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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226467 91177308-0d34-0410-b5e6-96231b3b80d8

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));

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 {

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()) &&
+  if ((EmitUniquedSection && !Kind.isCommon()) || GV->hasComdat()) {
-      !Kind.isCommon()) {
     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)) {
-      if (const Comdat *C = getELFComdat(GV))
-        Group = C->getName();
-      else
-        Group = Name.substr(Prefix.size());
       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
+  if ((EmitUniquedSection && !Kind.isCommon()) || GV->hasComdat()) {
-  // 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()) {
     const char *Name = getCOFFSectionNameForUniqueGlobal(Kind);
     unsigned Characteristics = getCOFFSectionFlags(Kind);
 

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);

test/Bitcode/linkage-types-3.2.ll

@@ -33,13 +33,13 @@
 ; CHECK: @available_externally.var = available_externally constant i32 0{{$}}
 
 @linkonce.var = linkonce constant i32 0
-; CHECK: @linkonce.var = linkonce constant i32 0{{$}}
+; CHECK: @linkonce.var = linkonce constant i32 0, comdat{{$}}
 
 @weak.var = weak constant i32 0
-; CHECK: @weak.var = weak constant i32 0{{$}}
+; CHECK: @weak.var = weak constant i32 0, comdat{{$}}
 
 @linkonce_odr.var = linkonce_odr constant i32 0
-; CHECK: @linkonce_odr.var = linkonce_odr constant i32 0{{$}}
+; CHECK: @linkonce_odr.var = linkonce_odr constant i32 0, comdat{{$}}
 
 @linkonce_odr_auto_hide.var = linkonce_odr_auto_hide constant i32 0
 ; CHECK: @linkonce_odr_auto_hide.var = constant i32 0{{$}}
@@ -90,19 +90,19 @@ define available_externally void @available_externally()
 }
 
 define linkonce void @linkonce()
-; CHECK: define linkonce void @linkonce() {
+; CHECK: define linkonce void @linkonce() comdat {
 {
   ret void
 }
 
 define weak void @weak()
-; CHECK: define weak void @weak() {
+; CHECK: define weak void @weak() comdat {
 {
   ret void
 }
 
 define linkonce_odr void @linkonce_odr()
-; CHECK: define linkonce_odr void @linkonce_odr() {
+; CHECK: define linkonce_odr void @linkonce_odr() comdat {
 {
   ret void
 }

test/CodeGen/ARM/odr_comdat.ll

@@ -1,16 +0,0 @@
-; RUN: llc < %s -mtriple=arm-linux-gnueabi | FileCheck %s -check-prefix=ARMGNUEABI
-
-; Checking that a comdat group gets generated correctly for a static member 
-; of instantiated C++ templates.
-; see http://sourcery.mentor.com/public/cxx-abi/abi.html#vague-itemplate
-; section 5.2.6 Instantiated templates
-; "Any static member data object is emitted in a COMDAT identified by its mangled 
-;  name, in any object file with a reference to its name symbol."
-
-; Case 1: variable is not explicitly initialized, and ends up in a .bss section
-; ARMGNUEABI: .section        .bss._ZN1CIiE1iE,"aGw",%nobits,_ZN1CIiE1iE,comdat
-@_ZN1CIiE1iE = weak_odr global i32 0, align 4
-
-; Case 2: variable is explicitly initialized, and ends up in a .data section
-; ARMGNUEABI: .section        .data._ZN1CIiE1jE,"aGw",%progbits,_ZN1CIiE1jE,comdat
-@_ZN1CIiE1jE = weak_odr global i32 12, align 4

test/CodeGen/ARM/section-name.ll

@@ -16,7 +16,7 @@ entry:
   ret void
 }
 
-; CHECK: .section .text.test3,"axG",%progbits,test3,comdat
+; CHECK: .text
 ; CHECK: .weak test3
 ; CHECK: .type test3,%function
 define linkonce_odr void @test3() {

test/CodeGen/X86/dllexport-x86_64.ll

@@ -17,19 +17,16 @@ define dllexport void @f2() unnamed_addr {
 	ret void
 }
 
-; CHECK: .section .text,"xr",discard,lnk1
 ; CHECK: .globl lnk1
 define linkonce_odr dllexport void @lnk1() {
 	ret void
 }
 
