Start setting dso_local in clang.

This starts adding dso_local to clang.

The hope is to eventually have TargetMachine::shouldAssumeDsoLocal go
away. My objective for now is to move enough of it to clang to remove
the need for the TargetMachine one to handle PIE copy relocations and
-fno-plt. With that it should then be easy to implement a
-fno-copy-reloc in clang.

This patch just adds the cases where we assume a symbol to be local
based on the file being compiled for an executable or a shared
library.

llvm-svn: 324107

6 files changed, 79 insertions, 11 deletions

diff --git a/clang/lib/CodeGen/CGDecl.cpp b/clang/lib/CodeGen/CGDecl.cpp
index 04585a8afbb..5de8691bddb 100644
--- a/clang/lib/CodeGen/CGDecl.cpp
+++ b/clang/lib/CodeGen/CGDecl.cpp
@@ -240,7 +240,7 @@ llvm::Constant *CodeGenModule::getOrCreateStaticVarDecl(
       getModule(), LTy, Ty.isConstant(getContext()), Linkage, Init, Name,
       nullptr, llvm::GlobalVariable::NotThreadLocal, TargetAS);
   GV->setAlignment(getContext().getDeclAlign(&D).getQuantity());
-  setGlobalVisibility(GV, &D, ForDefinition);
+  setGVProperties(GV, &D, ForDefinition);
 
   if (supportsCOMDAT() && GV->isWeakForLinker())
     GV->setComdat(TheModule.getOrInsertComdat(GV->getName()));
@@ -344,6 +344,7 @@ CodeGenFunction::AddInitializerToStaticVarDecl(const VarDecl &D,
                                   OldGV->getThreadLocalMode(),
                            CGM.getContext().getTargetAddressSpace(D.getType()));
     GV->setVisibility(OldGV->getVisibility());
+    GV->setDSOLocal(OldGV->isDSOLocal());
     GV->setComdat(OldGV->getComdat());
 
     // Steal the name of the old global
diff --git a/clang/lib/CodeGen/CGVTT.cpp b/clang/lib/CodeGen/CGVTT.cpp
index 78928d04220..85e5298eebe 100644
--- a/clang/lib/CodeGen/CGVTT.cpp
+++ b/clang/lib/CodeGen/CGVTT.cpp
@@ -100,7 +100,7 @@ CodeGenVTables::EmitVTTDefinition(llvm::GlobalVariable *VTT,
     VTT->setComdat(CGM.getModule().getOrInsertComdat(VTT->getName()));
 
   // Set the right visibility.
-  CGM.setGlobalVisibility(VTT, RD, ForDefinition);
+  CGM.setGVProperties(VTT, RD, ForDefinition);
 }
 
 llvm::GlobalVariable *CodeGenVTables::GetAddrOfVTT(const CXXRecordDecl *RD) {
diff --git a/clang/lib/CodeGen/CGVTables.cpp b/clang/lib/CodeGen/CGVTables.cpp
index 2d9bf3bce92..a3336d90f42 100644
--- a/clang/lib/CodeGen/CGVTables.cpp
+++ b/clang/lib/CodeGen/CGVTables.cpp
@@ -51,7 +51,7 @@ llvm::Constant *CodeGenModule::GetAddrOfThunk(GlobalDecl GD,
 
 static void setThunkVisibility(CodeGenModule &CGM, const CXXMethodDecl *MD,
                                const ThunkInfo &Thunk, llvm::Function *Fn) {
-  CGM.setGlobalVisibility(Fn, MD, ForDefinition);
+  CGM.setGVProperties(Fn, MD, ForDefinition);
 }
 
 static void setThunkProperties(CodeGenModule &CGM, const ThunkInfo &Thunk,
@@ -730,7 +730,7 @@ CodeGenVTables::GenerateConstructionVTable(const CXXRecordDecl *RD,
   // Create the variable that will hold the construction vtable.
   llvm::GlobalVariable *VTable =
     CGM.CreateOrReplaceCXXRuntimeVariable(Name, VTType, Linkage);
-  CGM.setGlobalVisibility(VTable, RD, ForDefinition);
+  CGM.setGVProperties(VTable, RD, ForDefinition);
 
   // V-tables are always unnamed_addr.
   VTable->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 760327deb17..12af14b77d3 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -717,6 +717,63 @@ void CodeGenModule::setGlobalVisibility(llvm::GlobalValue *GV,
     GV->setVisibility(GetLLVMVisibility(LV.getVisibility()));
 }
 
