From c8456f8c593a0db19bc6827adefa3f3dbf2e9b2d Mon Sep 17 00:00:00 2001
From: Ted Kremenek <kremenek@apple.com>
Date: Tue, 19 Oct 2010 22:15:20 +0000
Subject: [PATCH] Really^2 fix <rdar://problem/8361834>, this time without
 crashing.

Now MICache is a linked list (per the FIXME), where we tradeoff between MacroInfo objects being in MICache
and MIChainHead.  MacroInfo objects in the MICache chain are already "Destroy()'ed", so they can be reused.  When
inserting into MICache, we need to remove them from the regular linked list so that they aren't destroyed more than
once.

llvm-svn: 116869
---
 clang/include/clang/Lex/Preprocessor.h | 10 +++---
 clang/lib/Lex/PPDirectives.cpp         | 44 ++++++++++++++++++--------
 clang/lib/Lex/Preprocessor.cpp         |  3 +-
 3 files changed, 38 insertions(+), 19 deletions(-)

diff --git a/clang/include/clang/Lex/Preprocessor.h b/clang/include/clang/Lex/Preprocessor.h
index a1a68dce4517..42e2daac2f26 100644
--- a/clang/include/clang/Lex/Preprocessor.h
+++ b/clang/include/clang/Lex/Preprocessor.h
@@ -195,11 +195,6 @@ class Preprocessor {
   /// to the actual definition of the macro.
   llvm::DenseMap<IdentifierInfo*, MacroInfo*> Macros;
 
-  /// 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;
@@ -255,12 +250,17 @@ private:  // Cached tokens state.
   struct MacroInfoChain {
     MacroInfo MI;
     MacroInfoChain *Next;
+    MacroInfoChain *Prev;
   };
 
   /// MacroInfos are managed as a chain for easy disposal.  This is the head
   /// of that list.
   MacroInfoChain *MIChainHead;
 
+  /// MICache - A "freelist" of MacroInfo objects that can be reused for quick
+  /// allocation.
+  MacroInfoChain *MICache;
+
 public:
   Preprocessor(Diagnostic &diags, const LangOptions &opts,
                const TargetInfo &target,
diff --git a/clang/lib/Lex/PPDirectives.cpp b/clang/lib/Lex/PPDirectives.cpp
index b958d9e489fb..8f66d99b187e 100644
--- a/clang/lib/Lex/PPDirectives.cpp
+++ b/clang/lib/Lex/PPDirectives.cpp
@@ -28,18 +28,23 @@ using namespace clang;
 //===----------------------------------------------------------------------===//
 
 MacroInfo *Preprocessor::AllocateMacroInfo() {
-  MacroInfo *MI;
+  MacroInfoChain *MIChain;
 
-  if (!MICache.empty()) {
-    MI = MICache.back();
-    MICache.pop_back();
-  } else {
-    MacroInfoChain *MIChain = BP.Allocate<MacroInfoChain>();
-    MIChain->Next = MIChainHead;
-    MIChainHead = MIChain;
-    MI = &(MIChain->MI);
+  if (MICache) {
+    MIChain = MICache;
+    MICache = MICache->Next;
   }
-  return MI;
+  else {
+    MIChain = BP.Allocate<MacroInfoChain>();
+  }
+
+  MIChain->Next = MIChainHead;
+  MIChain->Prev = 0;
+  if (MIChainHead)
+    MIChainHead->Prev = MIChain;
+  MIChainHead = MIChain;
+
+  return &(MIChain->MI);
 }
 
 MacroInfo *Preprocessor::AllocateMacroInfo(SourceLocation L) {
@@ -57,10 +62,23 @@ MacroInfo *Preprocessor::CloneMacroInfo(const MacroInfo &MacroToClone) {
 /// ReleaseMacroInfo - Release the specified MacroInfo.  This memory will
 ///  be reused for allocating new MacroInfo objects.
 void Preprocessor::ReleaseMacroInfo(MacroInfo *MI) {
-  MICache.push_back(MI);
-  MI->FreeArgumentList();
-}
+  MacroInfoChain *MIChain = (MacroInfoChain*) MI;
+  if (MacroInfoChain *Prev = MIChain->Prev) {
+    MacroInfoChain *Next = MIChain->Next;
+    Prev->Next = Next;
+    if (Next)
+      Next->Prev = Prev;
+  }
+  else {
+    assert(MIChainHead == MIChain);
+    MIChainHead = MIChain->Next;
+    MIChainHead->Prev = 0;
+  }
+  MIChain->Next = MICache;
+  MICache = MIChain;
 
+  MI->Destroy();
+}
 
 /// DiscardUntilEndOfDirective - Read and discard all tokens remaining on the
 /// current line until the tok::eom token is found.
diff --git a/clang/lib/Lex/Preprocessor.cpp b/clang/lib/Lex/Preprocessor.cpp
index a0782aa86818..1be22df6b1cb 100644
--- a/clang/lib/Lex/Preprocessor.cpp
+++ b/clang/lib/Lex/Preprocessor.cpp
@@ -56,7 +56,8 @@ Preprocessor::Preprocessor(Diagnostic &diags, const LangOptions &opts,
     SourceMgr(SM), HeaderInfo(Headers), ExternalSource(0),
     Identifiers(opts, IILookup), BuiltinInfo(Target), CodeComplete(0),
     CodeCompletionFile(0), SkipMainFilePreamble(0, true), CurPPLexer(0), 
-    CurDirLookup(0), Callbacks(0), MacroArgCache(0), Record(0), MIChainHead(0) {
+    CurDirLookup(0), Callbacks(0), MacroArgCache(0), Record(0), MIChainHead(0),
+    MICache(0) {
   ScratchBuf = new ScratchBuffer(SourceMgr);
   CounterValue = 0; // __COUNTER__ starts at 0.
   OwnsHeaderSearch = OwnsHeaders;