Implement basic support for [weak].

Swift SVN r7041

include/swift/AST/Diagnostics.def

@@ -386,6 +386,11 @@ ERROR(sil_expected_allocation_kind,decl_parsing,none,
       "expected allocation kind (heap, pseudo, or stack)", ())
 ERROR(sil_invalid_instr_operands,decl_parsing,none,
       "invalid instruction operands", ())
+ERROR(sil_operand_not_address,decl_parsing,none,
+      "%0 operand of '%1' must have address type", (StringRef, StringRef))
+ERROR(sil_operand_not_weak_address,decl_parsing,none,
+      "%0 operand of '%1' must have address of [weak] type",
+      (StringRef, StringRef))
 ERROR(sil_integer_literal_not_integer_type,decl_parsing,none,
       "integer_literal instruction requires a 'Builtin.Int<n>' type", ())
 ERROR(sil_float_literal_not_float_type,decl_parsing,none,

include/swift/Runtime/Alloc.h

@@ -268,7 +268,29 @@ struct WeakReference {
 /// Initialize a weak reference.
 ///
 /// \param ref - never null
-extern "C" void swift_weakInit(WeakReference *ref);
+/// \param value - can be null
+extern "C" void swift_weakInit(WeakReference *ref, HeapObject *value);
+
+/// Assign a new value to a weak reference.
+///
+/// \param ref - never null
+/// \param value - can be null
+extern "C" void swift_weakAssign(WeakReference *ref, HeapObject *value);
+
+/// Load a value from a weak reference.  If the current value is a
+/// non-null object that has begun deallocation, returns null;
+/// otherwise, retains the object before returning.
+///
+/// \param ref - never null
+/// \return can be null
+extern "C" HeapObject *swift_weakLoadStrong(WeakReference *ref);
+
+/// Load a value from a weak reference as if by swift_weakLoadStrong,
+/// but leaving the reference in an uninitialized state.
+///
+/// \param ref - never null
+/// \return can be null
+extern "C" HeapObject *swift_weakTakeStrong(WeakReference *ref);
 
 /// Destroy a weak reference.
 ///
@@ -299,11 +321,6 @@ extern "C" void swift_weakCopyAssign(WeakReference *dest, WeakReference *src);
 /// \param src - never null, but can refer to a null object
 extern "C" void swift_weakTakeAssign(WeakReference *dest, WeakReference *src);
 
-/// Try to retain a weak reference
-///
-/// \param object - never null, but can refer to a null object
-extern "C" HeapObject *swift_weakTryRetain(WeakReference *object);
-
 #if SWIFT_OBJC_INTEROP
 
 /// Increment the strong retain count of an object which may have been
@@ -318,6 +335,33 @@ extern "C" void swift_unknownWeakRetain(void *value);
 /// a native Swift object.
 extern "C" void swift_unknownWeakRelease(void *value);
 
+/// Initialize a weak reference.
+///
+/// \param ref - never null
+/// \param value - not necessarily a native Swift object; can be null
+extern "C" void swift_unknownWeakInit(WeakReference *ref, void *value);
+
+/// Assign a new value to a weak reference.
+///
+/// \param ref - never null
+/// \param value - not necessarily a native Swift object; can be null
+extern "C" void swift_unknownWeakAssign(WeakReference *ref, void *value);
+
+/// Load a value from a weak reference, much like swift_weakLoadStrong
+/// but without requiring the variable to refer to a native Swift object.
+///
+/// \param ref - never null
+/// \return can be null
+extern "C" void *swift_unknownWeakLoadStrong(WeakReference *ref);
+
+/// Load a value from a weak reference as if by
+/// swift_unknownWeakLoadStrong, but leaving the reference in an
+/// uninitialized state.
+///
+/// \param ref - never null
+/// \return can be null
+extern "C" void *swift_unknownWeakTakeStrong(WeakReference *ref);
+
 /// Destroy a weak reference variable that might not refer to a native
 /// Swift object.
 extern "C" void swift_unknownWeakDestroy(WeakReference *object);

include/swift/SIL/SILBuilder.h

@@ -222,6 +222,15 @@ public:
                     StoreInst(Loc, Src, DestLValue));
   }
 
+  LoadWeakInst *createLoadWeak(SILLocation loc, SILValue src, IsTake_t isTake) {
+    return insert(new (F.getModule()) LoadWeakInst(loc, src, isTake));
+  }
+
+  StoreWeakInst *createStoreWeak(SILLocation loc, SILValue value,
+                                 SILValue dest, IsInitialization_t isInit) {
+    return insert(new (F.getModule()) StoreWeakInst(loc, value, dest, isInit));
+  }
+
   InitializeVarInst *createInitializeVar(SILLocation Loc,
                                          SILValue DestLValue,
                                          bool canDefaultConstruct) {

include/swift/SIL/SILInstruction.h

@@ -53,6 +53,9 @@ enum class SILInstructionMemoryBehavior {
   MayWriteAndHaveSideEffects
 };
 
+enum IsTake_t { IsNotTake, IsTake };
+enum IsInitialization_t { IsNotInitialization, IsInitialization };
+
 /// This is the root class for all instructions that can be used as the contents
 /// of a Swift SILBasicBlock.
 class SILInstruction : public ValueBase,public llvm::ilist_node<SILInstruction>{
@@ -549,6 +552,53 @@ public:
   }
 };
 
+/// Represents a load from a [weak] memory location.
+class LoadWeakInst
+  : public UnaryInstructionBase<ValueKind::LoadWeakInst>
+{
+  static SILType getResultType(SILType operandTy) {
+    assert(operandTy.isAddress() && "loading from non-address operand?");
+    auto refType = cast<ReferenceStorageType>(operandTy.getSwiftRValueType());
+    return SILType::getPrimitiveObjectType(refType.getReferentType());
+  }
+
+  unsigned IsTake : 1; // FIXME: pack this somewhere
+
+public:
+  /// \param loc The location of the expression that caused the load.
+  /// \param lvalue The SILValue representing the address to
+  ///        use for the load.
+  LoadWeakInst(SILLocation loc, SILValue lvalue, IsTake_t isTake)
+    : UnaryInstructionBase(loc, lvalue, getResultType(lvalue.getType())),
+      IsTake(unsigned(isTake))
+  {}
+
+  IsTake_t isTake() const { return IsTake_t(IsTake); }
+};
+
+/// Represents a store to a [weak] memory location.
+class StoreWeakInst : public SILInstruction {
+  enum { Src, Dest };
+  FixedOperandList<2> Operands;
+  unsigned IsInit : 1; // FIXME: pack this somewhere
+public:
+  StoreWeakInst(SILLocation loc, SILValue src, SILValue dest,
+                IsInitialization_t isInit);
+
+  SILValue getSrc() const { return Operands[Src].get(); }
+  SILValue getDest() const { return Operands[Dest].get(); }
+
+  IsInitialization_t isInitialization() const {
+    return IsInitialization_t(IsInit);
+  }
+
+  ArrayRef<Operand> getAllOperands() const { return Operands.asArray(); }
+
+  static bool classof(const ValueBase *V) {
+    return V->getKind() == ValueKind::StoreWeakInst;
+  }
+};
+
 /// InitializeVarInst - Represents a default initialization of a variable.
 class InitializeVarInst
   : public UnaryInstructionBase<ValueKind::InitializeVarInst,
@@ -566,9 +616,6 @@ public:
   bool canDefaultConstruct() const { return CanDefaultConstruct; }
 };
 
