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.

llvm-svn: 159077

1 files changed, 33 insertions, 7 deletions

diff --git a/llvm/lib/Target/TargetMachine.cpp b/llvm/lib/Target/TargetMachine.cpp
index 6cdab5a266a..382571982b9 100644
--- a/llvm/lib/Target/TargetMachine.cpp
+++ b/llvm/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;
 }
-