diff --git a/llvm/include/llvm/CodeGen/GlobalISel/MachineIRBuilder.h b/llvm/include/llvm/CodeGen/GlobalISel/MachineIRBuilder.h
--- a/llvm/include/llvm/CodeGen/GlobalISel/MachineIRBuilder.h
+++ b/llvm/include/llvm/CodeGen/GlobalISel/MachineIRBuilder.h
@@ -122,14 +122,22 @@
     MachineInstrBuilder SrcMIB;
     Register Reg;
     CmpInst::Predicate Pred;
+    int64_t Imm;
   };
 
 public:
-  enum class SrcType { Ty_Reg, Ty_MIB, Ty_Predicate };
+  enum class SrcType { Ty_Reg, Ty_MIB, Ty_Predicate, Ty_Imm };
   SrcOp(Register R) : Reg(R), Ty(SrcType::Ty_Reg) {}
   SrcOp(const MachineOperand &Op) : Reg(Op.getReg()), Ty(SrcType::Ty_Reg) {}
   SrcOp(const MachineInstrBuilder &MIB) : SrcMIB(MIB), Ty(SrcType::Ty_MIB) {}
   SrcOp(const CmpInst::Predicate P) : Pred(P), Ty(SrcType::Ty_Predicate) {}
+  /// Use of registers held in unsigned integer variables (or more rarely signed
+  /// integers) is no longer permitted to avoid ambiguity with upcoming support
+  /// for immediates.
+  SrcOp(unsigned) = delete;
+  SrcOp(int) = delete;
+  SrcOp(uint64_t V) : Imm(V), Ty(SrcType::Ty_Imm) {}
+  SrcOp(int64_t V) : Imm(V), Ty(SrcType::Ty_Imm) {}
 
   void addSrcToMIB(MachineInstrBuilder &MIB) const {
     switch (Ty) {
@@ -142,12 +150,16 @@
     case SrcType::Ty_MIB:
       MIB.addUse(SrcMIB->getOperand(0).getReg());
       break;
+    case SrcType::Ty_Imm:
+      MIB.addImm(Imm);
+      break;
     }
   }
 
   LLT getLLTTy(const MachineRegisterInfo &MRI) const {
     switch (Ty) {
     case SrcType::Ty_Predicate:
+    case SrcType::Ty_Imm:
       llvm_unreachable("Not a register operand");
     case SrcType::Ty_Reg:
       return MRI.getType(Reg);
@@ -160,6 +172,7 @@
   Register getReg() const {
     switch (Ty) {
     case SrcType::Ty_Predicate:
+    case SrcType::Ty_Imm:
       llvm_unreachable("Not a register operand");
     case SrcType::Ty_Reg:
       return Reg;
@@ -178,6 +191,15 @@
     }
   }
 
+  int64_t getImm() const {
+    switch (Ty) {
+    case SrcType::Ty_Imm:
+      return Imm;
+    default:
+      llvm_unreachable("Not an immediate");
+    }
+  }
+
   SrcType getSrcOpKind() const { return Ty; }
 
 private:
diff --git a/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp b/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
--- a/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
+++ b/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
@@ -544,7 +544,7 @@
 /// SubRegCopy (To class) = COPY CopyReg:SubReg
 /// Dst = COPY SubRegCopy
 static bool selectSubregisterCopy(MachineInstr &I, MachineRegisterInfo &MRI,
-                                  const RegisterBankInfo &RBI, unsigned SrcReg,
+                                  const RegisterBankInfo &RBI, Register SrcReg,
                                   const TargetRegisterClass *From,
                                   const TargetRegisterClass *To,
                                   unsigned SubReg) {
diff --git a/llvm/lib/Target/AArch64/AArch64LegalizerInfo.cpp b/llvm/lib/Target/AArch64/AArch64LegalizerInfo.cpp
--- a/llvm/lib/Target/AArch64/AArch64LegalizerInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64LegalizerInfo.cpp
@@ -689,7 +689,7 @@
   // legalized. In order to allow further legalization of the inst, we create
   // a new instruction and erase the existing one.
 
-  unsigned ValReg = MI.getOperand(0).getReg();
+  Register ValReg = MI.getOperand(0).getReg();
   const LLT ValTy = MRI.getType(ValReg);
 
   if (!ValTy.isVector() || !ValTy.getElementType().isPointer() ||