-enum IsTake_t { IsNotTake, IsTake };
-enum IsInitialization_t { IsNotInitialization, IsInitialization };
-
 /// CopyAddrInst - Represents a copy from one memory location to another. This
 /// is similar to:
 ///   %1 = load %src

include/swift/SIL/SILNodes.def

@@ -72,7 +72,9 @@ ABSTRACT_VALUE(SILInstruction, ValueBase)
 
   // Accessing memory
   INST(LoadInst, SILInstruction, None)
+  INST(LoadWeakInst, SILInstruction, None)
   INST(StoreInst, SILInstruction, MayWrite)
+  INST(StoreWeakInst, SILInstruction, MayWrite)
   INST(InitializeVarInst, SILInstruction, MayWrite)
   INST(CopyAddrInst, SILInstruction, MayWrite)
   INST(DestroyAddrInst, SILInstruction, MayHaveSideEffects)

lib/IRGen/GenHeap.cpp

@@ -606,34 +606,60 @@ namespace {
   class SwiftWeakReferenceTypeInfo
     : public IndirectTypeInfo<SwiftWeakReferenceTypeInfo,
                               WeakTypeInfo> {
+    llvm::Type *ValueType;
   public:
-    SwiftWeakReferenceTypeInfo(llvm::Type *type,
+    SwiftWeakReferenceTypeInfo(llvm::Type *valueType,
+                               llvm::Type *weakType,
                                Size size, Alignment alignment)
-      : IndirectTypeInfo(type, size, alignment) {}
+      : IndirectTypeInfo(weakType, size, alignment), ValueType(valueType) {}
 
     void initializeWithCopy(IRGenFunction &IGF, Address destAddr,
-                            Address srcAddr) const {
+                            Address srcAddr) const override {
       IGF.emitWeakCopyInit(destAddr, srcAddr);
     }
 
     void initializeWithTake(IRGenFunction &IGF, Address destAddr,
-                            Address srcAddr) const {
+                            Address srcAddr) const override {
       IGF.emitWeakTakeInit(destAddr, srcAddr);
     }
 
     void assignWithCopy(IRGenFunction &IGF, Address destAddr,
-                        Address srcAddr) const {
+                        Address srcAddr) const override {
       IGF.emitWeakCopyAssign(destAddr, srcAddr);
     }
 
     void assignWithTake(IRGenFunction &IGF, Address destAddr,
-                        Address srcAddr) const {
+                        Address srcAddr) const override {
       IGF.emitWeakTakeAssign(destAddr, srcAddr);
     }
 
-    void destroy(IRGenFunction &IGF, Address addr) const {
+    void destroy(IRGenFunction &IGF, Address addr) const override {
       IGF.emitWeakDestroy(addr);
     }
+
+    void weakLoadStrong(IRGenFunction &IGF, Address addr,
+                        Explosion &out) const override {
+      out.add(IGF.emitWeakLoadStrong(addr, ValueType));
+    }
+
+    void weakTakeStrong(IRGenFunction &IGF, Address addr,
+                        Explosion &out) const override {
+      out.add(IGF.emitWeakTakeStrong(addr, ValueType));
+    }
+
+    void weakInit(IRGenFunction &IGF, Explosion &in,
+                  Address dest) const override {
+      llvm::Value *value = in.claimNext();
+      assert(value->getType() == ValueType);
+      IGF.emitWeakInit(value, dest);
+    }
+
+    void weakAssign(IRGenFunction &IGF, Explosion &in,
+                    Address dest) const override {
+      llvm::Value *value = in.claimNext();
+      assert(value->getType() == ValueType);
+      IGF.emitWeakAssign(value, dest);
+    }
   };
 }
 
@@ -646,7 +672,8 @@ TypeConverter::createSwiftUnownedStorageType(llvm::Type *valueType) {
 
 const WeakTypeInfo *
 TypeConverter::createSwiftWeakStorageType(llvm::Type *valueType) {
-  return new SwiftWeakReferenceTypeInfo(IGM.WeakReferencePtrTy,
+  return new SwiftWeakReferenceTypeInfo(valueType,
+                                    IGM.WeakReferencePtrTy->getElementType(),
                                         IGM.getWeakReferenceSize(),
                                         IGM.getWeakReferenceAlignment());
 }
@@ -678,10 +705,14 @@ namespace {
   class UnknownWeakReferenceTypeInfo :
       public IndirectTypeInfo<UnknownWeakReferenceTypeInfo,
                               WeakTypeInfo> {
+    /// We need to separately store the value type because we always
+    /// use the same type to store the weak reference struct.
+    llvm::Type *ValueType;
   public:
-    UnknownWeakReferenceTypeInfo(llvm::Type *type,
+    UnknownWeakReferenceTypeInfo(llvm::Type *valueType,
+                                 llvm::Type *weakType,
                                  Size size, Alignment alignment)
-      : IndirectTypeInfo(type, size, alignment) {}
+      : IndirectTypeInfo(weakType, size, alignment), ValueType(valueType) {}
 
     void initializeWithCopy(IRGenFunction &IGF, Address destAddr,
                             Address srcAddr) const {
@@ -706,6 +737,30 @@ namespace {
     void destroy(IRGenFunction &IGF, Address addr) const {
       IGF.emitUnknownWeakDestroy(addr);
     }
+
+    void weakLoadStrong(IRGenFunction &IGF, Address addr,
+                        Explosion &out) const override {
+      out.add(IGF.emitUnknownWeakLoadStrong(addr, ValueType));
+    }
+
+    void weakTakeStrong(IRGenFunction &IGF, Address addr,
+                        Explosion &out) const override {
+      out.add(IGF.emitUnknownWeakTakeStrong(addr, ValueType));
+    }
+
+    void weakInit(IRGenFunction &IGF, Explosion &in,
+                  Address dest) const override {
+      llvm::Value *value = in.claimNext();
+      assert(value->getType() == ValueType);
+      IGF.emitUnknownWeakInit(value, dest);
+    }
+
+    void weakAssign(IRGenFunction &IGF, Explosion &in,
+                    Address dest) const override {
+      llvm::Value *value = in.claimNext();
+      assert(value->getType() == ValueType);
+      IGF.emitUnknownWeakAssign(value, dest);
+    }
   };
 }
 
@@ -718,7 +773,8 @@ TypeConverter::createUnknownUnownedStorageType(llvm::Type *valueType) {
 
 const WeakTypeInfo *
 TypeConverter::createUnknownWeakStorageType(llvm::Type *valueType) {
-  return new UnknownWeakReferenceTypeInfo(IGM.WeakReferencePtrTy,
+  return new UnknownWeakReferenceTypeInfo(valueType,
+                                      IGM.WeakReferencePtrTy->getElementType(),
                                           IGM.getWeakReferenceSize(),
                                           IGM.getWeakReferenceAlignment());
 }
@@ -729,17 +785,19 @@ static bool doesNotRequireRefCounting(llvm::Value *value) {
   return isa<llvm::Constant>(value);
 }
 