+static bool shouldAssumeDSOLocal(const CodeGenModule &CGM,
+                                 llvm::GlobalValue *GV, const NamedDecl *D,
+                                 ForDefinition_t IsForDefinition) {
+  const llvm::Triple &TT = CGM.getTriple();
+  // Only handle ELF for now.
+  if (!TT.isOSBinFormatELF())
+    return false;
+
+  // If this is not an executable, don't assume anything is local.
+  const auto &CGOpts = CGM.getCodeGenOpts();
+  llvm::Reloc::Model RM = CGOpts.RelocationModel;
+  const auto &LOpts = CGM.getLangOpts();
+  if (RM != llvm::Reloc::Static && !LOpts.PIE)
+    return false;
+
+  // A definition cannot be preempted from an executable.
+  if (IsForDefinition)
+    return true;
+
+  // Most PIC code sequences that assume that a symbol is local cannot produce a
+  // 0 if it turns out the symbol is undefined. While this is ABI and relocation
+  // depended, it seems worth it to handle it here.
+  if (RM == llvm::Reloc::PIC_ && GV->hasExternalWeakLinkage())
+    return false;
+
+  // PPC has no copy relocations and cannot use a plt entry as a symbol address.
+  llvm::Triple::ArchType Arch = TT.getArch();
+  if (Arch == llvm::Triple::ppc || Arch == llvm::Triple::ppc64 ||
+      Arch == llvm::Triple::ppc64le)
+    return false;
+
+  // If we can use copy relocations we can assume it is local.
+  if (isa<VarDecl>(D) &&
+      (RM == llvm::Reloc::Static || CGOpts.PIECopyRelocations))
+    return true;
+
+  // If we can use a plt entry as the symbol address we can assume it
+  // is local.
+  if (isa<FunctionDecl>(D) && !CGOpts.NoPLT)
+    return true;
+
+  // Otherwise don't assue it is local.
+  return false;
+}
+
+void CodeGenModule::setDSOLocal(llvm::GlobalValue *GV, const NamedDecl *D,
+                                ForDefinition_t IsForDefinition) const {
+  if (shouldAssumeDSOLocal(*this, GV, D, IsForDefinition))
+    GV->setDSOLocal(true);
+}
+
+void CodeGenModule::setGVProperties(llvm::GlobalValue *GV, const NamedDecl *D,
+                                    ForDefinition_t IsForDefinition) const {
+  setGlobalVisibility(GV, D, IsForDefinition);
+  setDSOLocal(GV, D, IsForDefinition);
+}
+
 static llvm::GlobalVariable::ThreadLocalMode GetLLVMTLSModel(StringRef S) {
   return llvm::StringSwitch<llvm::GlobalVariable::ThreadLocalMode>(S)
       .Case("global-dynamic", llvm::GlobalVariable::GeneralDynamicTLSModel)
@@ -1174,7 +1231,7 @@ void CodeGenModule::SetLLVMFunctionAttributesForDefinition(const Decl *D,
 void CodeGenModule::SetCommonAttributes(const Decl *D,
                                         llvm::GlobalValue *GV) {
   if (const auto *ND = dyn_cast_or_null<NamedDecl>(D))
-    setGlobalVisibility(GV, ND, ForDefinition);
+    setGVProperties(GV, ND, ForDefinition);
   else
     GV->setVisibility(llvm::GlobalValue::DefaultVisibility);
 
@@ -1316,7 +1373,7 @@ void CodeGenModule::SetFunctionAttributes(GlobalDecl GD, llvm::Function *F,
   // overridden by a definition.
 
   setLinkageForGV(F, FD);
-  setGlobalVisibility(F, FD, NotForDefinition);
+  setGVProperties(F, FD, NotForDefinition);
 
   if (FD->getAttr<PragmaClangTextSectionAttr>()) {
     F->addFnAttr("implicit-section-name");
@@ -2638,7 +2695,7 @@ CodeGenModule::GetOrCreateLLVMGlobal(StringRef MangledName,
     GV->setAlignment(getContext().getDeclAlign(D).getQuantity());
 
     setLinkageForGV(GV, D);
-    setGlobalVisibility(GV, D, NotForDefinition);
+    setGVProperties(GV, D, NotForDefinition);
 
     if (D->getTLSKind()) {
       if (D->getTLSKind() == VarDecl::TLS_Dynamic)
@@ -3457,7 +3514,7 @@ void CodeGenModule::EmitGlobalFunctionDefinition(GlobalDecl GD,
   setFunctionDLLStorageClass(GD, Fn);
 
   // FIXME: this is redundant with part of setFunctionDefinitionAttributes
-  setGlobalVisibility(Fn, D, ForDefinition);
+  setGVProperties(Fn, D, ForDefinition);
 
