Auto-sandboxing: Switch to automatic scratch register invalidation

lib/Target/ARM/MCTargetDesc/ARMMCNaClExpander.cpp

 //===- ARMMCNaClExpander.cpp ------------------------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements the ARMMCNaClExpander class, the ARM specific
@@ skipping 10 matching lines @@
 #include "llvm/MC/MCNaClExpander.h"
 #include "llvm/MC/MCObjectFileInfo.h"
 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/MC/MCStreamer.h"
 
 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) {
   MCInst Bic;
   const int32_t EncodedMask = ARM_AM::getSOImmVal(Mask);
   Bic.setOpcode(ARM::BICri);
   Bic.addOperand(MCOperand::CreateReg(Reg));
   Bic.addOperand(MCOperand::CreateReg(Reg));
   Bic.addOperand(MCOperand::CreateImm(EncodedMask));
   Bic.addOperand(MCOperand::CreateImm(Pred));
@@ skipping 154 matching lines @@
                                         const MCSubtargetInfo &STI) {
   if (Guard)
     return false;
   Guard = true;
 
   doExpandInst(Inst, Out, STI);
 
   Guard = false;
   return true;
 }