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;
}
/// 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;
}