ARCAnalysis: fix canNeverUseObject to correctly handle builtins.

include/swift/SILOptimizer/Analysis/ARCAnalysis.h

@@ -72,12 +72,13 @@ bool mustGuaranteedUseValue(SILInstruction *User, SILValue Ptr,
 /// Returns true if \p Inst can never conservatively decrement reference counts.
 bool canNeverDecrementRefCounts(SILInstruction *Inst);
 
-/// \returns True if \p User can never use a value in a way that requires the
-/// value to be alive.
+/// Returns true if \p Inst may access any indirect object either via an address
+/// or reference.
 ///
-/// This is purposefully a negative query to contrast with canUseValue which is
-/// about a specific value while this is about general values.
-bool canNeverUseValues(SILInstruction *User);
+/// If false is returned and \p Inst has an address or reference type operand,
+/// then \p Inst only operates on the value of the address itself, not the
+/// memory. i.e. it does not dereference the address.
+bool canUseObject(SILInstruction *Inst);
 
 /// \returns true if the user \p User may use \p Ptr in a manner that requires
 /// Ptr's life to be guaranteed to exist at this point.

lib/SILOptimizer/ARC/ARCRegionState.cpp

@@ -531,7 +531,9 @@ void ARCRegionState::summarizeBlock(SILBasicBlock *BB) {
   SummarizedInterestingInsts.clear();
 
   for (auto &I : *BB)
-    if (!canNeverUseValues(&I) || I.mayReleaseOrReadRefCount() ||
+    // FIXME: mayReleaseOrReadRefCount should be a strict subset of
+    // canUseObject. If not, there is a bug in canUseObject.
+    if (canUseObject(&I) || I.mayReleaseOrReadRefCount() ||
         isStrongEntranceInstruction(I))
       SummarizedInterestingInsts.push_back(&I);
 }

lib/SILOptimizer/Analysis/ARCAnalysis.cpp

@@ -91,7 +91,7 @@ bool swift::mayDecrementRefCount(SILInstruction *User,
 //                                Use Analysis
 //===----------------------------------------------------------------------===//
 
-/// Returns true if a builtin apply cannot use reference counted values.
+/// Returns true if a builtin apply can use reference counted values.
 ///
 /// The main case that this handles here are builtins that via read none imply
 /// that they cannot read globals and at the same time do not take any
@@ -106,28 +106,33 @@ static bool canApplyOfBuiltinUseNonTrivialValues(BuiltinInst *BInst) {
     if (II.hasAttribute(llvm::Attribute::ReadNone)) {
       for (auto &Op : BInst->getAllOperands()) {
         if (!Op.get()->getType().isTrivial(*F)) {
-          return false;
+          return true;
         }
       }
     }
 
-    return true;
+    return false;
   }
 
   auto &BI = BInst->getBuiltinInfo();
-  if (BI.isReadNone()) {
-    for (auto &Op : BInst->getAllOperands()) {
-      if (!Op.get()->getType().isTrivial(*F)) {
-        return false;
-      }
+  if (!BI.isReadNone())
+    return true;
+
+  for (auto &Op : BInst->getAllOperands()) {
+    if (!Op.get()->getType().isTrivial(*F)) {
+      return true;
     }
   }
-
-  return true;
+  return false;
 }
 
-/// Returns true if Inst is a function that we know never uses ref count values.
-bool swift::canNeverUseValues(SILInstruction *Inst) {
+/// Returns true if \p Inst may access any indirect object either via an address
+/// or reference.
+///
+/// If these instructions do have an address or reference type operand, then
+/// they only operate on the value of the address itself, not the
+/// memory. i.e. they don't dereference the address.
+bool swift::canUseObject(SILInstruction *Inst) {
   switch (Inst->getKind()) {
   // These instructions do not use other values.
   case SILInstructionKind::FunctionRefInst:
@@ -142,33 +147,36 @@ bool swift::canNeverUseValues(SILInstruction *Inst) {
   case SILInstructionKind::AllocBoxInst:
   case SILInstructionKind::MetatypeInst:
   case SILInstructionKind::WitnessMethodInst:
-    return true;
+    return false;
 
   // DeallocStackInst do not use reference counted values.
   case SILInstructionKind::DeallocStackInst:
-    return true;
+    return false;
 
