Merge pull request #42378 from atrick/5.7-fix-cast-ownership

5.7 fix cast ownership

Author: atrick

include/swift/AST/Types.h

@@ -1248,6 +1248,10 @@ class alignas(1 << TypeAlignInBits) TypeBase
   /// Whether this is the AnyObject type.
   bool isAnyObject();
 
+  /// Return true if this type is potentially an AnyObject existential after
+  /// substitution.
+  bool isPotentiallyAnyObject();
+
   /// Whether this is an existential composition containing
   /// Error.
   bool isExistentialWithError();

include/swift/SIL/DynamicCasts.h

@@ -35,6 +35,11 @@ class SILType;
 enum class CastConsumptionKind : uint8_t;
 struct SILDynamicCastInst;
 
+/// Returns true if the ownership of all references in this type are preserved
+/// (without unbalanced retains or releases) during dynamic casting.
+bool doesCastPreserveOwnershipForTypes(SILModule &module, CanType sourceType,
+                                       CanType targetType);
+
 enum class DynamicCastFeasibility {
   /// The cast will always succeed.
   WillSucceed,
@@ -82,10 +87,17 @@ bool emitSuccessfulIndirectUnconditionalCast(
 bool emitSuccessfulIndirectUnconditionalCast(SILBuilder &B, SILLocation loc,
                                              SILDynamicCastInst dynamicCast);
 
+/// Can the given cast be performed by the scalar checked-cast instructions in
+/// the current SIL stage, or do we need to use the indirect instructions?
+bool canSILUseScalarCheckedCastInstructions(SILModule &M,
+                                            CanType sourceType,
+                                            CanType targetType);
+
 /// Can the given cast be performed by the scalar checked-cast
-/// instructions, or does we need to use the indirect instructions?
-bool canUseScalarCheckedCastInstructions(SILModule &M,
-                                         CanType sourceType,CanType targetType);
+/// instructions at IRGen, or do we need to use the indirect instructions?
+bool canIRGenUseScalarCheckedCastInstructions(SILModule &M,
+                                              CanType sourceType,
+                                              CanType targetType);
 
 /// Carry out the operations required for an indirect conditional cast
 /// using a scalar cast operation.
@@ -435,8 +447,8 @@ struct SILDynamicCastInst {
     llvm_unreachable("covered switch");
   }
 
-  bool canUseScalarCheckedCastInstructions() const {
-    return swift::canUseScalarCheckedCastInstructions(
+  bool canSILUseScalarCheckedCastInstructions() const {
+    return swift::canSILUseScalarCheckedCastInstructions(
         getModule(), getSourceFormalType(), getTargetFormalType());
   }
 };

include/swift/SIL/OwnershipUtils.h

@@ -189,9 +189,9 @@ class ForwardingOperand {
     return use->getOwnershipConstraint();
   }
 
-  bool isDirectlyForwarding() const {
+  bool preservesOwnership() const {
     auto &mixin = *OwnershipForwardingMixin::get(use->getUser());
-    return mixin.isDirectlyForwarding();
+    return mixin.preservesOwnership();
   }
 
   ValueOwnershipKind getForwardingOwnershipKind() const;

include/swift/SIL/SILInstruction.h

@@ -1112,39 +1112,31 @@ class CopyLikeInstruction {
 /// initializes the kind field on our object is run before our constructor runs.
 class OwnershipForwardingMixin {
   ValueOwnershipKind ownershipKind;
-  bool directlyForwards;
+  bool preservesOwnershipFlag;
 