+static llvm::FunctionType *getTypeOfFunction(llvm::Constant *fn) {
+  return cast<llvm::FunctionType>(fn->getType()->getPointerElementType());
+}
+
 /// Emit a unary call to perform a ref-counting operation.
 ///
-/// \param fn - expected signature 'void (T*)'
+/// \param fn - expected signature 'void (T)'
 static void emitUnaryRefCountCall(IRGenFunction &IGF,
                                   llvm::Constant *fn,
                                   llvm::Value *value) {
-  auto fnTy = cast<llvm::FunctionType>(fn->getType()->getPointerElementType());
+  // Instead of casting the input, we cast the function type.
-
+  // This tends to produce less IR, but might be evil.
-  // Instead of casting the input to %swift.refcounted*, we cast the
+  if (value->getType() != getTypeOfFunction(fn)->getParamType(0)) {
-  // function type.  This tends to produce less IR, but might be evil.
-  if (value->getType() != fnTy->getParamType(0)) {
     llvm::FunctionType *fnType =
       llvm::FunctionType::get(IGF.IGM.VoidTy, value->getType(), false);
     fn = llvm::ConstantExpr::getBitCast(fn, fnType->getPointerTo());
@@ -751,20 +809,19 @@ static void emitUnaryRefCountCall(IRGenFunction &IGF,
   call->setDoesNotThrow();  
 }
 
-/// Emit a unary call to perform a ref-counting operation.
+/// Emit a copy-like call to perform a ref-counting operation.
 ///
-/// \param fn - expected signature 'void (T*, T*)'
+/// \param fn - expected signature 'void (T, T)'
-static void emitBinaryRefCountCall(IRGenFunction &IGF,
+static void emitCopyLikeCall(IRGenFunction &IGF,
-                                   llvm::Constant *fn,
+                             llvm::Constant *fn,
-                                   llvm::Value *dest,
+                             llvm::Value *dest,
-                                   llvm::Value *src) {
+                             llvm::Value *src) {
   assert(dest->getType() == src->getType() &&
          "type mismatch in binary refcounting operation");
 
-  // Instead of casting the input to %swift.refcounted*, we cast the
+  // Instead of casting the inputs, we cast the function type.
-  // function type.  This tends to produce less IR, but might be evil.
+  // This tends to produce less IR, but might be evil.
-  if (dest->getType() !=
+  if (dest->getType() != getTypeOfFunction(fn)->getParamType(0)) {
-        cast<llvm::FunctionType>(fn->getType())->getParamType(0)) {
     llvm::Type *paramTypes[] = { dest->getType(), dest->getType() };
     llvm::FunctionType *fnType =
       llvm::FunctionType::get(IGF.IGM.VoidTy, paramTypes, false);
@@ -777,6 +834,58 @@ static void emitBinaryRefCountCall(IRGenFunction &IGF,
   call->setDoesNotThrow();  
 }
 
+/// Emit a call to a function with a loadWeak-like signature.
+///
+/// \param fn - expected signature 'T (Weak*)'
+static llvm::Value *emitLoadWeakLikeCall(IRGenFunction &IGF,
+                                         llvm::Constant *fn,
+                                         llvm::Value *addr,
+                                         llvm::Type *resultType) {
+  assert(addr->getType() == IGF.IGM.WeakReferencePtrTy &&
+         "address is not of a weak reference");
+
+  // Instead of casting the output, we cast the function type.
+  // This tends to produce less IR, but might be evil.
+  if (resultType != getTypeOfFunction(fn)->getReturnType()) {
+    llvm::Type *paramTypes[] = { addr->getType() };
+    llvm::FunctionType *fnType =
+      llvm::FunctionType::get(resultType, paramTypes, false);
+    fn = llvm::ConstantExpr::getBitCast(fn, fnType->getPointerTo());
+  }
+
+  // Emit the call.
+  llvm::CallInst *call = IGF.Builder.CreateCall(fn, addr);
+  call->setCallingConv(IGF.IGM.RuntimeCC);
+  call->setDoesNotThrow();
+
+  return call;
+}
+
+/// Emit a call to a function with a storeWeak-like signature.
+///
+/// \param fn - expected signature 'void (Weak*, T)'
+static void emitStoreWeakLikeCall(IRGenFunction &IGF,
+                                  llvm::Constant *fn,
+                                  llvm::Value *addr,
+                                  llvm::Value *value) {
+  assert(addr->getType() == IGF.IGM.WeakReferencePtrTy &&
+         "address is not of a weak reference");
+
+  // Instead of casting the inputs, we cast the function type.
+  // This tends to produce less IR, but might be evil.
+  if (value->getType() != getTypeOfFunction(fn)->getParamType(1)) {
+    llvm::Type *paramTypes[] = { addr->getType(), value->getType() };
+    llvm::FunctionType *fnType =
+      llvm::FunctionType::get(IGF.IGM.VoidTy, paramTypes, false);
+    fn = llvm::ConstantExpr::getBitCast(fn, fnType->getPointerTo());
+  }
+
+  // Emit the call.
+  llvm::CallInst *call = IGF.Builder.CreateCall2(fn, addr, value);
+  call->setCallingConv(IGF.IGM.RuntimeCC);
+  call->setDoesNotThrow();
+}
+
 /// Emit a call to swift_retain_noresult.  In general, you should not be using
 /// this routine; instead you should use emitRetain, which properly
 /// balances the retain.
@@ -856,34 +965,52 @@ void IRGenFunction::emitUnknownRelease(llvm::Value *value) {
   return emitObjCRelease(value);
 }
 
-#define REFCOUNT_VALUE(ID)                                            \
+#define DEFINE_VALUE_OP(ID)                                           \
 void IRGenFunction::emit##ID(llvm::Value *value) {                    \
   if (doesNotRequireRefCounting(value)) return;                       \
   emitUnaryRefCountCall(*this, IGM.get##ID##Fn(), value);             \
 }
-#define REFCOUNT_ADDR(ID)                                             \
+#define DEFINE_ADDR_OP(ID)                                            \
 void IRGenFunction::emit##ID(Address addr) {                          \
   emitUnaryRefCountCall(*this, IGM.get##ID##Fn(), addr.getAddress()); \
 }
-#define REFCOUNT_ADDR_ADDR(ID)                                        \
+#define DEFINE_COPY_OP(ID)                                            \
 void IRGenFunction::emit##ID(Address dest, Address src) {             \
-  emitBinaryRefCountCall(*this, IGM.get##ID##Fn(), dest.getAddress(), \
+  emitCopyLikeCall(*this, IGM.get##ID##Fn(), dest.getAddress(),       \
-                         src.getAddress());                           \
+                   src.getAddress());                                 \
+}
+#define DEFINE_LOAD_WEAK_OP(ID)                                       \
+llvm::Value *IRGenFunction::emit##ID(Address src, llvm::Type *type) { \
+  return emitLoadWeakLikeCall(*this, IGM.get##ID##Fn(),               \
+                              src.getAddress(), type);                \
+}
+#define DEFINE_STORE_WEAK_OP(ID)                                      \
+void IRGenFunction::emit##ID(llvm::Value *value, Address src) {       \
+  emitStoreWeakLikeCall(*this, IGM.get##ID##Fn(),                     \
+                        src.getAddress(), value);                     \
 }
 
