[NFC] Replace hard-coded usages of SystemZ::R15D with SpecialRegisters API

[Everybody0523]

Summary

This patch changes hard-coded usages of SystemZ::R15D with calls to the getStackPointerRegister function. Uses in the LowerCall function are avoided to avoid merge conflicts with an expected upcoming patch.

[uweigand]

LGTM.

llvm/lib/Target/SystemZ/SystemZISelLowering.cpp

static MachineOperand earlyUseOperand(MachineOperand Op) {
   return Op;
 }
 
 SystemZTargetLowering::SystemZTargetLowering(const TargetMachine &TM,
                                              const SystemZSubtarget &STI)
     : TargetLowering(TM), Subtarget(STI) {
   MVT PtrVT = MVT::getIntegerVT(8 * TM.getPointerSize(0));
 
+  auto *Regs = STI.getSpecialRegisters();
+
   // Set up the register classes.
   if (Subtarget.hasHighWord())
     addRegisterClass(MVT::i32, &SystemZ::GRX32BitRegClass);
   else
     addRegisterClass(MVT::i32, &SystemZ::GR32BitRegClass);
   addRegisterClass(MVT::i64, &SystemZ::GR64BitRegClass);
   if (!useSoftFloat()) {
     if (Subtarget.hasVector()) {
if (Subtarget.hasVector()) {
       addRegisterClass(MVT::v2f64, &SystemZ::VR128BitRegClass);
     }
   }
 
   // Compute derived properties from the register classes
   computeRegisterProperties(Subtarget.getRegisterInfo());
 
   // Set up special registers.
-  setStackPointerRegisterToSaveRestore(SystemZ::R15D);
+  setStackPointerRegisterToSaveRestore(Regs->getStackPointerRegister());
 
   // TODO: It may be better to default to latency-oriented scheduling, however
   // LLVM's current latency-oriented scheduler can't handle physreg definitions
   // such as SystemZ has with CC, so set this to the register-pressure
   // scheduler, because it can.
   setSchedulingPreference(Sched::RegPressure);
 
   setBooleanContents(ZeroOrOneBooleanContent);
if (auto *AI = dyn_cast<AtomicCmpXchgInst>(&I))
     if (AI->isAtomic())
       return MachineMemOperand::MOVolatile;
   return MachineMemOperand::MONone;
 }
 
 SDValue SystemZTargetLowering::lowerSTACKSAVE(SDValue Op,
                                               SelectionDAG &DAG) const {
   MachineFunction &MF = DAG.getMachineFunction();
+  const SystemZSubtarget *Subtarget = &MF.getSubtarget<SystemZSubtarget>();
+  auto *Regs = Subtarget->getSpecialRegisters();
   MF.getInfo<SystemZMachineFunctionInfo>()->setManipulatesSP(true);
   if (MF.getFunction().getCallingConv() == CallingConv::GHC)
     report_fatal_error("Variable-sized stack allocations are not supported "
                        "in GHC calling convention");
   return DAG.getCopyFromReg(Op.getOperand(0), SDLoc(Op),
-                            SystemZ::R15D, Op.getValueType());
+                            Regs->getStackPointerRegister(), Op.getValueType());
 }
 
 SDValue SystemZTargetLowering::lowerSTACKRESTORE(SDValue Op,
                                                  SelectionDAG &DAG) const {
   MachineFunction &MF = DAG.getMachineFunction();
+  const SystemZSubtarget *Subtarget = &MF.getSubtarget<SystemZSubtarget>();
+  auto *Regs = Subtarget->getSpecialRegisters();
   MF.getInfo<SystemZMachineFunctionInfo>()->setManipulatesSP(true);
   bool StoreBackchain = MF.getFunction().hasFnAttribute("backchain");
 
   if (MF.getFunction().getCallingConv() == CallingConv::GHC)
     report_fatal_error("Variable-sized stack allocations are not supported "
                        "in GHC calling convention");
 
   SDValue Chain = Op.getOperand(0);
   SDValue NewSP = Op.getOperand(1);
   SDValue Backchain;
   SDLoc DL(Op);
 
   if (StoreBackchain) {
-    SDValue OldSP = DAG.getCopyFromReg(Chain, DL, SystemZ::R15D, MVT::i64);
+    SDValue OldSP = DAG.getCopyFromReg(
+        Chain, DL, Regs->getStackPointerRegister(), MVT::i64);
     Backchain = DAG.getLoad(MVT::i64, DL, Chain, getBackchainAddress(OldSP, DAG),
                             MachinePointerInfo());
   }
 
-  Chain = DAG.getCopyToReg(Chain, DL, SystemZ::R15D, NewSP);
+  Chain = DAG.getCopyToReg(Chain, DL, Regs->getStackPointerRegister(), NewSP);
 
   if (StoreBackchain)
     Chain = DAG.getStore(Chain, DL, Backchain, getBackchainAddress(NewSP, DAG),
                          MachinePointerInfo());
 
   return Chain;
 }