2 files changed, 10 insertions, 4 deletions
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index da5a0e68e93..2ee4975a468 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -826,7 +826,7 @@ IdentifierInfo *ASTIdentifierLookupTrait::ReadData(const internal_key_type& k,
         uint32_t LocalMacroID =
             endian::readNext<uint32_t, little, unaligned>(d);
         DataLen -= 4;
-        if (LocalMacroID == 0xdeadbeef) break;
+        if (LocalMacroID == (uint32_t)-1) break;
         LocalMacroIDs.push_back(LocalMacroID);
       }
     }
@@ -1807,7 +1807,7 @@ struct ASTReader::ModuleMacroInfo {
 };
 
 ASTReader::ModuleMacroInfo *
-ASTReader::getModuleMacro(const PendingMacroInfo &PMInfo) {
+ASTReader::getModuleMacro(IdentifierInfo *II, const PendingMacroInfo &PMInfo) {
   ModuleMacroInfo Info;
 
   uint32_t ID = PMInfo.ModuleMacroData.MacID;
@@ -1815,6 +1815,11 @@ ASTReader::getModuleMacro(const PendingMacroInfo &PMInfo) {
     // Macro undefinition.
     Info.SubModID = getGlobalSubmoduleID(*PMInfo.M, ID >> 1);
     Info.MI = nullptr;
+
+    // If we've already loaded the #undef of this macro from this module,
+    // don't do so again.
+    if (!LoadedUndefs.insert(std::make_pair(II, Info.SubModID)).second)
+      return nullptr;
   } else {
     // Macro definition.
     GlobalMacroID GMacID = getGlobalMacroID(*PMInfo.M, ID >> 1);
@@ -1848,7 +1853,7 @@ void ASTReader::resolvePendingMacro(IdentifierInfo *II,
 
   // Module Macro.
 
-  ModuleMacroInfo *MMI = getModuleMacro(PMInfo);
+  ModuleMacroInfo *MMI = getModuleMacro(II, PMInfo);
   if (!MMI)
     return;
 
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 3f8db194d06..15e7de48c9b 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -3347,6 +3347,7 @@ public:
     using namespace llvm::support;
     endian::Writer<little> LE(Out);
 
+    assert((uint16_t)DataLen == DataLen && (uint16_t)KeyLen == KeyLen);
     LE.write<uint16_t>(DataLen);
     // We emit the key length after the data length so that every
     // string is preceded by a 16-bit length. This matches the PTH
@@ -3425,7 +3426,7 @@ public:
           }
           emitMacroOverrides(Out, getOverriddenSubmodules(MD, Scratch));
         }
-        LE.write<uint32_t>(0xdeadbeef);
+        LE.write<uint32_t>((uint32_t)-1);
       }
     }