Пример #1
0
bool AliasAnalysis::canApplyDecrementRefCount(FullApplySite FAS, SILValue Ptr) {
  // Treat applications of @noreturn functions as decrementing ref counts. This
  // causes the apply to become a sink barrier for ref count increments.
  if (FAS.getCallee().getType().getAs<SILFunctionType>()->isNoReturn())
    return true;

  /// If the pointer cannot escape to the function we are done.
  if (!EA->canEscapeTo(Ptr, FAS))
    return false;

  SideEffectAnalysis::FunctionEffects ApplyEffects;
  SEA->getEffects(ApplyEffects, FAS);

  auto &GlobalEffects = ApplyEffects.getGlobalEffects();
  if (ApplyEffects.mayReadRC() || GlobalEffects.mayRelease())
    return true;

  /// The function has no unidentified releases, so let's look at the arguments
  // in detail.
  for (unsigned Idx = 0, End = FAS.getNumArguments(); Idx < End; ++Idx) {
    auto &ArgEffect = ApplyEffects.getParameterEffects()[Idx];
    if (ArgEffect.mayRelease()) {
      // The function may release this argument, so check if the pointer can
      // escape to it.
      if (EA->canEscapeToValue(Ptr, FAS.getArgument(Idx)))
        return true;
    }
  }
  return false;
}
Пример #2
0
/// Returns true if the \p MayWrites set contains any memory writes which may
/// alias with any memory which is read by \p AI.
static bool mayWriteTo(AliasAnalysis *AA, SideEffectAnalysis *SEA,
                       WriteSet &MayWrites, ApplyInst *AI) {
  SideEffectAnalysis::FunctionEffects E;
  SEA->getEffects(E, AI);
  assert(E.getMemBehavior(RetainObserveKind::IgnoreRetains) <=
         SILInstruction::MemoryBehavior::MayRead &&
         "apply should only read from memory");
  if (E.getGlobalEffects().mayRead() && !MayWrites.empty()) {
    // We don't know which memory is read in the callee. Therefore we bail if
    // there are any writes in the loop.
    return true;
  }

  for (unsigned Idx = 0, End = AI->getNumArguments(); Idx < End; ++Idx) {
    auto &ArgEffect = E.getParameterEffects()[Idx];
    if (!ArgEffect.mayRead())
      continue;

    SILValue Arg = AI->getArgument(Idx);

    // Check if the memory addressed by the argument may alias any writes.
    for (auto *W : MayWrites) {
      if (AA->mayWriteToMemory(W, Arg)) {
        DEBUG(llvm::dbgs() << "  mayWriteTo\n" << *W << " to " << *AI << "\n");
        return true;
      }
    }
  }
  return false;
}