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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154294 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 6 insertions, 0 deletions

diff --git a/tools/llc/llc.cpp b/tools/llc/llc.cpp
index 191b649c05..9e30ac198b 100644
--- a/tools/llc/llc.cpp
+++ b/tools/llc/llc.cpp
@@ -263,6 +263,11 @@ TrapFuncName("trap-func", cl::Hidden,
   cl::init(""));
 
 static cl::opt<bool>
+EnablePIE("enable-pie",
+  cl::desc("Assume the creation of a position independent executable."),
+  cl::init(false));
+
+static cl::opt<bool>
 SegmentedStacks("segmented-stacks",
   cl::desc("Use segmented stacks if possible."),
   cl::init(false));
@@ -467,6 +472,7 @@ int main(int argc, char **argv) {
   Options.RealignStack = EnableRealignStack;
   Options.DisableJumpTables = DisableSwitchTables;
   Options.TrapFuncName = TrapFuncName;
+  Options.PositionIndependentExecutable = EnablePIE;
   Options.EnableSegmentedStacks = SegmentedStacks;
 
   std::auto_ptr<TargetMachine>