[AVR][NFC] Eliminate warning 'unused variable'

[benshi001]

The variable STI is only used in assert, so there will be 'used variable' warnings when doing release build.

[Patryk27]

llvm/lib/Target/AVR/AVRExpandPseudoInsts.cpp

1221–1222

I kinda like assert(expression && ....);, since it prints the asserted expression - maybe we can use the void-casting trick we already have for "pseudo expand limit reached"?

Say:

assert(STI. && ...);
(void)STI;

llvm/lib/Target/AVR/AVRExpandPseudoInsts.cpp

bool AVRExpandPseudo::expand<AVR::STDSPQRr>(Block &MBB, BlockIt MBBI) {
   MachineInstr &MI = *MBBI;
   const MachineFunction &MF = *MBB.getParent();
   const AVRSubtarget &STI = MF.getSubtarget<AVRSubtarget>();
 
   assert(MI.getOperand(0).getReg() == AVR::SP &&
          "SP is expected as base pointer");
 
   assert(STI.getFrameLowering()->hasReservedCallFrame(MF) &&
          "unexpected STDSPQRr pseudo instruction");
+  (void)STI;
 
   MI.setDesc(TII->get(AVR::STDPtrQRr));
   MI.getOperand(0).setReg(AVR::R29R28);
 
   return true;
 }
 
 template <>
 bool AVRExpandPseudo::expand<AVR::STDWSPQRr>(Block &MBB, BlockIt MBBI) {
   MachineInstr &MI = *MBBI;
   const MachineFunction &MF = *MBB.getParent();
   const AVRSubtarget &STI = MF.getSubtarget<AVRSubtarget>();
 
   assert(MI.getOperand(0).getReg() == AVR::SP &&
          "SP is expected as base pointer");
 
   assert(STI.getFrameLowering()->hasReservedCallFrame(MF) &&
          "unexpected STDWSPQRr pseudo instruction");
+  (void)STI;
 
   MI.setDesc(TII->get(AVR::STDWPtrQRr));
   MI.getOperand(0).setReg(AVR::R29R28);
 
   return true;
 }
 
 template <>