diff --git a/include/llvm/CodeGen/GlobalISel/InstructionSelector.h b/include/llvm/CodeGen/GlobalISel/InstructionSelector.h
index bf9991eb08d..5b8243a93e7 100644
--- a/include/llvm/CodeGen/GlobalISel/InstructionSelector.h
+++ b/include/llvm/CodeGen/GlobalISel/InstructionSelector.h
@@ -527,16 +527,6 @@ protected:
         "Subclasses must override this with a tablegen-erated function");
   }
 
-  /// Constrain a register operand of an instruction \p I to a specified
-  /// register class. This could involve inserting COPYs before (for uses) or
-  /// after (for defs) and may replace the operand of \p I.
-  /// \returns whether operand regclass constraining succeeded.
-  bool constrainOperandRegToRegClass(MachineInstr &I, unsigned OpIdx,
-                                     const TargetRegisterClass &RC,
-                                     const TargetInstrInfo &TII,
-                                     const TargetRegisterInfo &TRI,
-                                     const RegisterBankInfo &RBI) const;
-
   bool isOperandImmEqual(const MachineOperand &MO, int64_t Value,
                          const MachineRegisterInfo &MRI) const;
 
diff --git a/include/llvm/CodeGen/GlobalISel/InstructionSelectorImpl.h b/include/llvm/CodeGen/GlobalISel/InstructionSelectorImpl.h
index bcb84c337f5..82e26b0bc35 100644
--- a/include/llvm/CodeGen/GlobalISel/InstructionSelectorImpl.h
+++ b/include/llvm/CodeGen/GlobalISel/InstructionSelectorImpl.h
@@ -1058,8 +1058,12 @@ bool InstructionSelector::executeMatchTable(
       int64_t OpIdx = MatchTable[CurrentIdx++];
       int64_t RCEnum = MatchTable[CurrentIdx++];
       assert(OutMIs[InsnID] && "Attempted to add to undefined instruction");
-      constrainOperandRegToRegClass(*OutMIs[InsnID].getInstr(), OpIdx,
-                                    *TRI.getRegClass(RCEnum), TII, TRI, RBI);
+      MachineInstr &I = *OutMIs[InsnID].getInstr();
+      MachineFunction &MF = *I.getParent()->getParent();
+      MachineRegisterInfo &MRI = MF.getRegInfo();
+      const TargetRegisterClass &RC = *TRI.getRegClass(RCEnum);
+      MachineOperand &MO = I.getOperand(OpIdx);
+      constrainOperandRegClass(MF, TRI, MRI, TII, RBI, I, RC, MO);
       DEBUG_WITH_TYPE(TgtInstructionSelector::getName(),
                       dbgs() << CurrentIdx << ": GIR_ConstrainOperandRC(OutMIs["
                              << InsnID << "], " << OpIdx << ", " << RCEnum
diff --git a/include/llvm/CodeGen/GlobalISel/Utils.h b/include/llvm/CodeGen/GlobalISel/Utils.h
index 9bd5180f722..ed75cde6f31 100644
--- a/include/llvm/CodeGen/GlobalISel/Utils.h
+++ b/include/llvm/CodeGen/GlobalISel/Utils.h
@@ -52,9 +52,10 @@ Register constrainRegToClass(MachineRegisterInfo &MRI,
 
 /// Constrain the Register operand OpIdx, so that it is now constrained to the
 /// TargetRegisterClass passed as an argument (RegClass).
-/// If this fails, create a new virtual register in the correct class and
-/// insert a COPY before \p InsertPt if it is a use or after if it is a
-/// definition. The debug location of \p InsertPt is used for the new copy.
+/// If this fails, create a new virtual register in the correct class and insert
+/// a COPY before \p InsertPt if it is a use or after if it is a definition.
+/// In both cases, the function also updates the register of RegMo. The debug
+/// location of \p InsertPt is used for the new copy.
 ///
 /// \return The virtual register constrained to the right register class.
 Register constrainOperandRegClass(const MachineFunction &MF,
@@ -64,12 +65,13 @@ Register constrainOperandRegClass(const MachineFunction &MF,
                                   const RegisterBankInfo &RBI,
                                   MachineInstr &InsertPt,
                                   const TargetRegisterClass &RegClass,
-                                  const MachineOperand &RegMO);
+                                  MachineOperand &RegMO);
 
