diff --git a/llvm/include/llvm/CodeGen/GlobalISel/LegalizationArtifactCombiner.h b/llvm/include/llvm/CodeGen/GlobalISel/LegalizationArtifactCombiner.h
--- a/llvm/include/llvm/CodeGen/GlobalISel/LegalizationArtifactCombiner.h
+++ b/llvm/include/llvm/CodeGen/GlobalISel/LegalizationArtifactCombiner.h
@@ -396,7 +396,15 @@
 
       for (unsigned Idx = 0; Idx < NumDefs; ++Idx) {
         Register NewDef = MergeI->getOperand(Idx + 1).getReg();
-        MRI.replaceRegWith(MI.getOperand(Idx).getReg(), NewDef);
+        Register OldReg = MI.getOperand(Idx).getReg();
+        auto *OldRC = MRI.getRegClassOrNull(OldReg);
+        auto *NewRC = MRI.getRegClassOrNull(NewDef);
+        if ((!OldRC && !NewRC) || (OldRC && NewRC && OldRC == NewRC))
+          MRI.replaceRegWith(OldReg, NewDef);
+        else {
+          Builder.setInstr(MI);
+          Builder.buildInstr(TargetOpcode::COPY, {OldReg}, {NewDef});
+        }
         UpdatedDefs.push_back(NewDef);
       }
     }