[NFC][GlobalISel]: Add a convenience method to MachineInstrBuilder to simplify getOperand(i).getReg()

https://reviews.llvm.org/D57608

It's a common pattern in GISel to have a MachineInstrBuilder from which we get various regs
(commonly MIB->getOperand(0).getReg()). This adds a helper method and the above can be
replaced with MIB.getReg(0).

llvm-svn: 353223

llvm/include/llvm/CodeGen/MachineInstrBuilder.h

@@ -79,6 +79,11 @@ public:
   /// explicitly.
   MachineInstr *getInstr() const { return MI; }
 
+  /// Get the register for the operand index.
+  /// The operand at the index should be a register (asserted by
+  /// MachineOperand).
+  unsigned getReg(unsigned Idx) { return MI->getOperand(Idx).getReg(); }
+
   /// Add a new virtual register operand.
   const MachineInstrBuilder &addReg(unsigned RegNo, unsigned flags = 0,
                                     unsigned SubReg = 0) const {

llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp

@@ -840,7 +840,7 @@ void AArch64InstructionSelector::materializeLargeCMVal(
     constrainSelectedInstRegOperands(*MovI, TII, TRI, RBI);
     return DstReg;
   };
-  unsigned DstReg = BuildMovK(MovZ->getOperand(0).getReg(),
+  unsigned DstReg = BuildMovK(MovZ.getReg(0),
                               AArch64II::MO_G1 | AArch64II::MO_NC, 16, 0);
   DstReg = BuildMovK(DstReg, AArch64II::MO_G2 | AArch64II::MO_NC, 32, 0);
   BuildMovK(DstReg, AArch64II::MO_G3, 48, I.getOperand(0).getReg());

llvm/lib/Target/AArch64/AArch64LegalizerInfo.cpp

@@ -499,7 +499,7 @@ bool AArch64LegalizerInfo::legalizeVaArg(MachineInstr &MI,
     auto AlignMinus1 = MIRBuilder.buildConstant(IntPtrTy, Align - 1);
 
     unsigned ListTmp = MRI.createGenericVirtualRegister(PtrTy);
-    MIRBuilder.buildGEP(ListTmp, List, AlignMinus1->getOperand(0).getReg());
+    MIRBuilder.buildGEP(ListTmp, List, AlignMinus1.getReg(0));
 
     DstPtr = MRI.createGenericVirtualRegister(PtrTy);
     MIRBuilder.buildPtrMask(DstPtr, ListTmp, Log2_64(Align));