2 files changed, 47 insertions, 19 deletions

diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index 409adafc786..fe48c254d24 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -156,19 +156,27 @@ static bool ConvertToString(ArrayRef<uint64_t> Record, unsigned Idx,
   return false;
 }
 
+static bool hasImplicitComdat(size_t Val) {
+  switch (Val) {
+  default:
+    return false;
+  case 1:  // Old WeakAnyLinkage
+  case 4:  // Old LinkOnceAnyLinkage
+  case 10: // Old WeakODRLinkage
+  case 11: // Old LinkOnceODRLinkage
+    return true;
+  }
+}
+
 static GlobalValue::LinkageTypes getDecodedLinkage(unsigned Val) {
   switch (Val) {
   default: // Map unknown/new linkages to external
   case 0:
     return GlobalValue::ExternalLinkage;
-  case 1:
-    return GlobalValue::WeakAnyLinkage;
   case 2:
     return GlobalValue::AppendingLinkage;
   case 3:
     return GlobalValue::InternalLinkage;
-  case 4:
-    return GlobalValue::LinkOnceAnyLinkage;
   case 5:
     return GlobalValue::ExternalLinkage; // Obsolete DLLImportLinkage
   case 6:
@@ -179,10 +187,6 @@ static GlobalValue::LinkageTypes getDecodedLinkage(unsigned Val) {
     return GlobalValue::CommonLinkage;
   case 9:
     return GlobalValue::PrivateLinkage;
-  case 10:
-    return GlobalValue::WeakODRLinkage;
-  case 11:
-    return GlobalValue::LinkOnceODRLinkage;
   case 12:
     return GlobalValue::AvailableExternallyLinkage;
   case 13:
@@ -191,6 +195,18 @@ static GlobalValue::LinkageTypes getDecodedLinkage(unsigned Val) {
     return GlobalValue::PrivateLinkage; // Obsolete LinkerPrivateWeakLinkage
   case 15:
     return GlobalValue::ExternalLinkage; // Obsolete LinkOnceODRAutoHideLinkage
+  case 1: // Old value with implicit comdat.
+  case 16:
+    return GlobalValue::WeakAnyLinkage;
+  case 10: // Old value with implicit comdat.
+  case 17:
+    return GlobalValue::WeakODRLinkage;
+  case 4: // Old value with implicit comdat.
+  case 18:
+    return GlobalValue::LinkOnceAnyLinkage;
+  case 11: // Old value with implicit comdat.
+  case 19:
+    return GlobalValue::LinkOnceODRLinkage;
   }
 }
 
@@ -1118,6 +1134,10 @@ std::error_code BitcodeReader::ParseValueSymbolTable() {
       Value *V = ValueList[ValueID];
 
       V->setName(StringRef(ValueName.data(), ValueName.size()));
+      if (auto *GO = dyn_cast<GlobalObject>(V)) {
+        if (GO->getComdat() == reinterpret_cast<Comdat *>(1))
+          GO->setComdat(TheModule->getOrInsertComdat(V->getName()));
+      }
       ValueName.clear();
       break;
     }
@@ -2140,7 +2160,8 @@ std::error_code BitcodeReader::ParseModule(bool Resume) {
       Ty = cast<PointerType>(Ty)->getElementType();
 
       bool isConstant = Record[1];
-      GlobalValue::LinkageTypes Linkage = getDecodedLinkage(Record[3]);
+      uint64_t RawLinkage = Record[3];
+      GlobalValue::LinkageTypes Linkage = getDecodedLinkage(RawLinkage);
       unsigned Alignment = (1 << Record[4]) >> 1;
       std::string Section;
       if (Record[5]) {
@@ -2178,7 +2199,7 @@ std::error_code BitcodeReader::ParseModule(bool Resume) {
       if (Record.size() > 10)
         NewGV->setDLLStorageClass(GetDecodedDLLStorageClass(Record[10]));
       else
-        UpgradeDLLImportExportLinkage(NewGV, Record[3]);
+        UpgradeDLLImportExportLinkage(NewGV, RawLinkage);
 