-REFCOUNT_VALUE(RetainUnowned)
+DEFINE_VALUE_OP(RetainUnowned)
-REFCOUNT_VALUE(UnownedRelease)
+DEFINE_VALUE_OP(UnownedRelease)
-REFCOUNT_VALUE(UnownedRetain)
+DEFINE_VALUE_OP(UnownedRetain)
-REFCOUNT_ADDR(WeakDestroy)
+DEFINE_LOAD_WEAK_OP(WeakLoadStrong)
-REFCOUNT_ADDR_ADDR(WeakCopyInit)
+DEFINE_LOAD_WEAK_OP(WeakTakeStrong)
-REFCOUNT_ADDR_ADDR(WeakCopyAssign)
+DEFINE_STORE_WEAK_OP(WeakInit)
-REFCOUNT_ADDR_ADDR(WeakTakeInit)
+DEFINE_STORE_WEAK_OP(WeakAssign)
-REFCOUNT_ADDR_ADDR(WeakTakeAssign)
+DEFINE_ADDR_OP(WeakDestroy)
-REFCOUNT_VALUE(UnknownRetainUnowned)
+DEFINE_COPY_OP(WeakCopyInit)
-REFCOUNT_VALUE(UnknownUnownedRelease)
+DEFINE_COPY_OP(WeakCopyAssign)
-REFCOUNT_VALUE(UnknownUnownedRetain)
+DEFINE_COPY_OP(WeakTakeInit)
-REFCOUNT_ADDR(UnknownWeakDestroy)
+DEFINE_COPY_OP(WeakTakeAssign)
-REFCOUNT_ADDR_ADDR(UnknownWeakCopyInit)
+DEFINE_VALUE_OP(UnknownRetainUnowned)
-REFCOUNT_ADDR_ADDR(UnknownWeakCopyAssign)
+DEFINE_VALUE_OP(UnknownUnownedRelease)
-REFCOUNT_ADDR_ADDR(UnknownWeakTakeInit)
+DEFINE_VALUE_OP(UnknownUnownedRetain)
-REFCOUNT_ADDR_ADDR(UnknownWeakTakeAssign)
+DEFINE_LOAD_WEAK_OP(UnknownWeakLoadStrong)
+DEFINE_LOAD_WEAK_OP(UnknownWeakTakeStrong)
+DEFINE_STORE_WEAK_OP(UnknownWeakInit)
+DEFINE_STORE_WEAK_OP(UnknownWeakAssign)
+DEFINE_ADDR_OP(UnknownWeakDestroy)
+DEFINE_COPY_OP(UnknownWeakCopyInit)
+DEFINE_COPY_OP(UnknownWeakCopyAssign)
+DEFINE_COPY_OP(UnknownWeakTakeInit)
+DEFINE_COPY_OP(UnknownWeakTakeAssign)

lib/IRGen/GenProto.cpp

@@ -561,6 +561,24 @@ namespace {
       IGF.emitMemCpy(dest, src, NumProtocols * IGF.IGM.getPointerSize());
     }
 
+    void emitLoadOfTables(IRGenFunction &IGF, Address existential,
+                          Explosion &out) const {
+      for (unsigned i = 0; i != NumProtocols; ++i) {
+        auto tableAddr = IGF.Builder.CreateStructGEP(existential, i,
+                                                i * IGF.IGM.getPointerSize());
+        out.add(IGF.Builder.CreateLoad(tableAddr));
+      }
+    }
+
+    void emitStoreOfTables(IRGenFunction &IGF, Explosion &in,
+                           Address existential) const {
+      for (unsigned i = 0; i != NumProtocols; ++i) {
+        auto tableAddr = IGF.Builder.CreateStructGEP(existential, i,
+                                                i * IGF.IGM.getPointerSize());
+        IGF.Builder.CreateStore(in.claimNext(), tableAddr);
+      }
+    }
+
     Address projectValue(IRGenFunction &IGF, Address existential) const {
       return IGF.Builder.CreateStructGEP(existential, NumProtocols,
                                        NumProtocols * IGF.IGM.getPointerSize(),
@@ -602,6 +620,43 @@ namespace {
       Address valueAddr = projectValue(IGF, existential);
       IGF.emitUnknownWeakDestroy(valueAddr);
     }
+
+    // These explosions must follow the same schema as
+    // ClassExistentialTypeInfo, i.e. first the tables, then the value.
+
+    void weakLoadStrong(IRGenFunction &IGF, Address existential,
+                        Explosion &out) const override {
+      emitLoadOfTables(IGF, existential, out);
+      Address valueAddr = projectValue(IGF, existential);
+      out.add(IGF.emitUnknownWeakLoadStrong(valueAddr,
+                                            IGF.IGM.UnknownRefCountedPtrTy));
+    }
+
+    void weakTakeStrong(IRGenFunction &IGF, Address existential,
+                        Explosion &out) const override {
+      emitLoadOfTables(IGF, existential, out);
+      Address valueAddr = projectValue(IGF, existential);
+      out.add(IGF.emitUnknownWeakTakeStrong(valueAddr,
+                                            IGF.IGM.UnknownRefCountedPtrTy));
+    }
+
+    void weakInit(IRGenFunction &IGF, Explosion &in,
+                  Address existential) const override {
+      emitStoreOfTables(IGF, in, existential);
+      llvm::Value *value = in.claimNext();
+      assert(value->getType() == IGF.IGM.UnknownRefCountedPtrTy);
+      Address valueAddr = projectValue(IGF, existential);
+      IGF.emitUnknownWeakInit(value, valueAddr);
+    }
+
+    void weakAssign(IRGenFunction &IGF, Explosion &in,
+                    Address existential) const override {
+      emitStoreOfTables(IGF, in, existential);
+      llvm::Value *value = in.claimNext();
+      assert(value->getType() == IGF.IGM.UnknownRefCountedPtrTy);
+      Address valueAddr = projectValue(IGF, existential);
+      IGF.emitUnknownWeakAssign(value, valueAddr);
+    }
   };
 
