[RISCV] Prevent using dummy_reg_pair_with_x0 in more places.

llvm/lib/Target/RISCV/RISCVExpandPseudoInsts.cpp

@@ -323,6 +323,8 @@ bool RISCVExpandPseudo::expandRV32ZdinxStore(MachineBasicBlock &MBB,
       TRI->getSubReg(MBBI->getOperand(0).getReg(), RISCV::sub_gpr_even);
   Register Hi =
       TRI->getSubReg(MBBI->getOperand(0).getReg(), RISCV::sub_gpr_odd);
+  if (Hi == RISCV::DUMMY_REG_PAIR_WITH_X0)
+    Hi = RISCV::X0;
 
   auto MIBLo = BuildMI(MBB, MBBI, DL, TII->get(RISCV::SW))
                    .addReg(Lo, getKillRegState(MBBI->getOperand(0).isKill()))
@@ -370,6 +372,7 @@ bool RISCVExpandPseudo::expandRV32ZdinxLoad(MachineBasicBlock &MBB,
       TRI->getSubReg(MBBI->getOperand(0).getReg(), RISCV::sub_gpr_even);
   Register Hi =
       TRI->getSubReg(MBBI->getOperand(0).getReg(), RISCV::sub_gpr_odd);
+  assert(Hi != RISCV::DUMMY_REG_PAIR_WITH_X0 && "Cannot write to X0_Pair");
 
   MachineInstrBuilder MIBLo, MIBHi;
 

llvm/lib/Target/RISCV/RISCVInstrInfo.cpp

@@ -543,16 +543,21 @@ void RISCVInstrInfo::copyPhysReg(MachineBasicBlock &MBB,
   }
 
   if (RISCV::GPRPairRegClass.contains(DstReg, SrcReg)) {
+    MCRegister EvenReg = TRI->getSubReg(SrcReg, RISCV::sub_gpr_even);
+    MCRegister OddReg = TRI->getSubReg(SrcReg, RISCV::sub_gpr_odd);
+    // We need to correct the odd register of X0_Pair.
+    if (OddReg == RISCV::DUMMY_REG_PAIR_WITH_X0)
+      OddReg == RISCV::X0;
+    assert(DstReg != RISCV::X0_Pair && "Cannot write to X0_Pair");
+
     // Emit an ADDI for both parts of GPRPair.
     BuildMI(MBB, MBBI, DL, get(RISCV::ADDI),
             TRI->getSubReg(DstReg, RISCV::sub_gpr_even))
-        .addReg(TRI->getSubReg(SrcReg, RISCV::sub_gpr_even),
-                getKillRegState(KillSrc))
+        .addReg(EvenReg, getKillRegState(KillSrc))
         .addImm(0);
     BuildMI(MBB, MBBI, DL, get(RISCV::ADDI),
             TRI->getSubReg(DstReg, RISCV::sub_gpr_odd))
-        .addReg(TRI->getSubReg(SrcReg, RISCV::sub_gpr_odd),
-                getKillRegState(KillSrc))
+        .addReg(OddReg, getKillRegState(KillSrc))
         .addImm(0);
     return;
   }