Extend the IL for selecting TLS models (PR9788)

This allows the user/front-end to specify a model that is better
than what LLVM would choose by default. For example, a variable
might be declared as

  @x = thread_local(initialexec) global i32 42

if it will not be used in a shared library that is dlopen'ed.

If the specified model isn't supported by the target, or if LLVM can
make a better choice, a different model may be used.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159077 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 57 insertions, 8 deletions

diff --git a/lib/Target/CppBackend/CPPBackend.cpp b/lib/Target/CppBackend/CPPBackend.cpp
index cd2ebcb508..0ea2a299dd 100644
--- a/lib/Target/CppBackend/CPPBackend.cpp
+++ b/lib/Target/CppBackend/CPPBackend.cpp
@@ -130,6 +130,7 @@ namespace {
   private:
     void printLinkageType(GlobalValue::LinkageTypes LT);
     void printVisibilityType(GlobalValue::VisibilityTypes VisTypes);
+    void printThreadLocalMode(GlobalVariable::ThreadLocalMode TLM);
     void printCallingConv(CallingConv::ID cc);
     void printEscapedString(const std::string& str);
     void printCFP(const ConstantFP* CFP);
@@ -325,6 +326,26 @@ void CppWriter::printVisibilityType(GlobalValue::VisibilityTypes VisType) {
   }
 }
 
+void CppWriter::printThreadLocalMode(GlobalVariable::ThreadLocalMode TLM) {
+  switch (TLM) {
+    case GlobalVariable::NotThreadLocal:
+      Out << "GlobalVariable::NotThreadLocal";
+      break;
+    case GlobalVariable::GeneralDynamicTLSModel:
+      Out << "GlobalVariable::GeneralDynamicTLSModel";
+      break;
+    case GlobalVariable::LocalDynamicTLSModel:
+      Out << "GlobalVariable::LocalDynamicTLSModel";
+      break;
+    case GlobalVariable::InitialExecTLSModel:
+      Out << "GlobalVariable::InitialExecTLSModel";
+      break;
+    case GlobalVariable::LocalExecTLSModel:
+      Out << "GlobalVariable::LocalExecTLSModel";
+      break;
+  }
+}
+
 // printEscapedString - Print each character of the specified string, escaping
 // it if it is not printable or if it is an escape char.
 void CppWriter::printEscapedString(const std::string &Str) {
@@ -996,7 +1017,9 @@ void CppWriter::printVariableHead(const GlobalVariable *GV) {
   }
   if (GV->isThreadLocal()) {
     printCppName(GV);
-    Out << "->setThreadLocal(true);";
+    Out << "->setThreadLocalMode(";
+    printThreadLocalMode(GV->getThreadLocalMode());
+    Out << ");";
     nl(Out);
   }
   if (is_inline) {
diff --git a/lib/Target/TargetMachine.cpp b/lib/Target/TargetMachine.cpp
index 6cdab5a266..382571982b 100644
--- a/lib/Target/TargetMachine.cpp
+++ b/lib/Target/TargetMachine.cpp
@@ -77,6 +77,24 @@ CodeModel::Model TargetMachine::getCodeModel() const {
   return CodeGenInfo->getCodeModel();
 }
 
+/// Get the IR-specified TLS model for Var.
+static TLSModel::Model getSelectedTLSModel(const GlobalVariable *Var) {
+  switch (Var->getThreadLocalMode()) {
+  case GlobalVariable::NotThreadLocal:
+    llvm_unreachable("getSelectedTLSModel for non-TLS variable");
+    break;
+  case GlobalVariable::GeneralDynamicTLSModel:
+    return TLSModel::GeneralDynamic;
+  case GlobalVariable::LocalDynamicTLSModel:
+    return TLSModel::LocalDynamic;
+  case GlobalVariable::InitialExecTLSModel:
+    return TLSModel::InitialExec;
+  case GlobalVariable::LocalExecTLSModel:
+    return TLSModel::LocalExec;
+  }
+  llvm_unreachable("invalid TLS model");
+}
+
 TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
   // If GV is an alias then use the aliasee for determining
   // thread-localness.
@@ -86,22 +104,31 @@ TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
 
   bool isLocal = Var->hasLocalLinkage();
   bool isDeclaration = Var->isDeclaration();
+  bool isPIC = getRelocationModel() == Reloc::PIC_;
+  bool isPIE = Options.PositionIndependentExecutable;
   // FIXME: what should we do for protected and internal visibility?
   // For variables, is internal different from hidden?
   bool isHidden = Var->hasHiddenVisibility();
 
-  if (getRelocationModel() == Reloc::PIC_ &&
-      !Options.PositionIndependentExecutable) {
+  TLSModel::Model Model;
+  if (isPIC && !isPIE) {
     if (isLocal || isHidden)
-      return TLSModel::LocalDynamic;
+      Model = TLSModel::LocalDynamic;
     else
-      return TLSModel::GeneralDynamic;
+      Model = TLSModel::GeneralDynamic;
   } else {
     if (!isDeclaration || isHidden)
-      return TLSModel::LocalExec;
+      Model = TLSModel::LocalExec;
     else
-      return TLSModel::InitialExec;
+      Model = TLSModel::InitialExec;
   }
+
+  // If the user specified a more specific model, use that.
+  TLSModel::Model SelectedModel = getSelectedTLSModel(Var);
+  if (SelectedModel > Model)
+    return SelectedModel;
+
+  return Model;
 }
 
 /// getOptLevel - Returns the optimization level: None, Less,
@@ -135,4 +162,3 @@ void TargetMachine::setFunctionSections(bool V) {
 void TargetMachine::setDataSections(bool V) {
   DataSections = V;
 }
-