       ValueList.push_back(NewGV);
 
@@ -2186,11 +2207,14 @@ std::error_code BitcodeReader::ParseModule(bool Resume) {
       if (unsigned InitID = Record[2])
         GlobalInits.push_back(std::make_pair(NewGV, InitID-1));
 
-      if (Record.size() > 11)
+      if (Record.size() > 11) {
         if (unsigned ComdatID = Record[11]) {
           assert(ComdatID <= ComdatList.size());
           NewGV->setComdat(ComdatList[ComdatID - 1]);
         }
+      } else if (hasImplicitComdat(RawLinkage)) {
+        NewGV->setComdat(reinterpret_cast<Comdat *>(1));
+      }
       break;
     }
     // FUNCTION:  [type, callingconv, isproto, linkage, paramattr,
@@ -2214,7 +2238,8 @@ std::error_code BitcodeReader::ParseModule(bool Resume) {
 
       Func->setCallingConv(static_cast<CallingConv::ID>(Record[1]));
       bool isProto = Record[2];
-      Func->setLinkage(getDecodedLinkage(Record[3]));
+      uint64_t RawLinkage = Record[3];
+      Func->setLinkage(getDecodedLinkage(RawLinkage));
       Func->setAttributes(getAttributes(Record[4]));
 
       Func->setAlignment((1 << Record[5]) >> 1);
@@ -2242,13 +2267,16 @@ std::error_code BitcodeReader::ParseModule(bool Resume) {
       if (Record.size() > 11)
         Func->setDLLStorageClass(GetDecodedDLLStorageClass(Record[11]));
       else
-        UpgradeDLLImportExportLinkage(Func, Record[3]);
+        UpgradeDLLImportExportLinkage(Func, RawLinkage);
 
-      if (Record.size() > 12)
+      if (Record.size() > 12) {
         if (unsigned ComdatID = Record[12]) {
           assert(ComdatID <= ComdatList.size());
           Func->setComdat(ComdatList[ComdatID - 1]);
         }
+      } else if (hasImplicitComdat(RawLinkage)) {
+        Func->setComdat(reinterpret_cast<Comdat *>(1));
+      }
 
       if (Record.size() > 13 && Record[13] != 0)
         FunctionPrefixes.push_back(std::make_pair(Func, Record[13]-1));
diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
index 5e8c64ee9cd..960a7922cd8 100644
--- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -480,13 +480,13 @@ static unsigned getEncodedLinkage(const GlobalValue &GV) {
   case GlobalValue::ExternalLinkage:
     return 0;
   case GlobalValue::WeakAnyLinkage:
-    return 1;
+    return 16;
   case GlobalValue::AppendingLinkage:
     return 2;
   case GlobalValue::InternalLinkage:
     return 3;
   case GlobalValue::LinkOnceAnyLinkage:
-    return 4;
+    return 18;
   case GlobalValue::ExternalWeakLinkage:
     return 7;
   case GlobalValue::CommonLinkage:
@@ -494,9 +494,9 @@ static unsigned getEncodedLinkage(const GlobalValue &GV) {
   case GlobalValue::PrivateLinkage:
     return 9;
   case GlobalValue::WeakODRLinkage:
-    return 10;
+    return 17;
   case GlobalValue::LinkOnceODRLinkage:
-    return 11;
+    return 19;
   case GlobalValue::AvailableExternallyLinkage:
     return 12;
   }
@@ -629,7 +629,7 @@ static void WriteModuleInfo(const Module *M, const ValueEnumerator &VE,
                               Log2_32_Ceil(MaxGlobalType+1)));
     Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1));      // Constant.
     Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));        // Initializer.
-    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 4));      // Linkage.
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 5));      // Linkage.
     if (MaxAlignment == 0)                                      // Alignment.
       Abbv->Add(BitCodeAbbrevOp(0));
     else {