/// TODO: Refactor this code so the decision on whether or not to accept an
/// instruction.
bool swift::getFinalReleasesForValue(SILValue V, ReleaseTracker &Tracker) {
llvm::SmallPtrSet<SILBasicBlock *, 16> LiveIn;
llvm::SmallPtrSet<SILBasicBlock *, 16> UseBlocks;
// First attempt to get the BB where this value resides.
auto *DefBB = V->getParentBB();
if (!DefBB)
return false;
bool seenRelease = false;
SILInstruction *OneRelease = nullptr;
// We'll treat this like a liveness problem where the value is the def. Each
// block that has a use of the value has the value live-in unless it is the
// block with the value.
for (auto *UI : V->getUses()) {
auto *User = UI->getUser();
auto *BB = User->getParent();
if (!Tracker.isUserAcceptable(User))
return false;
Tracker.trackUser(User);
if (BB != DefBB)
LiveIn.insert(BB);
// Also keep track of the blocks with uses.
UseBlocks.insert(BB);
// Try to speed up the trivial case of single release/dealloc.
if (isa<StrongReleaseInst>(User) || isa<DeallocBoxInst>(User)) {
if (!seenRelease)
OneRelease = User;
else
OneRelease = nullptr;
seenRelease = true;
}
}
// Only a single release/dealloc? We're done!
if (OneRelease) {
Tracker.trackLastRelease(OneRelease);
return true;
}
propagateLiveness(LiveIn, DefBB);
// Now examine each block we saw a use in. If it has no successors
// that are in LiveIn, then the last use in the block is the final
// release/dealloc.
for (auto *BB : UseBlocks)
if (!successorHasLiveIn(BB, LiveIn))
if (!addLastUse(V, BB, Tracker))
return false;
return true;
}
// Walk backwards in BB looking for the last use of a given
// value, and add it to the set of release points.
static bool addLastUse(SILValue V, SILBasicBlock *BB,
ReleaseTracker &Tracker) {
for (auto I = BB->rbegin(); I != BB->rend(); ++I) {
if (Tracker.isUser(&*I)) {
Tracker.trackLastRelease(&*I);
return true;
}
}
llvm_unreachable("BB is expected to have a use of a closure");
return false;
}
// Walk backwards in BB looking for the last use of a given
// value, and add it to the set of release points.
static bool addLastUse(SILValue V, SILBasicBlock *BB,
ReleaseTracker &Tracker) {
for (auto I = BB->rbegin(); I != BB->rend(); ++I) {
for (auto &Op : I->getAllOperands())
if (Op.get() == V) {
Tracker.trackLastRelease(&*I);
return true;
}
}
llvm_unreachable("BB is expected to have a use of a closure");
return false;
}
