From e740089d297199c43085e680cee0293c1af73193 Mon Sep 17 00:00:00 2001
From: Douglas Gregor <dgregor@apple.com>
Date: Thu, 11 Oct 2012 17:41:54 +0000
Subject: [PATCH] Introduce a simple "hint" scheme to eliminate the quadratic
 behavior associated with deserializing macro history for an identifier.

llvm-svn: 165729
---
 clang/include/clang/Lex/Preprocessor.h        |  3 ++-
 clang/include/clang/Serialization/ASTReader.h |  4 ++--
 clang/lib/Lex/PPMacroExpansion.cpp            |  6 +++---
 clang/lib/Serialization/ASTReader.cpp         | 12 +++++++-----
 4 files changed, 14 insertions(+), 11 deletions(-)

diff --git a/clang/include/clang/Lex/Preprocessor.h b/clang/include/clang/Lex/Preprocessor.h
index 2c0814c91073..7888a26fcbda 100644
--- a/clang/include/clang/Lex/Preprocessor.h
+++ b/clang/include/clang/Lex/Preprocessor.h
@@ -519,7 +519,8 @@ public:
   /// \brief Specify a macro for this identifier.
   void setMacroInfo(IdentifierInfo *II, MacroInfo *MI);
   /// \brief Add a MacroInfo that was loaded from an AST file.
-  void addLoadedMacroInfo(IdentifierInfo *II, MacroInfo *MI);
+  void addLoadedMacroInfo(IdentifierInfo *II, MacroInfo *MI,
+                          MacroInfo *Hint = 0);
   /// \brief Make the given MacroInfo, that was loaded from an AST file and
   /// previously hidden, visible.
   void makeLoadedMacroInfoVisible(IdentifierInfo *II, MacroInfo *MI);
diff --git a/clang/include/clang/Serialization/ASTReader.h b/clang/include/clang/Serialization/ASTReader.h
index 2a9afc92e9b8..4e8531a820eb 100644
--- a/clang/include/clang/Serialization/ASTReader.h
+++ b/clang/include/clang/Serialization/ASTReader.h
@@ -1433,7 +1433,7 @@ public:
                                                     unsigned LocalID);
 
   /// \brief Retrieve the macro with the given ID.
-  MacroInfo *getMacro(serialization::MacroID ID);
+  MacroInfo *getMacro(serialization::MacroID ID, MacroInfo *Hint = 0);
 
   /// \brief Retrieve the global macro ID corresponding to the given local
   /// ID within the given module file.
@@ -1582,7 +1582,7 @@ public:
   Expr *ReadSubExpr();
 
   /// \brief Reads the macro record located at the given offset.
-  void ReadMacroRecord(ModuleFile &F, uint64_t Offset);
+  void ReadMacroRecord(ModuleFile &F, uint64_t Offset, MacroInfo *Hint = 0);
 
   /// \brief Determine the global preprocessed entity ID that corresponds to
   /// the given local ID within the given module.
diff --git a/clang/lib/Lex/PPMacroExpansion.cpp b/clang/lib/Lex/PPMacroExpansion.cpp
index 8db74f28d414..c7178166507a 100644
--- a/clang/lib/Lex/PPMacroExpansion.cpp
+++ b/clang/lib/Lex/PPMacroExpansion.cpp
@@ -55,7 +55,8 @@ void Preprocessor::setMacroInfo(IdentifierInfo *II, MacroInfo *MI) {
     II->setChangedSinceDeserialization();
 }
 
-void Preprocessor::addLoadedMacroInfo(IdentifierInfo *II, MacroInfo *MI) {
+void Preprocessor::addLoadedMacroInfo(IdentifierInfo *II, MacroInfo *MI,
+                                      MacroInfo *Hint) {
   assert(MI && "Missing macro?");
   assert(MI->isFromAST() && "Macro is not from an AST?");
   assert(!MI->getPreviousDefinition() && "Macro already in chain?");
@@ -105,8 +106,7 @@ void Preprocessor::addLoadedMacroInfo(IdentifierInfo *II, MacroInfo *MI) {
   }
 
   // The macro is not a definition; put it at the end of the list.
-  // FIXME: Adding macro history is quadratic, but a hint could fix this.
-  MacroInfo *Prev = StoredMI;
+  MacroInfo *Prev = Hint? Hint : StoredMI;
   while (Prev->getPreviousDefinition())
     Prev = Prev->getPreviousDefinition();
   Prev->setPreviousDefinition(MI);
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index 736f082d6f38..5657ee23bc12 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -1241,7 +1241,8 @@ bool ASTReader::ReadBlockAbbrevs(llvm::BitstreamCursor &Cursor,
   }
 }
 
-void ASTReader::ReadMacroRecord(ModuleFile &F, uint64_t Offset) {
+void ASTReader::ReadMacroRecord(ModuleFile &F, uint64_t Offset,
+                                MacroInfo *Hint) {
   llvm::BitstreamCursor &Stream = F.MacroCursor;
 
   // Keep track of where we are in the stream, then jump back there
@@ -1370,7 +1371,7 @@ void ASTReader::ReadMacroRecord(ModuleFile &F, uint64_t Offset) {
       MI->setHidden(Hidden);
 
       // Finally, install the macro.
-      PP.addLoadedMacroInfo(II, MI);
+      PP.addLoadedMacroInfo(II, MI, Hint);
 
       // Remember that we saw this macro last so that we add the tokens that
       // form its body to it.
@@ -5795,7 +5796,7 @@ IdentifierID ASTReader::getGlobalIdentifierID(ModuleFile &M, unsigned LocalID) {
   return LocalID + I->second;
 }
 
-MacroInfo *ASTReader::getMacro(MacroID ID) {
+MacroInfo *ASTReader::getMacro(MacroID ID, MacroInfo *Hint) {
   if (ID == 0)
     return 0;
 
@@ -5811,7 +5812,7 @@ MacroInfo *ASTReader::getMacro(MacroID ID) {
     assert(I != GlobalMacroMap.end() && "Corrupted global macro map");
     ModuleFile *M = I->second;
     unsigned Index = ID - M->BaseMacroID;
-    ReadMacroRecord(*M, M->MacroOffsets[Index]);
+    ReadMacroRecord(*M, M->MacroOffsets[Index], Hint);
   }
 
   return MacrosLoaded[ID];
@@ -6512,9 +6513,10 @@ void ASTReader::finishPendingActions() {
     for (unsigned I = 0; I != PendingMacroIDs.size(); ++I) {
       // FIXME: std::move here
       SmallVector<MacroID, 2> GlobalIDs = PendingMacroIDs.begin()[I].second;
+      MacroInfo *Hint = 0;
       for (unsigned IDIdx = 0, NumIDs = GlobalIDs.size(); IDIdx !=  NumIDs;
            ++IDIdx) {
-        getMacro(GlobalIDs[IDIdx]);
+        Hint = getMacro(GlobalIDs[IDIdx], Hint);
       }
     }
     PendingMacroIDs.clear();