   /// A helper class for working with existential types that can be

lib/IRGen/IRGenFunction.h

@@ -169,7 +169,10 @@ public:
   void emitRetainUnowned(llvm::Value *value);
   void emitUnownedRetain(llvm::Value *value);
   void emitUnownedRelease(llvm::Value *value);
-  void emitWeakInit(Address addr);
+  void emitWeakInit(llvm::Value *value, Address dest);
+  void emitWeakAssign(llvm::Value *value, Address dest);
+  llvm::Value *emitWeakLoadStrong(Address src, llvm::Type *type);
+  llvm::Value *emitWeakTakeStrong(Address src, llvm::Type *type);
   void emitWeakDestroy(Address addr);
   void emitWeakCopyInit(Address destAddr, Address srcAddr);
   void emitWeakTakeInit(Address destAddr, Address srcAddr);
@@ -194,6 +197,10 @@ public:
   void emitUnknownWeakTakeInit(Address destAddr, Address srcAddr);
   void emitUnknownWeakCopyAssign(Address destAddr, Address srcAddr);
   void emitUnknownWeakTakeAssign(Address destAddr, Address srcAddr);
+  void emitUnknownWeakInit(llvm::Value *value, Address dest);
+  void emitUnknownWeakAssign(llvm::Value *value, Address dest);
+  llvm::Value *emitUnknownWeakLoadStrong(Address src, llvm::Type *type);
+  llvm::Value *emitUnknownWeakTakeStrong(Address src, llvm::Type *type);
 
 //--- Expression emission ------------------------------------------------------
 public:

lib/IRGen/IRGenSIL.cpp

@@ -49,6 +49,7 @@
 #include "IRGenModule.h"
 #include "Linking.h"
 #include "ReferenceTypeInfo.h"
+#include "WeakTypeInfo.h"
 
 using namespace swift;
 using namespace irgen;
@@ -508,6 +509,8 @@ public:
 
   void visitLoadInst(LoadInst *i);
   void visitStoreInst(StoreInst *i);
+  void visitLoadWeakInst(LoadWeakInst *i);
+  void visitStoreWeakInst(StoreWeakInst *i);
   void visitStructInst(StructInst *i);
   void visitTupleInst(TupleInst *i);
   void visitBuiltinZeroInst(BuiltinZeroInst *i);
@@ -1674,6 +1677,33 @@ void IRGenSILFunction::visitStoreInst(swift::StoreInst *i) {
   type.initialize(*this, source, dest);
 }
 
+void IRGenSILFunction::visitLoadWeakInst(swift::LoadWeakInst *i) {
+  Address source = getLoweredAddress(i->getOperand());
+  auto &weakTI =
+    cast<WeakTypeInfo>(getFragileTypeInfo(i->getOperand().getType()));
+
+  Explosion result(ExplosionKind::Maximal);
+  if (i->isTake()) {
+    weakTI.weakTakeStrong(*this, source, result);
+  } else {
+    weakTI.weakLoadStrong(*this, source, result);
+  }
+
+  setLoweredExplosion(SILValue(i, 0), result);
+}
+
+void IRGenSILFunction::visitStoreWeakInst(swift::StoreWeakInst *i) {
+  Explosion source = getLoweredExplosion(i->getSrc());
+  Address dest = getLoweredAddress(i->getDest());
+
+  auto &weakTI = cast<WeakTypeInfo>(getFragileTypeInfo(i->getDest().getType()));
+  if (i->isInitialization()) {
+    weakTI.weakInit(*this, source, dest);
+  } else {
+    weakTI.weakAssign(*this, source, dest);
+  }
+}
+
 void IRGenSILFunction::visitRetainInst(swift::RetainInst *i) {
   // FIXME: Specialization thunks may eventually require retaining. For now,
   // since we don't yet thunk specialized function values, ignore retains

lib/IRGen/RuntimeFunctions.def

@@ -116,31 +116,55 @@ FUNCTION(UnownedRelease, swift_weakRelease,RuntimeCC,
          ARGS(RefCountedPtrTy),
          ATTRS(NoUnwind))
 
-// void swift_weakDestroy(void **object);
+// void swift_weakDestroy(WeakReference *object);
 FUNCTION(WeakDestroy,    swift_weakDestroy,   RuntimeCC,
          RETURNS(VoidTy),
          ARGS(WeakReferencePtrTy),
          ATTRS(NoUnwind))
 
-// void swift_weakCopyInit(void **dest, void **src);
+// void swift_weakInit(WeakReference *object, void *value);
+FUNCTION(WeakInit,       swift_weakInit,      RuntimeCC,
+         RETURNS(VoidTy),
+         ARGS(WeakReferencePtrTy, RefCountedPtrTy),
+         ATTRS(NoUnwind))
+
+// void swift_weakAssign(WeakReference *object, void *value);
+FUNCTION(WeakAssign,     swift_weakAssign,    RuntimeCC,
+         RETURNS(VoidTy),
+         ARGS(WeakReferencePtrTy, RefCountedPtrTy),
+         ATTRS(NoUnwind))
+
+// void *swift_weakLoadStrong(WeakReference *object);
+FUNCTION(WeakLoadStrong, swift_weakLoadStrong,RuntimeCC,
+         RETURNS(RefCountedPtrTy),
+         ARGS(WeakReferencePtrTy),
+         ATTRS(NoUnwind))
+
+// void *swift_weakTakeStrong(WeakReference *object);
+FUNCTION(WeakTakeStrong, swift_weakTakeStrong,RuntimeCC,
+         RETURNS(RefCountedPtrTy),
+         ARGS(WeakReferencePtrTy),
+         ATTRS(NoUnwind))
+
+// void swift_weakCopyInit(WeakReference *dest, WeakReference *src);
 FUNCTION(WeakCopyInit,   swift_weakCopyInit,  RuntimeCC,
          RETURNS(VoidTy),
          ARGS(WeakReferencePtrTy, WeakReferencePtrTy),
          ATTRS(NoUnwind))
 
-// void swift_weakTakeInit(void **dest, void **src);
+// void swift_weakTakeInit(WeakReference *dest, WeakReference *src);
 FUNCTION(WeakTakeInit,   swift_weakTakeInit,  RuntimeCC,
          RETURNS(VoidTy),
          ARGS(WeakReferencePtrTy, WeakReferencePtrTy),
          ATTRS(NoUnwind))
 
-// void swift_weakCopyAssign(void **dest, void **src);
+// void swift_weakCopyAssign(WeakReference *dest, WeakReference *src);
 FUNCTION(WeakCopyAssign, swift_weakCopyAssign,RuntimeCC,
          RETURNS(VoidTy),
          ARGS(WeakReferencePtrTy, WeakReferencePtrTy),
          ATTRS(NoUnwind))
 
-// void swift_weakTakeAssign(void **dest, void **src);
+// void swift_weakTakeAssign(WeakReference *dest, WeakReference *src);
 FUNCTION(WeakTakeAssign, swift_weakTakeAssign,RuntimeCC,
          RETURNS(VoidTy),
          ARGS(WeakReferencePtrTy, WeakReferencePtrTy),
@@ -164,31 +188,55 @@ FUNCTION(UnknownUnownedRelease, swift_unknownWeakRelease,   RuntimeCC,
          ARGS(RefCountedPtrTy),
          ATTRS(NoUnwind))
 
-// void swift_unknownWeakDestroy(void **object);
+// void swift_unknownWeakDestroy(WeakReference *object);
 FUNCTION(UnknownWeakDestroy,    swift_unknownWeakDestroy,   RuntimeCC,
          RETURNS(VoidTy),
          ARGS(WeakReferencePtrTy),
          ATTRS(NoUnwind))
 
