void accessesGlobal(StoreInst* SI) {
  Value *V = SI->getPointerOperand();
  if (isa<GlobalValue>(V))
    return true;
  if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
    if (CE->getOpcode() == Instruction::GetElementPtr)
      if (isa<GlobalValue>(CE->getOperand(0)))
        return true;
  return false;
}