HexagonOptAddrMode::changeStore - fix null dereference warning (PR43463)

[RKSimon]

Summary

As detailed on PR43463, this fixes a static analyzer null dereference warning by sinking Changed = true into the if() blocks where the MIB is actually created.

I did a quick check that suggested that one of those if() blocks is always guaranteed to be hit (so we could change it to if-else), but this seems like a safer approach.

llvm/lib/Target/Hexagon/HexagonOptAddrMode.cpp

if (HII->getAddrMode(*OldMI) == HexagonII::BaseRegOffset) {
       short NewOpCode = HII->changeAddrMode_rr_ur(*OldMI);
       assert(NewOpCode >= 0 && "Invalid New opcode\n");
       MIB = BuildMI(*BB, InsertPt, OldMI->getDebugLoc(), HII->get(NewOpCode));
       MIB.add(OldMI->getOperand(1));
       MIB.add(OldMI->getOperand(2));
       MIB.add(ImmOp);
       MIB.add(OldMI->getOperand(3));
       OpStart = 4;
+      Changed = true;
     } else if (HII->getAddrMode(*OldMI) == HexagonII::BaseImmOffset) {
       short NewOpCode = HII->changeAddrMode_io_abs(*OldMI);
       assert(NewOpCode >= 0 && "Invalid New opcode\n");
       MIB = BuildMI(*BB, InsertPt, OldMI->getDebugLoc(), HII->get(NewOpCode));
       const GlobalValue *GV = ImmOp.getGlobal();
       int64_t Offset = ImmOp.getOffset() + OldMI->getOperand(1).getImm();
       MIB.addGlobalAddress(GV, Offset, ImmOp.getTargetFlags());
       MIB.add(OldMI->getOperand(2));
       OpStart = 3;
-    }
       Changed = true;
-    LLVM_DEBUG(dbgs() << "[Changing]: " << *OldMI << "\n");
-    LLVM_DEBUG(dbgs() << "[TO]: " << *MIB << "\n");
+    }
   } else if (ImmOpNum == 1 && OldMI->getOperand(2).getImm() == 0) {
     short NewOpCode = HII->changeAddrMode_rr_io(*OldMI);
     assert(NewOpCode >= 0 && "Invalid New opcode\n");
     MIB = BuildMI(*BB, InsertPt, OldMI->getDebugLoc(), HII->get(NewOpCode));
     MIB.add(OldMI->getOperand(0));
     MIB.add(ImmOp);
     OpStart = 3;
     Changed = true;
+  }
+  if (Changed) {
     LLVM_DEBUG(dbgs() << "[Changing]: " << *OldMI << "\n");
     LLVM_DEBUG(dbgs() << "[TO]: " << *MIB << "\n");
-  }
-  if (Changed)
+
     for (unsigned i = OpStart; i < OpEnd; ++i)
       MIB.add(OldMI->getOperand(i));
+  }
 
   return Changed;
 }
 
 short HexagonOptAddrMode::getBaseWithLongOffset(const MachineInstr &MI) const {
   if (HII->getAddrMode(MI) == HexagonII::BaseImmOffset) {
     short TempOpCode = HII->changeAddrMode_io_rr(MI);
     return HII->changeAddrMode_rr_ur(TempOpCode);