   MaybeHandleStaticInExternC(D, Fn);
 
@@ -4053,7 +4110,7 @@ ConstantAddress CodeGenModule::GetAddrOfGlobalTemporary(
       getModule(), Type, Constant, Linkage, InitialValue, Name.c_str(),
       /*InsertBefore=*/nullptr, llvm::GlobalVariable::NotThreadLocal, TargetAS);
   if (emitter) emitter->finalize(GV);
-  setGlobalVisibility(GV, VD, ForDefinition);
+  setGVProperties(GV, VD, ForDefinition);
   GV->setAlignment(Align.getQuantity());
   if (supportsCOMDAT() && GV->isWeakForLinker())
     GV->setComdat(TheModule.getOrInsertComdat(GV->getName()));
diff --git a/clang/lib/CodeGen/CodeGenModule.h b/clang/lib/CodeGen/CodeGenModule.h
index 42e9e1be316..3ae041e8d5e 100644
--- a/clang/lib/CodeGen/CodeGenModule.h
+++ b/clang/lib/CodeGen/CodeGenModule.h
@@ -722,6 +722,12 @@ public:
   void setGlobalVisibility(llvm::GlobalValue *GV, const NamedDecl *D,
                            ForDefinition_t IsForDefinition) const;
 
+  void setDSOLocal(llvm::GlobalValue *GV, const NamedDecl *D,
+                   ForDefinition_t IsForDefinition) const;
+
+  void setGVProperties(llvm::GlobalValue *GV, const NamedDecl *D,
+                       ForDefinition_t IsForDefinition) const;
+
   /// Set the TLS mode for the given LLVM GlobalValue for the thread-local
   /// variable declaration D.
   void setTLSMode(llvm::GlobalValue *GV, const VarDecl &D) const;
diff --git a/clang/lib/CodeGen/ItaniumCXXABI.cpp b/clang/lib/CodeGen/ItaniumCXXABI.cpp
index 8fd0839487d..3ccdf85fa0d 100644
--- a/clang/lib/CodeGen/ItaniumCXXABI.cpp
+++ b/clang/lib/CodeGen/ItaniumCXXABI.cpp
@@ -1531,7 +1531,7 @@ void ItaniumCXXABI::emitVTableDefinitions(CodeGenVTables &CGVT,
     VTable->setComdat(CGM.getModule().getOrInsertComdat(VTable->getName()));
 
   // Set the right visibility.
-  CGM.setGlobalVisibility(VTable, RD, ForDefinition);
+  CGM.setGVProperties(VTable, RD, ForDefinition);
 
   // Use pointer alignment for the vtable. Otherwise we would align them based
   // on the size of the initializer which doesn't make sense as only single
@@ -1641,7 +1641,7 @@ llvm::GlobalVariable *ItaniumCXXABI::getAddrOfVTable(const CXXRecordDecl *RD,
   VTable = CGM.CreateOrReplaceCXXRuntimeVariable(
       Name, VTableType, llvm::GlobalValue::ExternalLinkage);
   VTable->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
-  CGM.setGlobalVisibility(VTable, RD, NotForDefinition);
+  CGM.setGVProperties(VTable, RD, NotForDefinition);
 
   if (RD->hasAttr<DLLImportAttr>())
     VTable->setDLLStorageClass(llvm::GlobalValue::DLLImportStorageClass);
@@ -2052,6 +2052,7 @@ void ItaniumCXXABI::EmitGuardedInit(CodeGenFunction &CGF,
                                      false, var->getLinkage(),
                                      llvm::ConstantInt::get(guardTy, 0),
                                      guardName.str());
+    guard->setDSOLocal(var->isDSOLocal());
     guard->setVisibility(var->getVisibility());
     // If the variable is thread-local, so is its guard variable.
     guard->setThreadLocalMode(var->getThreadLocalMode());
@@ -3212,7 +3213,10 @@ llvm::Constant *ItaniumRTTIBuilder::BuildTypeInfo(QualType Ty, bool Force,
     llvmVisibility = CodeGenModule::GetLLVMVisibility(Ty->getVisibility());
 
   TypeName->setVisibility(llvmVisibility);
+  CGM.setDSOLocal(TypeName, Ty->getAsCXXRecordDecl(), ForDefinition);
+
   GV->setVisibility(llvmVisibility);
+  CGM.setDSOLocal(GV, Ty->getAsCXXRecordDecl(), ForDefinition);
 
   if (CGM.getTriple().isWindowsItaniumEnvironment()) {
     auto RD = Ty->getAsCXXRecordDecl();