[RegisterCoalescer] fix subregister index in remat call

[ivafanas]

Summary

TII->reMaterialize accepts sub register index which denotes dst reg substituion. DstIdx should be passed instead of SrcIdx, because SrcIdx relates to another register.

llvm/lib/CodeGen/RegisterCoalescer.cpp

bool RegisterCoalescer::reMaterializeTrivialDef(const CoalescerPair &CP,
 
   if (!allUsesAvailableAt(DefMI, ValNo->def, CopyIdx))
     return false;
 
   DebugLoc DL = CopyMI->getDebugLoc();
   MachineBasicBlock *MBB = CopyMI->getParent();
   MachineBasicBlock::iterator MII =
     std::next(MachineBasicBlock::iterator(CopyMI));
-  TII->reMaterialize(*MBB, MII, DstReg, SrcIdx, *DefMI, *TRI);
+  TII->reMaterialize(*MBB, MII, DstReg, DstIdx, *DefMI, *TRI);
   MachineInstr &NewMI = *std::prev(MII);
   NewMI.setDebugLoc(DL);
 
   // In a situation like the following:
   //     %0:subreg = instr              ; DefMI, subreg = DstIdx
   //     %1        = copy %0:subreg ; CopyMI, SrcIdx = 0
   // instead of widening %1 to the register class of %0 simply do:
   //     %1 = instr