diff --git a/llvm/lib/CodeGen/GlobalISel/InstructionSelector.cpp b/llvm/lib/CodeGen/GlobalISel/InstructionSelector.cpp
--- a/llvm/lib/CodeGen/GlobalISel/InstructionSelector.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/InstructionSelector.cpp
@@ -41,8 +41,12 @@
   MachineFunction &MF = *MBB.getParent();
   MachineRegisterInfo &MRI = MF.getRegInfo();
 
-  return constrainOperandRegClass(MF, TRI, MRI, TII, RBI, I, RC,
-                                  I.getOperand(OpIdx));
+  MachineOperand &MO = I.getOperand(OpIdx);
+  Register NewReg = constrainOperandRegClass(MF, TRI, MRI, TII, RBI, I, RC, MO);
+  if (NewReg != MO.getReg()) {
+    MO.setReg(NewReg);
+  }
+  return true;
 }
 
 bool InstructionSelector::isOperandImmEqual(