-; CHECK: .section .text,"xr",discard,lnk2
 ; CHECK: .globl lnk2
 define linkonce_odr dllexport void @lnk2() alwaysinline {
 	ret void
 }
 
-; CHECK: .section .text,"xr",discard,weak1
 ; CHECK: .globl weak1
 define weak_odr dllexport void @weak1() {
 	ret void
@@ -47,11 +44,9 @@ define weak_odr dllexport void @weak1() {
 ; CHECK: .comm Var3
 @Var3 = common dllexport global i32 0, align 4
 
-; CHECK: .section .data,"wd",discard,WeakVar1
 ; CHECK: .globl WeakVar1
 @WeakVar1 = weak_odr dllexport global i32 1, align 4
 
-; CHECK: .section .rdata,"rd",discard,WeakVar2
 ; CHECK: .globl WeakVar2
 @WeakVar2 = weak_odr dllexport unnamed_addr constant i32 1
 

test/CodeGen/X86/dllexport.ll

@@ -36,19 +36,16 @@ define dllexport x86_thiscallcc void @thisfun() nounwind {
 	ret void
 }
 
-; CHECK: .section .text,"xr",discard,_lnk1
 ; CHECK: .globl _lnk1
 define linkonce_odr dllexport void @lnk1() {
 	ret void
 }
 
-; CHECK: .section .text,"xr",discard,_lnk2
 ; CHECK: .globl _lnk2
 define linkonce_odr dllexport void @lnk2() alwaysinline {
 	ret void
 }
 
-; CHECK: .section .text,"xr",discard,_weak1
 ; CHECK: .globl _weak1
 define weak_odr dllexport void @weak1() {
 	ret void
@@ -66,11 +63,9 @@ define weak_odr dllexport void @weak1() {
 ; CHECK: .comm _Var3
 @Var3 = common dllexport global i32 0, align 4
 
-; CHECK: .section .data,"wd",discard,_WeakVar1
 ; CHECK: .globl _WeakVar1
 @WeakVar1 = weak_odr dllexport global i32 1, align 4
 
-; CHECK: .section .rdata,"rd",discard,_WeakVar2
 ; CHECK: .globl _WeakVar2
 @WeakVar2 = weak_odr dllexport unnamed_addr constant i32 1
 

test/CodeGen/X86/global-sections.ll

@@ -85,7 +85,6 @@ define void @F1() {
 @"foo bar" = linkonce global i32 42
 
 ; LINUX: .type  "foo bar",@object
-; LINUX: .section ".data.foo bar","aGw",@progbits,"foo bar",comdat
 ; LINUX: .weak  "foo bar"
 ; LINUX: "foo bar":
 
@@ -98,7 +97,6 @@ define void @F1() {
 @G6 = weak_odr unnamed_addr constant [1 x i8] c"\01"
 
 ; LINUX:   .type        G6,@object
-; LINUX:   .section     .rodata.G6,"aG",@progbits,G6,comdat
 ; LINUX:   .weak        G6
 ; LINUX: G6:
 ; LINUX:   .byte        1

test/CodeGen/X86/odr_comdat.ll

@@ -1,16 +0,0 @@
-; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu | FileCheck %s -check-prefix=X86LINUX
-
-; Checking that a comdat group gets generated correctly for a static member 
-; of instantiated C++ templates.
-; see http://sourcery.mentor.com/public/cxx-abi/abi.html#vague-itemplate
-; section 5.2.6 Instantiated templates
-; "Any static member data object is emitted in a COMDAT identified by its mangled 
-;  name, in any object file with a reference to its name symbol."
-
-; Case 1: variable is not explicitly initialized, and ends up in a .bss section
-; X86LINUX:   .section        .bss._ZN1CIiE1iE,"aGw",@nobits,_ZN1CIiE1iE,comdat
-@_ZN1CIiE1iE = weak_odr global i32 0, align 4
-
-; Case 2: variable is explicitly initialized, and ends up in a .data section
-; X86LINUX:   .section        .data._ZN1CIiE1jE,"aGw",@progbits,_ZN1CIiE1jE,comdat
-@_ZN1CIiE1jE = weak_odr global i32 12, align 4

