Bring r226038 back.

No change in this commit, but clang was changed to also produce trivial comdats when
needed.

Original message:

Don't create new comdats in CodeGen.

This patch stops the implicit creation of comdats during codegen.

Clang now sets the comdat explicitly when it is required. With this patch clang and gcc
now produce the same result in pr19848.

llvm-svn: 226467

4 files changed, 52 insertions, 35 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 {
diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index 9f1e06b4725..b9a3ad23d1f 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -257,8 +257,7 @@ SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
 
   // If this global is linkonce/weak and the target handles this by emitting it
   // into a 'uniqued' section name, create and return the section now.
-  if ((GV->isWeakForLinker() || EmitUniquedSection || GV->hasComdat()) &&
-      !Kind.isCommon()) {
+  if ((EmitUniquedSection && !Kind.isCommon()) || GV->hasComdat()) {
     StringRef Prefix = getSectionPrefixForGlobal(Kind);
 
     SmallString<128> Name(Prefix);
@@ -266,12 +265,9 @@ SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
 
     StringRef Group = "";
     unsigned Flags = getELFSectionFlags(Kind);
-    if (GV->isWeakForLinker() || GV->hasComdat()) {
-      if (const Comdat *C = getELFComdat(GV))
-        Group = C->getName();
-      else
-        Group = Name.substr(Prefix.size());
+    if (const Comdat *C = getELFComdat(GV)) {
       Flags |= ELF::SHF_GROUP;
+      Group = C->getName();
     }
 
     return getContext().getELFSection(Name.str(),
@@ -801,7 +797,7 @@ const MCSection *TargetLoweringObjectFileCOFF::getExplicitSectionGlobal(
   unsigned Characteristics = getCOFFSectionFlags(Kind);
   StringRef Name = GV->getSection();
   StringRef COMDATSymName = "";
-  if ((GV->isWeakForLinker() || GV->hasComdat()) && !Kind.isCommon()) {
+  if (GV->hasComdat()) {
     Selection = getSelectionForCOFF(GV);
     const GlobalValue *ComdatGV;
     if (Selection == COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE)
@@ -848,12 +844,7 @@ SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
   else
     EmitUniquedSection = TM.getDataSections();
 
-  // If this global is linkonce/weak and the target handles this by emitting it
-  // into a 'uniqued' section name, create and return the section now.
-  // Section names depend on the name of the symbol which is not feasible if the
-  // symbol has private linkage.
-  if ((GV->isWeakForLinker() || EmitUniquedSection || GV->hasComdat()) &&
-      !Kind.isCommon()) {
+  if ((EmitUniquedSection && !Kind.isCommon()) || GV->hasComdat()) {
     const char *Name = getCOFFSectionNameForUniqueGlobal(Kind);
     unsigned Characteristics = getCOFFSectionFlags(Kind);
 
diff --git a/llvm/lib/Target/XCore/XCoreAsmPrinter.cpp b/llvm/lib/Target/XCore/XCoreAsmPrinter.cpp
index cbcf05ade82..18e718493c9 100644
--- a/llvm/lib/Target/XCore/XCoreAsmPrinter.cpp
+++ b/llvm/lib/Target/XCore/XCoreAsmPrinter.cpp
@@ -106,7 +106,6 @@ void XCoreAsmPrinter::emitArrayBound(MCSymbol *Sym, const GlobalVariable *GV) {
                                                       OutContext));
     if (GV->hasWeakLinkage() || GV->hasLinkOnceLinkage() ||
         GV->hasCommonLinkage()) {
-      // TODO Use COMDAT groups for LinkOnceLinkage
       OutStreamer.EmitSymbolAttribute(SymGlob, MCSA_Weak);
     }
   }
@@ -141,7 +140,6 @@ void XCoreAsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
     emitArrayBound(GVSym, GV);
     OutStreamer.EmitSymbolAttribute(GVSym, MCSA_Global);
 
-    // TODO Use COMDAT groups for LinkOnceLinkage
     if (GV->hasWeakLinkage() || GV->hasLinkOnceLinkage() ||
         GV->hasCommonLinkage())
       OutStreamer.EmitSymbolAttribute(GVSym, MCSA_Weak);