-/// Try to constrain Reg so that it is usable by argument OpIdx of the
-/// provided MCInstrDesc \p II. If this fails, create a new virtual
-/// register in the correct class and insert a COPY before \p InsertPt
-/// if it is a use or after if it is a definition.
+/// Try to constrain Reg so that it is usable by argument OpIdx of the provided
+/// MCInstrDesc \p II. If this fails, create a new virtual register in the
+/// correct class and insert a COPY before \p InsertPt if it is a use or after
+/// if it is a definition. In both cases, the function also updates the register
+/// of RegMo.
 /// This is equivalent to constrainOperandRegClass(..., RegClass, ...)
 /// with RegClass obtained from the MCInstrDesc. The debug location of \p
 /// InsertPt is used for the new copy.
@@ -81,7 +83,7 @@ Register constrainOperandRegClass(const MachineFunction &MF,
                                   const TargetInstrInfo &TII,
                                   const RegisterBankInfo &RBI,
                                   MachineInstr &InsertPt, const MCInstrDesc &II,
-                                  const MachineOperand &RegMO, unsigned OpIdx);
+                                  MachineOperand &RegMO, unsigned OpIdx);
 
 /// Mutate the newly-selected instruction \p I to constrain its (possibly
 /// generic) virtual register operands to the instruction's register class.
diff --git a/lib/CodeGen/GlobalISel/InstructionSelector.cpp b/lib/CodeGen/GlobalISel/InstructionSelector.cpp
index 3eca16808ea..4fec9e628dd 100644
--- a/lib/CodeGen/GlobalISel/InstructionSelector.cpp
+++ b/lib/CodeGen/GlobalISel/InstructionSelector.cpp
@@ -33,18 +33,6 @@ InstructionSelector::MatcherState::MatcherState(unsigned MaxRenderers)
 
 InstructionSelector::InstructionSelector() = default;
 
-bool InstructionSelector::constrainOperandRegToRegClass(
-    MachineInstr &I, unsigned OpIdx, const TargetRegisterClass &RC,
-    const TargetInstrInfo &TII, const TargetRegisterInfo &TRI,
-    const RegisterBankInfo &RBI) const {
-  MachineBasicBlock &MBB = *I.getParent();
-  MachineFunction &MF = *MBB.getParent();
-  MachineRegisterInfo &MRI = MF.getRegInfo();
-
-  return constrainOperandRegClass(MF, TRI, MRI, TII, RBI, I, RC,
-                                  I.getOperand(OpIdx));
-}
-
 bool InstructionSelector::isOperandImmEqual(
     const MachineOperand &MO, int64_t Value,
     const MachineRegisterInfo &MRI) const {
diff --git a/lib/CodeGen/GlobalISel/Utils.cpp b/lib/CodeGen/GlobalISel/Utils.cpp
index aeacd4fb797..868385c2def 100644
--- a/lib/CodeGen/GlobalISel/Utils.cpp
+++ b/lib/CodeGen/GlobalISel/Utils.cpp
@@ -48,7 +48,7 @@ Register llvm::constrainOperandRegClass(
     const MachineFunction &MF, const TargetRegisterInfo &TRI,
     MachineRegisterInfo &MRI, const TargetInstrInfo &TII,
     const RegisterBankInfo &RBI, MachineInstr &InsertPt,
-    const TargetRegisterClass &RegClass, const MachineOperand &RegMO) {
+    const TargetRegisterClass &RegClass, MachineOperand &RegMO) {
   Register Reg = RegMO.getReg();
   // Assume physical registers are properly constrained.
   assert(Register::isVirtualRegister(Reg) && "PhysReg not implemented");
@@ -69,6 +69,13 @@ Register llvm::constrainOperandRegClass(
               TII.get(TargetOpcode::COPY), Reg)
           .addReg(ConstrainedReg);
     }
+    if (GISelChangeObserver *Observer = MF.getObserver()) {
+      Observer->changingInstr(*RegMO.getParent());
+    }
+    RegMO.setReg(ConstrainedReg);
+    if (GISelChangeObserver *Observer = MF.getObserver()) {
+      Observer->changedInstr(*RegMO.getParent());
+    }
   } else {
     if (GISelChangeObserver *Observer = MF.getObserver()) {
       if (!RegMO.isDef()) {
@@ -86,7 +93,7 @@ Register llvm::constrainOperandRegClass(
     const MachineFunction &MF, const TargetRegisterInfo &TRI,
     MachineRegisterInfo &MRI, const TargetInstrInfo &TII,
     const RegisterBankInfo &RBI, MachineInstr &InsertPt, const MCInstrDesc &II,
-    const MachineOperand &RegMO, unsigned OpIdx) {
+    MachineOperand &RegMO, unsigned OpIdx) {
   Register Reg = RegMO.getReg();
   // Assume physical registers are properly constrained.
   assert(Register::isVirtualRegister(Reg) && "PhysReg not implemented");
@@ -156,8 +163,7 @@ bool llvm::constrainSelectedInstRegOperands(MachineInstr &I,
     // If the operand is a vreg, we should constrain its regclass, and only
     // insert COPYs if that's impossible.
     // constrainOperandRegClass does that for us.
-    MO.setReg(constrainOperandRegClass(MF, TRI, MRI, TII, RBI, I, I.getDesc(),
-                                       MO, OpI));
+    constrainOperandRegClass(MF, TRI, MRI, TII, RBI, I, I.getDesc(), MO, OpI);
 