-// void swift_unknownWeakCopyInit(void **dest, void **src);
+// void swift_unknownWeakInit(WeakReference *object, void *value);
+FUNCTION(UnknownWeakInit,       swift_unknownWeakInit,      RuntimeCC,
+         RETURNS(VoidTy),
+         ARGS(WeakReferencePtrTy, UnknownRefCountedPtrTy),
+         ATTRS(NoUnwind))
+
+// void swift_unknownWeakAssign(WeakReference *object, void *value);
+FUNCTION(UnknownWeakAssign,     swift_unknownWeakAssign,    RuntimeCC,
+         RETURNS(VoidTy),
+         ARGS(WeakReferencePtrTy, UnknownRefCountedPtrTy),
+         ATTRS(NoUnwind))
+
+// void *swift_unknownWeakLoad(WeakReference *object);
+FUNCTION(UnknownWeakLoadStrong, swift_unknownWeakLoadStrong,RuntimeCC,
+         RETURNS(UnknownRefCountedPtrTy),
+         ARGS(WeakReferencePtrTy),
+         ATTRS(NoUnwind))
+
+// void *swift_unknownWeakTake(WeakReference *object);
+FUNCTION(UnknownWeakTakeStrong, swift_unknownWeakTakeStrong,RuntimeCC,
+         RETURNS(UnknownRefCountedPtrTy),
+         ARGS(WeakReferencePtrTy),
+         ATTRS(NoUnwind))
+
+// void swift_unknownWeakCopyInit(WeakReference *dest, WeakReference *src);
 FUNCTION(UnknownWeakCopyInit,   swift_unknownWeakCopyInit,  RuntimeCC,
          RETURNS(VoidTy),
          ARGS(WeakReferencePtrTy, WeakReferencePtrTy),
          ATTRS(NoUnwind))
 
-// void swift_unknownWeakTakeInit(void **dest, void **src);
+// void swift_unknownWeakTakeInit(WeakReference *dest, WeakReference *src);
 FUNCTION(UnknownWeakTakeInit,   swift_unknownWeakTakeInit,  RuntimeCC,
          RETURNS(VoidTy),
          ARGS(WeakReferencePtrTy, WeakReferencePtrTy),
          ATTRS(NoUnwind))
 
-// void swift_unknownWeakCopyAssign(void **dest, void **src);
+// void swift_unknownWeakCopyAssign(WeakReference *dest, WeakReference *src);
 FUNCTION(UnknownWeakCopyAssign, swift_unknownWeakCopyAssign,RuntimeCC,
          RETURNS(VoidTy),
          ARGS(WeakReferencePtrTy, WeakReferencePtrTy),
          ATTRS(NoUnwind))
 
-// void swift_unknownWeakTakeAssign(void **dest, void **src);
+// void swift_unknownWeakTakeAssign(WeakReference *dest, WeakReference *src);
 FUNCTION(UnknownWeakTakeAssign, swift_unknownWeakTakeAssign,RuntimeCC,
          RETURNS(VoidTy),
          ARGS(WeakReferencePtrTy, WeakReferencePtrTy),

lib/IRGen/WeakTypeInfo.h

@@ -31,6 +31,15 @@ protected:
     : FixedTypeInfo(type, size, align, IsNotPOD, STIK_Weak) {}
 
 public:
+  virtual void weakLoadStrong(IRGenFunction &IGF, Address addr,
+                              Explosion &out) const = 0;
+  virtual void weakTakeStrong(IRGenFunction &IGF, Address addr,
+                              Explosion &out) const = 0;
+  virtual void weakInit(IRGenFunction &IGF, Explosion &src,
+                        Address dest) const = 0;
+  virtual void weakAssign(IRGenFunction &IGF, Explosion &src,
+                          Address dest) const = 0;
+
   static bool classof(const WeakTypeInfo *type) { return true; }
   static bool classof(const TypeInfo *type) {
     return type->getSpecialTypeInfoKind() == STIK_Weak;

lib/Parse/ParseSIL.cpp

@@ -850,6 +850,7 @@ bool SILParser::parseSILOpcode(ValueKind &Opcode, SourceLoc &OpcodeLoc,
     .Case("is_nonnull", ValueKind::IsNonnullInst)
     .Case("function_ref", ValueKind::FunctionRefInst)
     .Case("load", ValueKind::LoadInst)
+    .Case("load_weak", ValueKind::LoadWeakInst)
     .Case("metatype", ValueKind::MetatypeInst)
     .Case("object_pointer_to_ref", ValueKind::ObjectPointerToRefInst)
     .Case("partial_apply", ValueKind::PartialApplyInst)
@@ -871,6 +872,7 @@ bool SILParser::parseSILOpcode(ValueKind &Opcode, SourceLoc &OpcodeLoc,
     .Case("retain_unowned", ValueKind::RetainUnownedInst)
     .Case("return", ValueKind::ReturnInst)
     .Case("store", ValueKind::StoreInst)
+    .Case("store_weak", ValueKind::StoreWeakInst)
     .Case("string_literal", ValueKind::StringLiteralInst)
     .Case("struct", ValueKind::StructInst)
     .Case("struct_element_addr", ValueKind::StructElementAddrInst)
@@ -1156,6 +1158,15 @@ bool SILParser::parseSILInstruction(SILBasicBlock *BB) {
     if (parseTypedValueRef(Val)) return true;
     ResultVal = B.createLoad(InstLoc, Val);
     break;
+  case ValueKind::LoadWeakInst: {
+    bool isTake = false;
+    if (parseSILOptional(isTake, P, "take") ||
+        parseTypedValueRef(Val))
+      return true;
+
+    ResultVal = B.createLoadWeak(SILLocation(), Val, IsTake_t(isTake));
+    break;
+  }
 
     // Conversion instructions.
   case ValueKind::RefToObjectPointerInst:
@@ -1299,30 +1310,48 @@ bool SILParser::parseSILInstruction(SILBasicBlock *BB) {
     break;
   }
 
-  case ValueKind::StoreInst: {
+  case ValueKind::StoreInst:
-    UnresolvedValueName From;
+  case ValueKind::StoreWeakInst: {
+    UnresolvedValueName from;
 
-    SourceLoc ToLoc, AddrLoc;
+    SourceLoc toLoc, addrLoc;
-    Identifier ToToken;
+    Identifier toToken;
-    SILValue AddrVal;
+    SILValue addrVal;
-    if (parseValueName(From) ||
+    bool isInit = false;
-        P.parseIdentifier(ToToken, ToLoc,
+    if (parseValueName(from) ||
+        P.parseIdentifier(toToken, toLoc,
                           diag::expected_tok_in_sil_instr, "to") ||
-        parseTypedValueRef(AddrVal, AddrLoc))
+        (Opcode == ValueKind::StoreWeakInst &&
+         parseSILOptional(isInit, P, "initialization")) ||
+        parseTypedValueRef(addrVal, addrLoc))
       return true;
 
