache that works like a stack; a TokenLexer can add the macro expanded tokens
in the cache, and when it finishes, the tokens are removed from the end of the cache.

Now consumed memory by expanded tokens for that library is ~ 1.5 MB.

Part of rdar://9327049.

llvm-svn: 134105

4 files changed, 53 insertions, 10 deletions

diff --git a/clang/lib/Lex/PPLexerChange.cpp b/clang/lib/Lex/PPLexerChange.cpp
index bf0a7fbfef1..bf28199b888 100644
--- a/clang/lib/Lex/PPLexerChange.cpp
+++ b/clang/lib/Lex/PPLexerChange.cpp
@@ -265,6 +265,10 @@ bool Preprocessor::HandleEndOfTokenLexer(Token &Result) {
   assert(CurTokenLexer && !CurPPLexer &&
          "Ending a macro when currently in a #include file!");
 
+  if (!MacroExpandingLexersStack.empty() &&
+      MacroExpandingLexersStack.back().first == CurTokenLexer.get())
+    removeCachedMacroExpandedTokensOfLastLexer();
+
   // Delete or cache the now-dead macro expander.
   if (NumCachedTokenLexers == TokenLexerCacheSize)
     CurTokenLexer.reset();
diff --git a/clang/lib/Lex/PPMacroExpansion.cpp b/clang/lib/Lex/PPMacroExpansion.cpp
index 9e8533a4484..d7c4defb368 100644
--- a/clang/lib/Lex/PPMacroExpansion.cpp
+++ b/clang/lib/Lex/PPMacroExpansion.cpp
@@ -22,6 +22,7 @@
 #include "clang/Lex/CodeCompletionHandler.h"
 #include "clang/Lex/ExternalPreprocessorSource.h"
 #include "llvm/ADT/StringSwitch.h"
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/Config/config.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cstdio>
@@ -490,6 +491,46 @@ MacroArgs *Preprocessor::ReadFunctionLikeMacroArgs(Token &MacroName,
                            isVarargsElided, *this);
 }
 
+/// \brief Keeps macro expanded tokens for TokenLexers.
+//
+/// Works like a stack; a TokenLexer adds the macro expanded tokens that is
+/// going to lex in the cache and when it finishes the tokens are removed
+/// from the end of the cache.
+Token *Preprocessor::cacheMacroExpandedTokens(TokenLexer *tokLexer,
+                                              llvm::ArrayRef<Token> tokens) {
+  assert(tokLexer);
+  if (tokens.empty())
+    return 0;
+
+  size_t newIndex = MacroExpandedTokens.size();
+  bool cacheNeedsToGrow = tokens.size() >
+                      MacroExpandedTokens.capacity()-MacroExpandedTokens.size(); 
+  MacroExpandedTokens.append(tokens.begin(), tokens.end());
+
+  if (cacheNeedsToGrow) {
+    // Go through all the TokenLexers whose 'Tokens' pointer points in the
+    // buffer and update the pointers to the (potential) new buffer array.
+    for (unsigned i = 0, e = MacroExpandingLexersStack.size(); i != e; ++i) {
+      TokenLexer *prevLexer;
+      size_t tokIndex;
+      llvm::tie(prevLexer, tokIndex) = MacroExpandingLexersStack[i];
+      prevLexer->Tokens = MacroExpandedTokens.data() + tokIndex;
+    }
+  }
+
+  MacroExpandingLexersStack.push_back(std::make_pair(tokLexer, newIndex));
+  return MacroExpandedTokens.data() + newIndex;
+}
+
+void Preprocessor::removeCachedMacroExpandedTokensOfLastLexer() {
+  assert(!MacroExpandingLexersStack.empty());
+  size_t tokIndex = MacroExpandingLexersStack.back().second;
+  assert(tokIndex < MacroExpandedTokens.size());
+  // Pop the cached macro expanded tokens from the end.
+  MacroExpandedTokens.resize(tokIndex);
+  MacroExpandingLexersStack.pop_back();
+}
+
 /// ComputeDATE_TIME - Compute the current time, enter it into the specified
 /// scratch buffer, then return DATELoc/TIMELoc locations with the position of
 /// the identifier tokens inserted.
diff --git a/clang/lib/Lex/Preprocessor.cpp b/clang/lib/Lex/Preprocessor.cpp
index 48a23880f36..2f43c8e30be 100644
--- a/clang/lib/Lex/Preprocessor.cpp
+++ b/clang/lib/Lex/Preprocessor.cpp
@@ -118,6 +118,8 @@ Preprocessor::Preprocessor(Diagnostic &diags, const LangOptions &opts,
 
 Preprocessor::~Preprocessor() {
   assert(BacktrackPositions.empty() && "EnableBacktrack/Backtrack imbalance!");
+  assert(MacroExpandingLexersStack.empty() && MacroExpandedTokens.empty() &&
+         "Preprocessor::HandleEndOfTokenLexer should have cleared those");
 
   while (!IncludeMacroStack.empty()) {
     delete IncludeMacroStack.back().TheLexer;
@@ -226,7 +228,7 @@ Preprocessor::macro_begin(bool IncludeExternalMacros) const {
 }
 
 size_t Preprocessor::getTotalMemory() const {
-  return BP.getTotalMemory();
+  return BP.getTotalMemory() + MacroExpandedTokens.capacity()*sizeof(Token);
 }
 
 Preprocessor::macro_iterator
diff --git a/clang/lib/Lex/TokenLexer.cpp b/clang/lib/Lex/TokenLexer.cpp
index e7cff8bdc3f..f30c44e0e64 100644
--- a/clang/lib/Lex/TokenLexer.cpp
+++ b/clang/lib/Lex/TokenLexer.cpp
@@ -284,15 +284,11 @@ void TokenLexer::ExpandFunctionArguments() {
     assert(!OwnsTokens && "This would leak if we already own the token list");
     // This is deleted in the dtor.
     NumTokens = ResultToks.size();
-    llvm::BumpPtrAllocator &Alloc = PP.getPreprocessorAllocator();
-    Token *Res =
-      static_cast<Token *>(Alloc.Allocate(sizeof(Token)*ResultToks.size(),
-                                          llvm::alignOf<Token>()));
-    if (NumTokens)
-      memcpy(Res, &ResultToks[0], NumTokens*sizeof(Token));
-    Tokens = Res;
-
-    // The preprocessor bump pointer owns these tokens, not us.
+    // The tokens will be added to Preprocessor's cache and will be removed
+    // when this TokenLexer finishes lexing them.
+    Tokens = PP.cacheMacroExpandedTokens(this, ResultToks);
+
+    // The preprocessor cache of macro expanded tokens owns these tokens,not us.
     OwnsTokens = false;
   }
 }