diff --git a/llvm/lib/Target/RISCV/RISCVMergeBaseOffset.cpp b/llvm/lib/Target/RISCV/RISCVMergeBaseOffset.cpp
--- a/llvm/lib/Target/RISCV/RISCVMergeBaseOffset.cpp
+++ b/llvm/lib/Target/RISCV/RISCVMergeBaseOffset.cpp
@@ -140,6 +140,8 @@
   if (Hi.getOpcode() != RISCV::AUIPC)
     Lo.getOperand(2).setOffset(Offset);
   // Delete the tail instruction.
+  MRI->constrainRegClass(Lo.getOperand(0).getReg(),
+                         MRI->getRegClass(Tail.getOperand(0).getReg()));
   MRI->replaceRegWith(Tail.getOperand(0).getReg(), Lo.getOperand(0).getReg());
   Tail.eraseFromParent();
   LLVM_DEBUG(dbgs() << "  Merged offset " << Offset << " into base.\n"