test/CodeGen/X86/pic_jumptable.ll

@@ -10,7 +10,7 @@
 
 declare void @_Z3bari(i32)
 
-; CHECK-LINUX: .text._Z3fooILi1EEvi,"axG",@progbits,_Z3fooILi1EEvi,comdat
+; CHECK-LINUX: _Z3fooILi1EEvi:
 define linkonce void @_Z3fooILi1EEvi(i32 %Y) nounwind {
 entry:
 ; CHECK:       L0$pb

test/MC/COFF/bss_section.ll

@@ -5,5 +5,6 @@
 @"\01?thingy@@3Ufoo@@B" = global %struct.foo zeroinitializer, align 4
 ; CHECK: .bss
 
-@thingy_linkonce = linkonce_odr global %struct.foo zeroinitializer, align 4
+$thingy_linkonce = comdat any
+@thingy_linkonce = linkonce_odr global %struct.foo zeroinitializer, comdat, align 4
 ; CHECK: .section .bss,"wb",discard,_thingy_linkonce

test/MC/COFF/const-gv-with-rel-init.ll

@@ -8,4 +8,4 @@ define void @f() {
 ; CHECK:  .section  .CRT$XLB,"rd"
 
 @weak_array = weak_odr unnamed_addr constant [1 x i8*] [i8* bitcast (void ()* @f to i8*)]
-; CHECK:  .section  .rdata,"rd",discard,weak_array
+; CHECK:  .section  .rdata,"rd"

test/MC/COFF/weak-symbol.ll

@@ -1,48 +0,0 @@
-; Test that weak functions and globals are placed into selectany COMDAT
-; sections with the mangled name as suffix. Ensure that the weak linkage
-; type is not ignored by the backend if the section was specialized.
-;
-; RUN: llc -mtriple=i686-pc-win32 %s     -o - | FileCheck %s --check-prefix=X86
-; RUN: llc -mtriple=i686-pc-mingw32 %s   -o - | FileCheck %s --check-prefix=X86
-; RUN: llc -mtriple=x86_64-pc-win32 %s   -o - | FileCheck %s --check-prefix=X64
-; RUN: llc -mtriple=x86_64-pc-mingw32 %s -o - | FileCheck %s --check-prefix=X64
-
-; Mangled function
-; X86: .section .text,"xr",discard,__Z3foo
-; X86: .globl __Z3foo
-;
-; X64: .section .text,"xr",discard,_Z3foo
-; X64: .globl _Z3foo
-define weak void @_Z3foo() {
-  ret void
-}
-
-; Unmangled function
-; X86: .section .sect,"xr",discard,_f
-; X86: .globl _f
-;
-; X64: .section .sect,"xr",discard,f
-; X64: .globl f
-define weak void @f() section ".sect" {
-  ret void
-}
-
-; Weak global
-; X86: .section .data,"rd",discard,_a
-; X86: .globl _a
-; X86: .zero 12
-;
-; X64: .section .data,"rd",discard,a
-; X64: .globl a
-; X64: .zero 12
-@a = weak unnamed_addr constant { i32, i32, i32 } { i32 0, i32 0, i32 0}, section ".data"
-
-; X86:  .section        .tls$,"wd",discard,_b
-; X86:  .globl  _b
-; X86:  .long   0
-;
-; X64:  .section        .tls$,"wd",discard,b
-; X64:  .globl  b
-; X64:  .long   0
-
-@b = weak_odr thread_local global i32 0, align 4