Auto-sandboxing: Switch to automatic scratch register invalidation

lib/Target/ARM/MCTargetDesc/ARMMCNaClExpander.cpp

Index: lib/Target/ARM/MCTargetDesc/ARMMCNaClExpander.cpp
diff --git a/lib/Target/ARM/MCTargetDesc/ARMMCNaClExpander.cpp b/lib/Target/ARM/MCTargetDesc/ARMMCNaClExpander.cpp
index d158064bee76529dda0442fd2be97bed622d9a93..c68cf5fb9bb9d2c023e15397a561c31ab2348b2a 100644
--- a/lib/Target/ARM/MCTargetDesc/ARMMCNaClExpander.cpp
+++ b/lib/Target/ARM/MCTargetDesc/ARMMCNaClExpander.cpp
@@ -28,6 +28,11 @@ using namespace llvm;
 const unsigned kBranchTargetMask = 0xC000000F;
 const unsigned kSandboxMask = 0xC0000000;
 
+bool ARM::ARMMCNaClExpander::isValidScratchRegister(unsigned Reg) const {
+  // TODO(dschuff): Also check the regster class.
+  return Reg != ARM::PC && Reg != ARM::SP;
+}
+
 static void emitBicMask(unsigned Mask, unsigned Reg, ARMCC::CondCodes Pred,
                         unsigned PredReg, MCStreamer &Out,
                         const MCSubtargetInfo &STI) {