[SystemZ] [NFC] Replace SpecialRegisters field with a unique_ptr instead of a raw pointer.

[Everybody0523]

Summary

This patch replaces the SpecialRegisters field with a unique_ptr instead of a raw pointer. This is better practice, and allows us to remove the definition of the dtor for the SystemZSubtarget class.

[Kai]

LGTM. Thanks for the cleanup!

[uweigand]

LGTM

llvm/lib/Target/SystemZ/SystemZSubtarget.h

protected:
   bool HasNNPAssist;
   bool HasBEAREnhancement;
   bool HasResetDATProtection;
   bool HasProcessorActivityInstrumentation;
   bool HasSoftFloat;
 
 private:
   Triple TargetTriple;
-  SystemZCallingConventionRegisters *SpecialRegisters;
+  std::unique_ptr<SystemZCallingConventionRegisters> SpecialRegisters;
   SystemZInstrInfo InstrInfo;
   SystemZTargetLowering TLInfo;
   SystemZSelectionDAGInfo TSInfo;
   SystemZFrameLowering FrameLowering;
 
   SystemZSubtarget &initializeSubtargetDependencies(StringRef CPU,
                                                     StringRef FS);
   SystemZCallingConventionRegisters *initializeSpecialRegisters(void);
 
 public:
   SystemZSubtarget(const Triple &TT, const std::string &CPU,
                    const std::string &FS, const TargetMachine &TM);
 
-  ~SystemZSubtarget();
-
   SystemZCallingConventionRegisters *getSpecialRegisters() const {
     assert(SpecialRegisters && "Unsupported SystemZ calling convention");
-    return SpecialRegisters;
+    return SpecialRegisters.get();
   }
 
   const TargetFrameLowering *getFrameLowering() const override {
     return &FrameLowering;
   }
   const SystemZInstrInfo *getInstrInfo() const override { return &InstrInfo; }
   const SystemZRegisterInfo *getRegisterInfo() const override {
     return &InstrInfo.getRegisterInfo();

llvm/lib/Target/SystemZ/SystemZSubtarget.cpp

: SystemZGenSubtargetInfo(TT, CPU, /*TuneCPU*/ CPU, FS),
       HasDeflateConversion(false), HasVectorPackedDecimalEnhancement2(false),
       HasNNPAssist(false), HasBEAREnhancement(false),
       HasResetDATProtection(false), HasProcessorActivityInstrumentation(false),
       HasSoftFloat(false), TargetTriple(TT),
       SpecialRegisters(initializeSpecialRegisters()),
       InstrInfo(initializeSubtargetDependencies(CPU, FS)), TLInfo(TM, *this),
       TSInfo(), FrameLowering() {}
 
-SystemZSubtarget::~SystemZSubtarget() { delete getSpecialRegisters(); }
-
 bool SystemZSubtarget::enableSubRegLiveness() const {
   return UseSubRegLiveness;
 }
 
 bool SystemZSubtarget::isPC32DBLSymbol(const GlobalValue *GV,
                                        CodeModel::Model CM) const {
   // PC32DBL accesses require the low bit to be clear.
   //