   // Debug values do not use referenced counted values in a manner we care
   // about.
   case SILInstructionKind::DebugValueInst:
   case SILInstructionKind::DebugValueAddrInst:
-    return true;
+    return false;
 
   // Casts do not use pointers in a manner that we care about since we strip
   // them during our analysis. The reason for this is if the cast is not dead
   // then there must be some other use after the cast that we will protect if a
   // release is not in between the cast and the use.
+  //
+  // Note: UncheckedRefCastAddrInst moves a reference into a new object. While
+  // the net reference count should be zero, there's no guarantee it won't
+  // access the object.
   case SILInstructionKind::UpcastInst:
   case SILInstructionKind::AddressToPointerInst:
   case SILInstructionKind::PointerToAddressInst:
   case SILInstructionKind::UncheckedRefCastInst:
-  case SILInstructionKind::UncheckedRefCastAddrInst:
   case SILInstructionKind::UncheckedAddrCastInst:
   case SILInstructionKind::RefToRawPointerInst:
   case SILInstructionKind::RawPointerToRefInst:
   case SILInstructionKind::UnconditionalCheckedCastInst:
   case SILInstructionKind::UncheckedBitwiseCastInst:
-    return true;
+    return false;
 
   // If we have a trivial bit cast between trivial types, it is not something
   // that can use ref count ops in a way we care about. We do need to be careful
@@ -183,7 +191,7 @@ bool swift::canNeverUseValues(SILInstruction *Inst) {
   // safe.
   case SILInstructionKind::UncheckedTrivialBitCastInst: {
     SILValue Op = cast<UncheckedTrivialBitCastInst>(Inst)->getOperand();
-    return Op->getType().isTrivial(*Inst->getFunction());
+    return !Op->getType().isTrivial(*Inst->getFunction());
   }
 
   // Typed GEPs do not use pointers. The user of the typed GEP may but we will
@@ -198,18 +206,18 @@ bool swift::canNeverUseValues(SILInstruction *Inst) {
   case SILInstructionKind::UncheckedEnumDataInst:
   case SILInstructionKind::IndexAddrInst:
   case SILInstructionKind::IndexRawPointerInst:
-      return true;
+    return false;
 
   // Aggregate formation by themselves do not create new uses since it is their
   // users that would create the appropriate uses.
   case SILInstructionKind::EnumInst:
   case SILInstructionKind::StructInst:
   case SILInstructionKind::TupleInst:
-    return true;
+    return false;
 
   // Only uses non reference counted values.
   case SILInstructionKind::CondFailInst:
-    return true;
+    return false;
 
   case SILInstructionKind::BuiltinInst: {
     auto *BI = cast<BuiltinInst>(Inst);
@@ -221,9 +229,9 @@ bool swift::canNeverUseValues(SILInstruction *Inst) {
   // dead, LLVM will clean it up.
   case SILInstructionKind::BranchInst:
   case SILInstructionKind::CondBranchInst:
-    return true;
-  default:
     return false;
+  default:
+    return true;
   }
 }
 
@@ -268,14 +276,15 @@ static bool canTerminatorUseValue(TermInst *TI, SILValue Ptr,
 
 
 bool swift::mayHaveSymmetricInterference(SILInstruction *User, SILValue Ptr, AliasAnalysis *AA) {
+  // If Inst is an instruction that we know can never use values with reference
+  // semantics, return true. Check this before AliasAnalysis because some memory
+  // operations, like dealloc_stack, don't use ref counted values.
+  if (!canUseObject(User))
+    return false;
+
   // Check whether releasing this value can call deinit and interfere with User.
   if (AA->mayValueReleaseInterfereWithInstruction(User, Ptr))
     return true;
-
-  // If Inst is an instruction that we know can never use values with reference
-  // semantics, return true.
-  if (canNeverUseValues(User))
-    return false;
 
   // If the user is a load or a store and we can prove that it does not access
   // the object then return true.