 protected:
   OwnershipForwardingMixin(SILInstructionKind kind,
                            ValueOwnershipKind ownershipKind,
-                           bool isDirectlyForwarding = true)
-      : ownershipKind(ownershipKind), directlyForwards(isDirectlyForwarding) {
+                           bool preservesOwnership = true)
+      : ownershipKind(ownershipKind),
+        preservesOwnershipFlag(preservesOwnership) {
     assert(isa(kind) && "Invalid subclass?!");
     assert(ownershipKind && "invalid forwarding ownership");
-    assert((directlyForwards || ownershipKind != OwnershipKind::Guaranteed) &&
+    assert((preservesOwnershipFlag
+            || ownershipKind != OwnershipKind::Guaranteed) &&
            "Non directly forwarding instructions can not forward guaranteed "
            "ownership");
   }
 
 public:
-  /// If an instruction is directly forwarding, then any operand op whose
-  /// ownership it forwards into a result r must have the property that op and r
-  /// are "rc identical". This means that they are representing the same set of
-  /// underlying lifetimes (plural b/c of aggregates).
+  /// A forwarding instruction preserved ownership if it has a
+  /// dynamically non-trivial result in which all references are forwarded from
+  /// the operand.
   ///
-  /// An instruction that is not directly forwarding, can not have guaranteed
-  /// ownership since without direct forwarding, there isn't necessarily any
-  /// connection in between the operand's lifetime and the value's lifetime.
-  ///
-  /// An example of this is checked_cast_br where when performing the following:
-  ///
-  ///   __SwiftValue(AnyHashable(Klass())) to OtherKlass()
-  ///
-  /// we will look through the __SwiftValue(AnyHashable(X)) any just cast Klass
-  /// to OtherKlass. This means that the result argument would no longer be
-  /// rc-identical to the operand and default case and thus we can not propagate
-  /// forward any form of guaranteed ownership.
-  bool isDirectlyForwarding() const { return directlyForwards; }
+  /// A cast can only forward guaranteed values if it preserves ownership. Such
+  /// casts cannot release any references within their operand's value and
+  /// cannot retain any references owned by their result.
+  bool preservesOwnership() const { return preservesOwnershipFlag; }
 
   /// Forwarding ownership is determined by the forwarding instruction's
   /// constant ownership attribute. If forwarding ownership is owned, then the
@@ -1160,7 +1152,7 @@ class OwnershipForwardingMixin {
     return ownershipKind;
   }
   void setForwardingOwnershipKind(ValueOwnershipKind newKind) {
-    assert((isDirectlyForwarding() || newKind != OwnershipKind::Guaranteed) &&
+    assert((preservesOwnership() || newKind != OwnershipKind::Guaranteed) &&
            "Non directly forwarding instructions can not forward guaranteed "
            "ownership");
     ownershipKind = newKind;
@@ -8083,9 +8075,9 @@ class OwnershipForwardingTermInst : public TermInst,
   OwnershipForwardingTermInst(SILInstructionKind kind,
                               SILDebugLocation debugLoc,
                               ValueOwnershipKind ownershipKind,
-                              bool isDirectlyForwarding = true)
+                              bool preservesOwnership = true)
       : TermInst(kind, debugLoc),
-        OwnershipForwardingMixin(kind, ownershipKind, isDirectlyForwarding) {
+        OwnershipForwardingMixin(kind, ownershipKind, preservesOwnership) {
     assert(classof(kind));
   }
 
@@ -9062,16 +9054,12 @@ class CheckedCastBranchInst final
                         SILBasicBlock *SuccessBB, SILBasicBlock *FailureBB,
                         ProfileCounter Target1Count,
                         ProfileCounter Target2Count,
-                        ValueOwnershipKind forwardingOwnershipKind)
+                        ValueOwnershipKind forwardingOwnershipKind,
+                        bool preservesOwnership)
       : UnaryInstructionWithTypeDependentOperandsBase(
             DebugLoc, Operand, TypeDependentOperands, SuccessBB, FailureBB,
             Target1Count, Target2Count, forwardingOwnershipKind,
-            // We are always directly forwarding unless we are casting an
-            // AnyObject. This is b/c an AnyObject could contain a boxed
-            // AnyObject(Class()) that we unwrap as part of the cast. In such a
-            // case, we would return a different value and potentially end the
-            // lifetime of the operand value.
-            !Operand->getType().isAnyObject()),
+            preservesOwnership),
         DestLoweredTy(DestLoweredTy), DestFormalTy(DestFormalTy),
         IsExact(IsExact) {}
 

include/swift/SIL/TypeSubstCloner.h

@@ -269,8 +269,8 @@ class TypeSubstCloner : public SILClonerWithScopes<ImplClass> {
     auto FalseCount = inst->getFalseBBCount();
 
