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DeadObjectElimination: Handle alloc_ref in ossa

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This commit is contained in:
Meghana Gupta
2023-07-23 23:37:10 -07:00
parent f5c5c9e36b
commit c3c78fa8f8
1 changed files with 66 additions and 35 deletions
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101
lib/SILOptimizer/Transforms/DeadObjectElimination.cpp
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@@ -177,13 +177,22 @@ static DestructorEffects doesDestructorHaveSideEffects(AllocRefInstBase *ARI) {
assert(RefInst->getNumOperands() == 1 &&
"Make sure RefInst only has one argument.");
LLVM_DEBUG(llvm::dbgs() << " SAFE! Ref count operation on "
"Self.\n");
"Self.\n");
continue;
} else {
LLVM_DEBUG(llvm::dbgs() << " UNSAFE! Ref count operation "
"not on self.\n");
return DestructorEffects::Unknown;
}
LLVM_DEBUG(llvm::dbgs() << " UNSAFE! Ref count operation "
"not on self.\n");
return DestructorEffects::Unknown;
}
if (auto *destroy = dyn_cast<DestroyValueInst>(&I)) {
if (stripCasts(destroy->getOperand()) == Self) {
LLVM_DEBUG(llvm::dbgs() << " SAFE! Ref count operation on "
"Self.\n");
continue;
}
LLVM_DEBUG(llvm::dbgs() << " UNSAFE! Ref count operation "
"not on self.\n");
return DestructorEffects::Unknown;
}
// dealloc_stack can be ignored.
@@ -246,7 +255,15 @@ static DestructorEffects doesDestructorHaveSideEffects(AllocRefInstBase *ARI) {
/// alloc_ref alive.
static bool canZapInstruction(SILInstruction *Inst, bool acceptRefCountInsts,
bool onlyAcceptTrivialStores) {
if (isa<SetDeallocatingInst>(Inst) || isa<FixLifetimeInst>(Inst))
if (isa<DestroyValueInst>(Inst)) {
return acceptRefCountInsts;
}
if (isa<CopyValueInst>(Inst) || isa<BeginBorrowInst>(Inst) ||
isa<MoveValueInst>(Inst)) {
return true;
}
if (isa<SetDeallocatingInst>(Inst) || isa<FixLifetimeInst>(Inst) ||
isa<EndBorrowInst>(Inst))
return true;
// It is ok to eliminate various retains/releases. We are either removing
@@ -384,6 +401,7 @@ hasUnremovableUsers(SILInstruction *allocation, UserList *Users,
LLVM_DEBUG(llvm::dbgs() << " Analyzing Use Graph.");
SmallVector<RefElementAddrInst *, 8> refElementAddrs;
BuiltinInst *destroyArray = nullptr;
auto *allocRef = dyn_cast<AllocRefInstBase>(allocation);
@@ -397,11 +415,10 @@ hasUnremovableUsers(SILInstruction *allocation, UserList *Users,
if (Users && !Users->insert(I)) {
LLVM_DEBUG(llvm::dbgs() << " Already seen skipping...\n");
continue;
}
if (auto *rea = dyn_cast<RefElementAddrInst>(I)) {
} else if (auto *rea = dyn_cast<RefElementAddrInst>(I)) {
if (rea != allocation && !rea->getType().isTrivial(*rea->getFunction()))
refElementAddrs.push_back(rea);
} else if (allocRef && Users && isDestroyArray(I)) {
} else if (allocRef && isDestroyArray(I)) {
if (destroyArray)
return true;
destroyArray = cast<BuiltinInst>(I);
@@ -434,20 +451,20 @@ hasUnremovableUsers(SILInstruction *allocation, UserList *Users,
}
}
// In OSSA, we don't have to do this check. We can always accept a
// destroyArray and insert the compensating destroys right at the store
// instructions.
if (destroyArray)
return !onlyStoresToTailObjects(destroyArray, *Users, allocRef);
// In non-OSSA we cannot reliably track the lifetime of non-trivial stored
// properties. Removing the dead alloc_ref might leak a property value.
// TODO: in OSSA we can replace stores to properties with a destroy_value.
for (RefElementAddrInst *rea : refElementAddrs) {
// Re-run the check with not accepting non-trivial stores.
if (hasUnremovableUsers(rea, nullptr, acceptRefCountInsts,
/*onlyAcceptTrivialStores*/ true))
return true;
if (!allocation->getFunction()->hasOwnership()) {
// In non-ossa, if we found a destroy array builtin that destroys the tail
// elements, ensure all stores are to the taile elems.
if (destroyArray) {
return !onlyStoresToTailObjects(destroyArray, *Users, allocRef);
}
// In non-OSSA we cannot reliably track the lifetime of non-trivial stored
// properties. Removing the dead alloc_ref might leak a property value.
for (RefElementAddrInst *rea : refElementAddrs) {
// Re-run the check with not accepting non-trivial stores.
if (hasUnremovableUsers(rea, nullptr, acceptRefCountInsts,
/*onlyAcceptTrivialStores*/ true))
return true;
}
}
return false;
@@ -820,21 +837,35 @@ bool DeadObjectElimination::processAllocRef(AllocRefInstBase *ARI) {
return false;
}
// Find the instruction which releases the object's tail elements.
SILInstruction *releaseOfTailElems = nullptr;
for (SILInstruction *user : UsersToRemove) {
if (isDestroyArray(user) ||
(destructorEffects == DestructorEffects::DestroysTailElems &&
isa<RefCountingInst>(user) && user->mayRelease())) {
// Bail if we find multiple such instructions.
if (releaseOfTailElems)
if (!ARI->getFunction()->hasOwnership()) {
// Find the instruction which releases the object's tail elements.
SILInstruction *releaseOfTailElems = nullptr;
for (SILInstruction *user : UsersToRemove) {
if (isDestroyArray(user) ||
(destructorEffects == DestructorEffects::DestroysTailElems &&
isa<RefCountingInst>(user) && user->mayRelease())) {
// Bail if we find multiple such instructions.
if (releaseOfTailElems)
return false;
releaseOfTailElems = user;
}
}
if (releaseOfTailElems) {
if (!insertCompensatingReleases(releaseOfTailElems, UsersToRemove)) {
return false;
releaseOfTailElems = user;
}
}
}
if (releaseOfTailElems) {
if (!insertCompensatingReleases(releaseOfTailElems, UsersToRemove)) {
return false;
if (ARI->getFunction()->hasOwnership()) {
for (auto *user : UsersToRemove) {
auto *store = dyn_cast<StoreInst>(user);
if (!store ||
store->getOwnershipQualifier() == StoreOwnershipQualifier::Trivial) {
continue;
}
SILBuilderWithScope(store).createDestroyValue(store->getLoc(),
store->getSrc());
}
}