diff --git a/llvm/include/llvm/CodeGen/GlobalISel/Utils.h b/llvm/include/llvm/CodeGen/GlobalISel/Utils.h
--- a/llvm/include/llvm/CodeGen/GlobalISel/Utils.h
+++ b/llvm/include/llvm/CodeGen/GlobalISel/Utils.h
@@ -144,6 +144,13 @@
 MachineInstr *getDefIgnoringCopies(Register Reg,
                                    const MachineRegisterInfo &MRI);
 
+/// Find the source register for \p Reg, folding away any trivial copies. It
+/// will be an output register of the instruction that getDefIgnoringCopies
+/// returns. May return an invalid register if \p Reg is not a generic virtual
+/// register.
+Register getSrcRegIgnoringCopies(Register Reg,
+                                 const MachineRegisterInfo &MRI);
+
 /// Returns an APFloat from Val converted to the appropriate size.
 APFloat getAPFloatFromSize(double Val, unsigned Size);
 
diff --git a/llvm/lib/CodeGen/GlobalISel/Utils.cpp b/llvm/lib/CodeGen/GlobalISel/Utils.cpp
--- a/llvm/lib/CodeGen/GlobalISel/Utils.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/Utils.cpp
@@ -300,20 +300,33 @@
   return MI->getOperand(1).getFPImm();
 }
 
-llvm::MachineInstr *llvm::getDefIgnoringCopies(Register Reg,
-                                               const MachineRegisterInfo &MRI) {
+static std::pair<llvm::MachineInstr *, Register> getDefSrcRegIgnoringCopies(
+    Register Reg,
+    const MachineRegisterInfo &MRI) {
+  Register DefSrcReg = Reg;
   auto *DefMI = MRI.getVRegDef(Reg);
   auto DstTy = MRI.getType(DefMI->getOperand(0).getReg());
   if (!DstTy.isValid())
-    return nullptr;
+    return std::pair<llvm::MachineInstr *, Register>(nullptr, Register());
   while (DefMI->getOpcode() == TargetOpcode::COPY) {
     Register SrcReg = DefMI->getOperand(1).getReg();
     auto SrcTy = MRI.getType(SrcReg);
     if (!SrcTy.isValid() || SrcTy != DstTy)
       break;
     DefMI = MRI.getVRegDef(SrcReg);
+    DefSrcReg = SrcReg;
   }
-  return DefMI;
+  return std::make_pair(DefMI, DefSrcReg);
+}
+
+Register llvm::getSrcRegIgnoringCopies(Register Reg,
+                                       const MachineRegisterInfo &MRI) {
+  return getDefSrcRegIgnoringCopies(Reg, MRI).second;
+}
+
+llvm::MachineInstr *llvm::getDefIgnoringCopies(Register Reg,
+                                               const MachineRegisterInfo &MRI) {
+  return getDefSrcRegIgnoringCopies(Reg, MRI).first;
 }
 
 llvm::MachineInstr *llvm::getOpcodeDef(unsigned Opcode, Register Reg,
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
@@ -1575,10 +1575,9 @@
   // G_STORE %x:gpr(s32)
   //
   // And then continue the selection process normally.
-  MachineInstr *Def = getDefIgnoringCopies(I.getOperand(0).getReg(), MRI);
-  if (!Def)
+  Register DefDstReg = getSrcRegIgnoringCopies(I.getOperand(0).getReg(), MRI);
+  if (!DefDstReg.isValid())
     return false;
-  Register DefDstReg = Def->getOperand(0).getReg();
   LLT DefDstTy = MRI.getType(DefDstReg);
   Register StoreSrcReg = I.getOperand(0).getReg();
   LLT StoreSrcTy = MRI.getType(StoreSrcReg);