[PCH/Modules] Change how macro [re]definitions are de/serialized.

Previously we would serialize the macro redefinitions as a list, part of
the identifier, and try to chain them together across modules individually
without having the info that they were already chained at definition time.

Change this by serializing the macro redefinition chain and then try
to synthesize the chain parts across modules. This allows us to correctly
pinpoint when 2 different definitions are ambiguous because they came from
unrelated modules.

Fixes bogus "ambiguous expansion of macro" warning when a macro in a PCH
is redefined without undef'ing it first.

rdar://13016031

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172620 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 9 insertions, 16 deletions

diff --git a/lib/Serialization/ASTWriter.cpp b/lib/Serialization/ASTWriter.cpp
index af736a4048..67e03c2334 100644
--- a/lib/Serialization/ASTWriter.cpp
+++ b/lib/Serialization/ASTWriter.cpp
@@ -1796,12 +1796,10 @@ void ASTWriter::WritePreprocessor(const Preprocessor &PP, bool IsModule) {
   // Construct the list of macro definitions that need to be serialized.
   SmallVector<std::pair<const IdentifierInfo *, MacroInfo *>, 2> 
     MacrosToEmit;
-  llvm::SmallPtrSet<const IdentifierInfo*, 4> MacroDefinitionsSeen;
   for (Preprocessor::macro_iterator I = PP.macro_begin(Chain == 0),
                                     E = PP.macro_end(Chain == 0);
        I != E; ++I) {
     if (!IsModule || I->second->isPublic()) {
-      MacroDefinitionsSeen.insert(I->first);
       MacrosToEmit.push_back(std::make_pair(I->first, I->second));
     }
   }
@@ -1854,6 +1852,12 @@ void ASTWriter::WritePreprocessor(const Preprocessor &PP, bool IsModule) {
       Record.push_back(inferSubmoduleIDFromLocation(MI->getDefinitionLoc()));
       AddSourceLocation(MI->getDefinitionLoc(), Record);
       AddSourceLocation(MI->getDefinitionEndLoc(), Record);
+      MacroInfo *PrevMI = MI->getPreviousDefinition();
+      // Serialize only the part of the definition chain that is local.
+      // The chain will be synthesized across modules by the ASTReader.
+      if (Chain && PrevMI && PrevMI->isFromAST())
+        PrevMI = 0;
+      addMacroRef(PrevMI, Record);
       AddSourceLocation(MI->getUndefLoc(), Record);
       Record.push_back(MI->isUsed());
       Record.push_back(MI->isPublic());
@@ -2735,14 +2739,8 @@ public:
     if (isInterestingIdentifier(II, Macro)) {
       DataLen += 2; // 2 bytes for builtin ID
       DataLen += 2; // 2 bytes for flags
-      if (hadMacroDefinition(II, Macro)) {
-        for (MacroInfo *M = Macro; M; M = M->getPreviousDefinition()) {
-          if (Writer.getMacroRef(M) != 0)
-            DataLen += 4;
-        }
-
+      if (hadMacroDefinition(II, Macro))
         DataLen += 4;
-      }
 
       for (IdentifierResolver::iterator D = IdResolver.begin(II),
                                      DEnd = IdResolver.end();
@@ -2787,13 +2785,8 @@ public:
     clang::io::Emit16(Out, Bits);
 
     if (HadMacroDefinition) {
-      // Write all of the macro IDs associated with this identifier.
-      for (MacroInfo *M = Macro; M; M = M->getPreviousDefinition()) {
-        if (MacroID ID = Writer.getMacroRef(M))
-          clang::io::Emit32(Out, ID);
-      }
-
-      clang::io::Emit32(Out, 0);
+      // Write the macro ID associated with this identifier.
+      clang::io::Emit32(Out, Writer.getMacroRef(Macro));
     }
 
     // Emit the declaration IDs in reverse order, because the