test/SILOptimizer/existential_transform.swift

@@ -301,8 +301,8 @@ func wrap_gcp<T:GP>(_ a:T,_ b:GP) -> Int {
 // CHECK: strong_retain 
 // CHECK: apply
 // CHECK: destroy_addr 
-// CHECK: dealloc_stack
 // CHECK: strong_release 
+// CHECK: dealloc_stack
 // CHECK: return 
 // CHECK: } // end sil function '$s21existential_transform3gcpySixAA2GPRzlF'
 @inline(never) func gcp<T:GP>(_ a:T) -> Int {
@@ -328,8 +328,8 @@ func wrap_gcp_arch<T:GP>(_ a:T,_ b:GP, _ c:inout Array<T>) -> Int {
 // CHECK: strong_retain
 // CHECK: apply
 // CHECK: destroy_addr
-// CHECK: dealloc_stack
 // CHECK: strong_release
+// CHECK: dealloc_stack
 // CHECK: return
 // CHECK-LABEL: } // end sil function '$s21existential_transform8gcp_archySix_SayxGztAA2GPRzlF'
 @inline(never) func gcp_arch<T:GP>(_ a:T, _ b:inout Array<T>) -> Int {

test/SILOptimizer/retain_release_code_motion.sil

@@ -718,3 +718,43 @@ bb2:
   return %9999 : $()
 }
 
+// Hoist releases above dealloc_stack
+// CHECK-LABEL: sil @testReleaseHoistDeallocStack : $@convention(thin) (AnyObject) -> () {
+// CHECK: bb0(%0 : $AnyObject):
+// CHECK-NOT:  retain
+// CHECK:      [[A:%.*]] = alloc_stack $Int64
+// CHECK-NEXT  dealloc_stack [[A]] : $*Int64
+// CHECK-NOT:  release
+// CHECK-LABEL: } // end sil function 'testReleaseHoistDeallocStack'
+sil @testReleaseHoistDeallocStack : $@convention(thin) (AnyObject)->() {
+bb0(%0 : $AnyObject):
+  strong_retain %0 : $AnyObject
+  %alloc = alloc_stack $Int64
+  dealloc_stack %alloc : $*Int64
+  strong_release %0 : $AnyObject
+  %34 = tuple ()
+  return %34 : $()
+}
+
+// Do not hoist releases above builtins that operate on object references.
+//
+// CHECK-RELEASE-HOISTING-LABEL: sil @testCopyArray : $@convention(thin) (_ContiguousArrayBuffer<AnyObject>, Builtin.Word, Builtin.Word) -> Builtin.RawPointer {
+// CHECK-RELEASE-HOISTING: bb0(%0 : $_ContiguousArrayBuffer<AnyObject>, %1 : $Builtin.Word, %2 : $Builtin.Word):
+// CHECK-RELEASE-HOISTING:   builtin "copyArray"<AnyObject>
+// CHECK-RELEASE-HOISTING:   release_value %0 : $_ContiguousArrayBuffer<AnyObject>
+// CHECK-RELEASE-HOISTING-LABEL: } // end sil function 'testCopyArray'
+sil @testCopyArray : $@convention(thin) (_ContiguousArrayBuffer<AnyObject>, Builtin.Word, Builtin.Word) -> Builtin.RawPointer {
+bb0(%0 : $_ContiguousArrayBuffer<AnyObject>, %1 : $Builtin.Word, %2 : $Builtin.Word):
+  %eltty = metatype $@thick AnyObject.Protocol
+  %newptr = builtin "allocRaw"(%1 : $Builtin.Word, %1 : $Builtin.Word) : $Builtin.RawPointer
+  bind_memory %newptr : $Builtin.RawPointer, %1 : $Builtin.Word to $*AnyObject
+  %storage = struct_extract %0 : $_ContiguousArrayBuffer<AnyObject>, #_ContiguousArrayBuffer._storage
+  %elements = ref_tail_addr %storage : $__ContiguousArrayStorageBase, $AnyObject
+  %eltptr = address_to_pointer %elements : $*AnyObject to $Builtin.RawPointer
+  %objptr = struct $UnsafePointer<AnyObject> (%eltptr : $Builtin.RawPointer)
+  %ptrdep = mark_dependence %objptr : $UnsafePointer<AnyObject> on %storage : $__ContiguousArrayStorageBase
+  %rawptr = struct_extract %ptrdep : $UnsafePointer<AnyObject>, #UnsafePointer._rawValue
+  %copy = builtin "copyArray"<AnyObject>(%eltty : $@thick AnyObject.Protocol, %newptr : $Builtin.RawPointer, %rawptr : $Builtin.RawPointer, %1 : $Builtin.Word) : $()
+  release_value %0 : $_ContiguousArrayBuffer<AnyObject>
+  return %newptr : $Builtin.RawPointer
+}