     // Tie uses to defs as indicated in MCInstrDesc if this hasn't already been
     // done.
diff --git a/lib/Target/AArch64/GISel/AArch64CallLowering.cpp b/lib/Target/AArch64/GISel/AArch64CallLowering.cpp
index c6be2007d61..cb81377b767 100644
--- a/lib/Target/AArch64/GISel/AArch64CallLowering.cpp
+++ b/lib/Target/AArch64/GISel/AArch64CallLowering.cpp
@@ -933,10 +933,9 @@ bool AArch64CallLowering::lowerTailCall(
   // If Callee is a reg, since it is used by a target specific instruction,
   // it must have a register class matching the constraint of that instruction.
   if (Info.Callee.isReg())
-    MIB->getOperand(0).setReg(constrainOperandRegClass(
-        MF, *TRI, MRI, *MF.getSubtarget().getInstrInfo(),
-        *MF.getSubtarget().getRegBankInfo(), *MIB, MIB->getDesc(), Info.Callee,
-        0));
+    constrainOperandRegClass(MF, *TRI, MRI, *MF.getSubtarget().getInstrInfo(),
+                             *MF.getSubtarget().getRegBankInfo(), *MIB,
+                             MIB->getDesc(), Info.Callee, 0);
 
   MF.getFrameInfo().setHasTailCall();
   Info.LoweredTailCall = true;
@@ -1018,10 +1017,9 @@ bool AArch64CallLowering::lowerCall(MachineIRBuilder &MIRBuilder,
   // instruction, it must have a register class matching the
   // constraint of that instruction.
   if (Info.Callee.isReg())
-    MIB->getOperand(0).setReg(constrainOperandRegClass(
-        MF, *TRI, MRI, *MF.getSubtarget().getInstrInfo(),
-        *MF.getSubtarget().getRegBankInfo(), *MIB, MIB->getDesc(), Info.Callee,
-        0));
+    constrainOperandRegClass(MF, *TRI, MRI, *MF.getSubtarget().getInstrInfo(),
+                             *MF.getSubtarget().getRegBankInfo(), *MIB,
+                             MIB->getDesc(), Info.Callee, 0);
 
   // Finally we can copy the returned value back into its virtual-register. In
   // symmetry with the arguments, the physical register must be an