[AMDGPU][Scheduler] Fix usage of TII.reMaterialize (NFC) (llvm#150259)

Any non-zero `SubIdx` passed to the method is composed with the
rematerialized instruction's first operand's subregister to determine
the new register's subregister. In our case we want the new register to
have the same subregister as the old one, so we should pass 0.

Author: lucas-rami

llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp

@@ -1911,14 +1911,12 @@ void PreRARematStage::rematerialize() {
   for (auto &[DefMI, Remat] : Rematerializations) {
     MachineBasicBlock::iterator InsertPos(Remat.UseMI);
     Register Reg = DefMI->getOperand(0).getReg();
-    unsigned SubReg = DefMI->getOperand(0).getSubReg();
     unsigned DefRegion = MIRegion.at(DefMI);
 
     // Rematerialize DefMI to its use block.
-    TII->reMaterialize(*InsertPos->getParent(), InsertPos, Reg, SubReg, *DefMI,
+    TII->reMaterialize(*InsertPos->getParent(), InsertPos, Reg, 0, *DefMI,
                        *DAG.TRI);
     Remat.RematMI = &*std::prev(InsertPos);
-    Remat.RematMI->getOperand(0).setSubReg(SubReg);
     DAG.LIS->InsertMachineInstrInMaps(*Remat.RematMI);
 
     // Update region boundaries in regions we sinked from (remove defining MI)
@@ -2064,14 +2062,12 @@ void PreRARematStage::finalizeGCNSchedStage() {
     MachineBasicBlock::iterator InsertPos(DAG.Regions[DefRegion].second);
     MachineBasicBlock *MBB = RegionBB[DefRegion];
     Register Reg = RematMI.getOperand(0).getReg();
-    unsigned SubReg = RematMI.getOperand(0).getSubReg();
 
     // Re-rematerialize MI at the end of its original region. Note that it may
     // not be rematerialized exactly in the same position as originally within
     // the region, but it should not matter much.
-    TII->reMaterialize(*MBB, InsertPos, Reg, SubReg, RematMI, *DAG.TRI);
+    TII->reMaterialize(*MBB, InsertPos, Reg, 0, RematMI, *DAG.TRI);
     MachineInstr *NewMI = &*std::prev(InsertPos);
-    NewMI->getOperand(0).setSubReg(SubReg);
     DAG.LIS->InsertMachineInstrInMaps(*NewMI);
 
     auto UseRegion = MIRegion.find(Remat.UseMI);