-    if (ToToken.str() != "to") {
+    if (toToken.str() != "to") {
-      P.diagnose(ToLoc, diag::expected_tok_in_sil_instr, "to");
+      P.diagnose(toLoc, diag::expected_tok_in_sil_instr, "to");
       return true;
     }
 
-    if (!AddrVal.getType().isAddress()) {
+    if (!addrVal.getType().isAddress()) {
-      P.diagnose(AddrLoc, diag::sil_invalid_instr_operands);
+      P.diagnose(addrLoc, diag::sil_operand_not_address,
+                 "destination", OpcodeName);
       return true;
     }
 
-    SILValue FromVal = getLocalValue(From, AddrVal.getType().getObjectType());
+    SILType valueTy;
-    ResultVal = B.createStore(InstLoc, FromVal, AddrVal);
+    if (Opcode == ValueKind::StoreInst) {
+      valueTy = addrVal.getType().getObjectType();
+    } else {
+      auto refType = addrVal.getType().getAs<ReferenceStorageType>();
+      if (!refType || refType->getOwnership() != Ownership::Weak) {
+        P.diagnose(addrLoc, diag::sil_operand_not_weak_address,
+                   "destination", OpcodeName);
+        return true;
+      }
+      valueTy = SILType::getPrimitiveObjectType(refType.getReferentType());
+    }
+
+    SILValue fromVal = getLocalValue(from, valueTy);
+    ResultVal = B.createStore(InstLoc, fromVal, addrVal);
     break;
   }
   case ValueKind::AllocStackInst:

lib/SIL/SILGen/SILGenExpr.cpp

@@ -357,7 +357,7 @@ ManagedValue SILGenFunction::emitLoad(SILLocation loc,
                                       IsTake_t isTake) {
   auto &addrTL = getTypeLowering(addr.getType());
   auto &semanticTL = addrTL.getSemanticTypeLowering(SGM.Types);
-  if (addrTL.isAddressOnly()) {
+  if (semanticTL.isAddressOnly()) {
     // Copy the address-only value.
     SILValue copy = getBufferForExprResult(loc, semanticTL.getLoweredType(), C);
     addrTL.emitSemanticLoadInto(B, loc, addr, copy, isTake, IsInitialization);

lib/SIL/SILInstruction.cpp

@@ -411,6 +411,11 @@ StoreInst::StoreInst(SILLocation Loc, SILValue Src, SILValue Dest)
     Operands(this, Src, Dest) {
 }
 
+StoreWeakInst::StoreWeakInst(SILLocation loc, SILValue value, SILValue dest,
+                             IsInitialization_t isInit)
+  : SILInstruction(ValueKind::StoreWeakInst, loc),
+    Operands(this, value, dest), IsInit(isInit) {
+}
 
 CopyAddrInst::CopyAddrInst(SILLocation Loc, SILValue SrcLValue, SILValue DestLValue,
                            IsTake_t isTakeOfSrc,

lib/SIL/SILPrinter.cpp

@@ -440,6 +440,15 @@ public:
     OS << "store " << getID(SI->getSrc()) << " to "
        << getIDAndType(SI->getDest());
   }
+  void visitLoadWeakInst(LoadWeakInst *LI) {
+    OS << "load_weak " << getIDAndType(LI->getOperand());
+  }
+  void visitStoreWeakInst(StoreWeakInst *SI) {
+    OS << "store_weak " << getID(SI->getSrc()) << " to ";
+    if (SI->isInitialization())
+      OS << "[initialization] ";
+    OS << getIDAndType(SI->getDest());
+  }
   void visitCopyAddrInst(CopyAddrInst *CI) {
     OS << "copy_addr ";
     if (CI->isTakeOfSrc())

lib/SIL/TypeLowering.cpp

@@ -470,6 +470,19 @@ bool SILType::isAddressOnly(CanType type, SILModule &M) {
   return classifyType(type, M) == LoweredTypeKind::AddressOnly;
 }
 
+/// Emit the semantic store operation on a reference type.
+static void emitReferenceSemanticStore(SILBuilder &B, SILLocation loc,
+                                       SILValue value, SILValue addr,
+                                       IsInitialization_t isInit) {
+  // FIXME: Use assign instruction here? Or maybe have two
+  // variants of this function, one for canonical, one for
+  // non-canonical.
+  SILValue old;
+  if (!isInit) old = B.createLoad(loc, addr);
+  B.createStore(loc, value, addr);
+  if (!isInit) B.createRelease(loc, old);
+}
+
 namespace {
   /// A class for loadable types.
   class LoadableTypeLowering : public TypeLowering {
@@ -684,13 +697,7 @@ namespace {
     void emitSemanticStore(SILBuilder &B, SILLocation loc,
                            SILValue value, SILValue addr,
                            IsInitialization_t isInit) const override {
-      // FIXME: Use assign instruction here? Or maybe have two
+      emitReferenceSemanticStore(B, loc, value, addr, isInit);
-      // variants of this function, one for canonical, one for
-      // non-canonical.
-      SILValue old;
-      if (!isInit) old = B.createLoad(loc, addr);
-      B.createStore(loc, value, addr);
-      if (!isInit) B.createRelease(loc, old);
     }
 
     SILValue emitSemanticLoad(SILBuilder &B, SILLocation loc,
@@ -788,20 +795,24 @@ namespace {
     void emitSemanticStore(SILBuilder &B, SILLocation loc,
                            SILValue value, SILValue addr,
                            IsInitialization_t isInit) const override {
-      // FIXME
+      B.createStoreWeak(loc, value, addr, isInit);
+
+      // store_weak does not consume a retain on its input, so we have
+      // to balance that out.
+      B.createRelease(loc, value);
     }
 
     SILValue emitSemanticLoad(SILBuilder &B, SILLocation loc,
                               SILValue addr, IsTake_t isTake) const override {
-      // FIXME
+      return B.createLoadWeak(loc, addr, isTake);
-      return SILValue();
     }
 
     void emitSemanticLoadInto(SILBuilder &B, SILLocation loc,
                               SILValue src, SILValue dest,
                               IsTake_t isTake,
                               IsInitialization_t isInit) const override {
-      // FIXME
+      auto value = B.createLoadWeak(loc, src, isTake);
+      emitReferenceSemanticStore(B, loc, value, dest, isInit);
     }
   };
 

stdlib/runtime/Alloc.cpp

@@ -441,8 +441,33 @@ extern "C" bool swift_isUniquelyReferenced(HeapObject *object) {
   return result;
 }
 
-void swift::swift_weakInit(WeakReference *ref) {
+void swift::swift_weakInit(WeakReference *ref, HeapObject *value) {
-  ref->Value = nullptr;
+  ref->Value = value;
+  swift_weakRetain(value);
+}
+
+void swift::swift_weakAssign(WeakReference *ref, HeapObject *newValue) {
+  swift_weakRetain(newValue);
+  auto oldValue = ref->Value;
+  ref->Value = newValue;
+  swift_weakRelease(oldValue);
+}
+
+HeapObject *swift::swift_weakLoadStrong(WeakReference *ref) {
+  auto object = ref->Value;
+  if (object == nullptr) return nullptr;
+  if (object->refCount & RC_DEALLOCATING_BIT) {
+    swift_weakRelease(object);
+    ref->Value = nullptr;
+    return nullptr;
+  }
+  return swift_tryRetain(object);
+}
+
+HeapObject *swift::swift_weakTakeStrong(WeakReference *ref) {
+  auto result = swift_weakLoadStrong(ref);
+  swift_weakDestroy(ref);
+  return result;
 }
 
 void swift::swift_weakDestroy(WeakReference *ref) {
@@ -488,17 +513,6 @@ void swift::swift_weakTakeAssign(WeakReference *dest, WeakReference *src) {
   swift_weakTakeInit(dest, src);
 }
 
