Teach LLVM about a PIE option which, when enabled on top of PIC, makes

optimizations which are valid for position independent code being linked
into a single executable, but not for such code being linked into
a shared library.

I discussed the design of this with Eric Christopher, and the decision
was to support an optional bit rather than a completely separate
relocation model. Fundamentally, this is still PIC relocation, its just
that certain optimizations are only valid under a PIC relocation model
when the resulting code won't be in a shared library. The simplest path
to here is to expose a single bit option in the TargetOptions. If folks
have different/better designs, I'm all ears. =]

I've included the first optimization based upon this: changing TLS
models to the *Exec models when PIE is enabled. This is the LLVM
component of PR12380 and is all of the hard work.

llvm-svn: 154294

1 files changed, 2 insertions, 1 deletions

diff --git a/llvm/lib/Target/TargetMachine.cpp b/llvm/lib/Target/TargetMachine.cpp
index b8e7f15d092..b9b2526876f 100644
--- a/llvm/lib/Target/TargetMachine.cpp
+++ b/llvm/lib/Target/TargetMachine.cpp
@@ -82,7 +82,8 @@ TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
   // For variables, is internal different from hidden?
   bool isHidden = GV->hasHiddenVisibility();
 
-  if (getRelocationModel() == Reloc::PIC_) {
+  if (getRelocationModel() == Reloc::PIC_ &&
+      !Options.PositionIndependentExecutable) {
     if (isLocal || isHidden)
       return TLSModel::LocalDynamic;
     else