Auto-sandboxing: Switch to automatic scratch register invalidation

include/llvm/MC/MCNaClExpander.h

 //===- MCNaClExpander.h -----------------------------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file declares the MCNaClExpander class. This is an abstract
@@ skipping 16 matching lines @@
 class MCStreamer;
 
 class MCNaClExpander {
 private:
   SmallVector<unsigned, 2> ScratchRegs;
   const MCContext &Ctx;
 
 protected:
   std::unique_ptr<MCInstrInfo> InstInfo;
   std::unique_ptr<MCRegisterInfo> RegInfo;
+  void invalidateScratchRegs(const MCInst &Inst);
+  unsigned getScratchReg(int index);
+  unsigned numScratchRegs() const;
+  virtual bool isValidScratchRegister(unsigned Reg) const = 0;
 
 public:
   MCNaClExpander(const MCContext &Ctx, std::unique_ptr<MCRegisterInfo> &&RI,
                  std::unique_ptr<MCInstrInfo> &&II)
       : Ctx(Ctx), InstInfo(std::move(II)), RegInfo(std::move(RI)) {}
 
   void Error(const MCInst &Inst, const char msg[]);
 
-  void pushScratchReg(unsigned Reg);
-  unsigned popScratchReg();
-  unsigned getScratchReg(int index);
-  unsigned numScratchRegs() const;
+  bool addScratchReg(unsigned Reg);
+  void clearScratchRegs();
 
   bool isPseudo(const MCInst &Inst) const;
 
   bool mayAffectControlFlow(const MCInst &Inst) const;
   bool isCall(const MCInst &Inst) const;
   bool isBranch(const MCInst &Inst) const;
   bool isIndirectBranch(const MCInst &Inst) const;
   bool isReturn(const MCInst &Inst) const;
 
   bool mayLoad(const MCInst &Inst) const;
   bool mayStore(const MCInst &Inst) const;
 
   bool mayModifyRegister(const MCInst &Inst, unsigned Reg) const;
   bool explicitlyModifiesRegister(const MCInst &Inst, unsigned Reg) const;
 
   void replaceDefinitions(MCInst &Inst, unsigned RegOld, unsigned RegNew) const;
 
   virtual ~MCNaClExpander() = default;
   virtual bool expandInst(const MCInst &Inst, MCStreamer &Out,
                           const MCSubtargetInfo &STI) = 0;
 };
 
 }
 #endif