     // Try to use the scalar cast instruction.
-    if (canUseScalarCheckedCastInstructions(B.getModule(),
-                                            sourceType, targetType)) {
+    if (canSILUseScalarCheckedCastInstructions(B.getModule(),
+                                               sourceType, targetType)) {
       emitIndirectConditionalCastWithScalar(
           B, SwiftMod, loc, inst->getConsumptionKind(), src, sourceType, dest,
           targetType, succBB, failBB, TrueCount, FalseCount);

lib/AST/Type.cpp

@@ -978,6 +978,20 @@ bool TypeBase::isAnyObject() {
   return canTy.getExistentialLayout().isAnyObject();
 }
 
+// Distinguish between class-bound types that might be AnyObject vs other
+// class-bound types. Only types that are potentially AnyObject might have a
+// transparent runtime type wrapper like __SwiftValue. This must look through
+// all optional types because dynamic casting sees through them.
+bool TypeBase::isPotentiallyAnyObject() {
+  Type unwrappedTy = lookThroughAllOptionalTypes();
+  if (auto archetype = unwrappedTy->getAs<ArchetypeType>()) {
+    // Does archetype have any requirements that contradict AnyObject?
+    // 'T : AnyObject' requires a layout constraint, not a conformance.
+    return archetype->getConformsTo().empty() && !archetype->getSuperclass();
+  }
+  return unwrappedTy->isAnyObject();
+}
+
 bool ExistentialLayout::isErrorExistential() const {
   auto protocols = getProtocols();
   return (!hasExplicitAnyObject &&

lib/SIL/IR/SILInstructions.cpp

@@ -19,6 +19,7 @@
 #include "swift/Basic/AssertImplements.h"
 #include "swift/Basic/Unicode.h"
 #include "swift/Basic/type_traits.h"
+#include "swift/SIL/DynamicCasts.h"
 #include "swift/SIL/FormalLinkage.h"
 #include "swift/SIL/Projection.h"
 #include "swift/SIL/SILBuilder.h"
@@ -2283,16 +2284,18 @@ CheckedCastBranchInst *CheckedCastBranchInst::create(
     SILBasicBlock *FailureBB, SILFunction &F,
     ProfileCounter Target1Count, ProfileCounter Target2Count,
     ValueOwnershipKind forwardingOwnershipKind) {
-  SILModule &Mod = F.getModule();
+  SILModule &module = F.getModule();
+  bool preservesOwnership = doesCastPreserveOwnershipForTypes(
+    module, Operand->getType().getASTType(), DestFormalTy);
   SmallVector<SILValue, 8> TypeDependentOperands;
   collectTypeDependentOperands(TypeDependentOperands, F, DestFormalTy);
   unsigned size =
       totalSizeToAlloc<swift::Operand>(1 + TypeDependentOperands.size());
-  void *Buffer = Mod.allocateInst(size, alignof(CheckedCastBranchInst));
+  void *Buffer = module.allocateInst(size, alignof(CheckedCastBranchInst));
   return ::new (Buffer) CheckedCastBranchInst(
       DebugLoc, IsExact, Operand, TypeDependentOperands, DestLoweredTy,
       DestFormalTy, SuccessBB, FailureBB, Target1Count, Target2Count,
-      forwardingOwnershipKind);
+      forwardingOwnershipKind, preservesOwnership);
 }
 
 MetatypeInst *MetatypeInst::create(SILDebugLocation Loc, SILType Ty,