3 files changed, 56 insertions, 9 deletions

diff --git a/lib/Lex/MacroInfo.cpp b/lib/Lex/MacroInfo.cpp
index 7e538fabf4..904f04e4f8 100644
--- a/lib/Lex/MacroInfo.cpp
+++ b/lib/Lex/MacroInfo.cpp
@@ -32,7 +32,8 @@ MacroInfo::MacroInfo(SourceLocation DefLoc)
     IsAllowRedefinitionsWithoutWarning(false),
     IsWarnIfUnused(false),
     IsPublic(true),
-    IsHidden(false) {
+    IsHidden(false),
+    IsAmbiguous(false) {
 }
 
 MacroInfo::MacroInfo(const MacroInfo &MI, llvm::BumpPtrAllocator &PPAllocator)
@@ -56,7 +57,8 @@ MacroInfo::MacroInfo(const MacroInfo &MI, llvm::BumpPtrAllocator &PPAllocator)
     IsAllowRedefinitionsWithoutWarning(MI.IsAllowRedefinitionsWithoutWarning),
     IsWarnIfUnused(MI.IsWarnIfUnused),
     IsPublic(MI.IsPublic),
-    IsHidden(MI.IsHidden) {
+    IsHidden(MI.IsHidden),
+    IsAmbiguous(MI.IsAmbiguous) {
   setArgumentList(MI.ArgumentList, MI.NumArguments, PPAllocator);
 }
 
diff --git a/lib/Lex/PPMacroExpansion.cpp b/lib/Lex/PPMacroExpansion.cpp
index c717816650..dc3a45652a 100644
--- a/lib/Lex/PPMacroExpansion.cpp
+++ b/lib/Lex/PPMacroExpansion.cpp
@@ -89,15 +89,25 @@ void Preprocessor::addLoadedMacroInfo(IdentifierInfo *II, MacroInfo *MI,
     // Find the end of the definition chain.
     MacroInfo *Prev = StoredMI;
     MacroInfo *PrevPrev;
-    bool Ambiguous = false;
+    bool Ambiguous = StoredMI->isAmbiguous();
+    bool MatchedOther = false;
     do {
       // If the macros are not identical, we have an ambiguity.
-      if (!Prev->isIdenticalTo(*MI, *this))
-        Ambiguous = true;
+      if (!Prev->isIdenticalTo(*MI, *this)) {
+        if (!Ambiguous) {
+          Ambiguous = true;
+          StoredMI->setAmbiguous(true);
+        }
+      } else {
+        MatchedOther = true;
+      }
     } while ((PrevPrev = Prev->getPreviousDefinition()) &&
              PrevPrev->isDefined());
 
-    // FIXME: Actually use the ambiguity information for something.
+    // If there are ambiguous definitions, and we didn't match any other
+    // definition, then mark us as ambiguous.
+    if (Ambiguous && !MatchedOther)
+      MI->setAmbiguous(true);
 
     // Wire this macro information into the chain.
     MI->setPreviousDefinition(Prev->getPreviousDefinition());
@@ -360,7 +370,23 @@ bool Preprocessor::HandleMacroExpandedIdentifier(Token &Identifier,
       }
     }
   }
-  
+
+  // If the macro definition is ambiguous, complain.
+  if (MI->isAmbiguous()) {
+    Diag(Identifier, diag::warn_pp_ambiguous_macro)
+      << Identifier.getIdentifierInfo();
+    Diag(MI->getDefinitionLoc(), diag::note_pp_ambiguous_macro_chosen)
+      << Identifier.getIdentifierInfo();
+    for (MacroInfo *PrevMI = MI->getPreviousDefinition();
+         PrevMI && PrevMI->isDefined();
+         PrevMI = PrevMI->getPreviousDefinition()) {
+      if (PrevMI->isAmbiguous()) {
+        Diag(PrevMI->getDefinitionLoc(), diag::note_pp_ambiguous_macro_other)
+          << Identifier.getIdentifierInfo();
+      }
+    }
+  }
+
   // If we started lexing a macro, enter the macro expansion body.
 
   // If this macro expands to no tokens, don't bother to push it onto the
diff --git a/lib/Serialization/ASTReader.cpp b/lib/Serialization/ASTReader.cpp
index 5657ee23bc..8f18eb8465 100644
--- a/lib/Serialization/ASTReader.cpp
+++ b/lib/Serialization/ASTReader.cpp
@@ -1254,6 +1254,24 @@ void ASTReader::ReadMacroRecord(ModuleFile &F, uint64_t Offset,
   SmallVector<IdentifierInfo*, 16> MacroArgs;
   MacroInfo *Macro = 0;
 
+  // RAII object to add the loaded macro information once we're done
+  // adding tokens.
+  struct AddLoadedMacroInfoRAII {
+    Preprocessor &PP;
+    MacroInfo *Hint;
+    MacroInfo *MI;
+    IdentifierInfo *II;
+
+    AddLoadedMacroInfoRAII(Preprocessor &PP, MacroInfo *Hint)
+      : PP(PP), Hint(Hint), MI(), II() { }
+    ~AddLoadedMacroInfoRAII( ) {
+      if (MI) {
+        // Finally, install the macro.
+        PP.addLoadedMacroInfo(II, MI, Hint);
+      }
+    }
+  } AddLoadedMacroInfo(PP, Hint);
+
   while (true) {
     unsigned Code = Stream.ReadCode();
     switch (Code) {
@@ -1370,8 +1388,9 @@ void ASTReader::ReadMacroRecord(ModuleFile &F, uint64_t Offset,
       }
       MI->setHidden(Hidden);
 
-      // Finally, install the macro.
-      PP.addLoadedMacroInfo(II, MI, Hint);
+      // Make sure we install the macro once we're done.
+      AddLoadedMacroInfo.MI = MI;
+      AddLoadedMacroInfo.II = II;
 
       // Remember that we saw this macro last so that we add the tokens that
       // form its body to it.