-HeapObject *swift::swift_weakTryRetain(WeakReference *ref) {
-  auto object = ref->Value;
-  if (object == nullptr) return nullptr;
-  if (object->refCount & RC_DEALLOCATING_BIT) {
-    swift_weakRelease(object);
-    ref->Value = nullptr;
-    return nullptr;
-  }
-  return swift_tryRetain(object);
-}
-
 void swift::_swift_abortRetainUnowned(const void *object) {
   fprintf(stderr, "attempting to retain deallocated object at %p", object);
   abort();

test/SIL/SILGen/weak.swift

@@ -0,0 +1,37 @@
+// RUN: %swift -emit-silgen %s | FileCheck %s
+
+class C {}
+
+struct A {
+  var [weak] x : C
+}
+
+// CHECK:    sil @_T4weak5test0FT1cCS_1C_T_ : $[thin] (c : C) -> () {
+func test0(c : C) {
+// CHECK:    bb0(%0 : $C):
+// CHECK:      [[C:%.*]] = alloc_box $C
+
+  var a : A
+// CHECK:      [[A:%.*]] = alloc_box $A
+
+  var [weak] x = c
+// CHECK:      [[X:%.*]] = alloc_box $[weak] C
+// CHECK-NEXT: [[T0:%.*]] = load [[C]]#1 : $*C
+// CHECK-NEXT: retain [[T0]] : $C
+// CHECK-NEXT: store_weak [[T0]] to [initialization] [[X]]#1 : $*[weak] C
+// CHECK-NEXT: release [[T0]] : $C
+
+  a.x = c
+// CHECK-NEXT: [[T0:%.*]] = load [[C]]#1 : $*C
+// CHECK-NEXT: retain [[T0]] : $C
+// CHECK-NEXT: [[T1:%.*]] = struct_element_addr [[A]]#1 : $*A, #x
+// CHECK-NEXT: store_weak [[T0]] to [[T1]] : $*[weak] C
+// CHECK-NEXT: release [[T0]] : $C
+
+  a.x = x
+// CHECK-NEXT: [[T0:%.*]] = load_weak [[X]]#1 : $*[weak] C
+// CHECK-NEXT: [[T1:%.*]] = struct_element_addr [[A]]#1 : $*A, #x
+// CHECK-NEXT: store_weak [[T0]] to [[T1]] : $*[weak] C
+// CHECK-NEXT: release [[T0]] : $C
+
+}

unittests/runtime/Makefile

@@ -15,6 +15,8 @@ TESTNAME = runtime
 include $(SWIFT_LEVEL)/../../Makefile.config
 LINK_COMPONENTS := $(TARGETS_TO_BUILD)
 
+SOURCES = $(notdir $(wildcard $(PROJ_SRC_DIR)/*.cpp $(PROJ_SRC_DIR)/*.mm))
+
 # This is almost certainly not the right way of doing this.
 ProjLibsOptions += -lswift_stdlib_core
 

unittests/runtime/weak.mm

@@ -0,0 +1,287 @@
+//===- swift/unittests/runtime/weak.mm - Weak-pointer tests ---------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2015 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#include <Foundation/NSObject.h>
+#include "swift/Runtime/Alloc.h"
+#include "swift/Runtime/Metadata.h"
+#include "gtest/gtest.h"
+
+using namespace swift;
+
+// Declare some Objective-C stuff.
+extern "C" void objc_release(id);
+
+static unsigned DestroyedObjCCount = 0;
+
+/// A trivial class that increments DestroyedObjCCount when deallocated.
+@interface ObjCClass : NSObject @end
+@implementation ObjCClass
+- (void) dealloc {
+  DestroyedObjCCount++;
+  [super dealloc];
+}
+@end
+static HeapObject *make_objc_object() {
+  return (HeapObject*) [ObjCClass new];
+}
+
+// Make a Native Swift object by calling a constructor.
+extern "C" HeapObject *_TCSs6ObjectCfMS_FT_S_(void *unused);
+static HeapObject *make_swift_object() {
+  return _TCSs6ObjectCfMS_FT_S_(0);
+}
+
+static void unknown_release(void *value) {
+  objc_release((id) value);
+}
+
+TEST(WeakTest, preconditions) {
+  swift_release(make_swift_object());
+  unknown_release(make_objc_object());
+}
+
+TEST(WeakTest, simple_swift) {
+  HeapObject *o1 = make_swift_object();
+  HeapObject *o2 = make_swift_object();
+  ASSERT_NE(o1, o2);
+  ASSERT_NE(o1, nullptr);
+  ASSERT_NE(o2, nullptr);
+
+  WeakReference ref1;
+  swift_weakInit(&ref1, o1);
+
+  HeapObject *tmp = swift_weakLoadStrong(&ref1);
+  ASSERT_EQ(tmp, o1);
+  swift_release(tmp);
+
+  tmp = swift_weakLoadStrong(&ref1);
+  ASSERT_EQ(o1, tmp);
+  swift_release(tmp);
+
+  swift_weakAssign(&ref1, o2);
+  tmp = swift_weakLoadStrong(&ref1);
+  ASSERT_EQ(o2, tmp);
+  swift_release(tmp);
+
+  tmp = swift_weakLoadStrong(&ref1);
+  ASSERT_EQ(o2, tmp);
+  swift_release(tmp);
+
+  swift_release(o1);
+
+  tmp = swift_weakLoadStrong(&ref1);
+  ASSERT_EQ(o2, tmp);
+  swift_release(tmp);
+
+  swift_release(o2);
+
+  tmp = swift_weakLoadStrong(&ref1);
+  ASSERT_EQ(nullptr, tmp);
+  swift_release(tmp);
+
+  swift_weakDestroy(&ref1);
+}
+
+TEST(WeakTest, simple_objc) {
+  void *o1 = make_objc_object();
+  void *o2 = make_objc_object();
+  ASSERT_NE(o1, o2);
+  ASSERT_NE(o1, nullptr);
+  ASSERT_NE(o2, nullptr);
+
+  DestroyedObjCCount = 0;
+  
+  WeakReference ref1;
+  swift_unknownWeakInit(&ref1, o1);
+
+  void *tmp = swift_unknownWeakLoadStrong(&ref1);
+  ASSERT_EQ(tmp, o1);
+  unknown_release(tmp);
+
+  tmp = swift_unknownWeakLoadStrong(&ref1);
+  ASSERT_EQ(o1, tmp);
+  unknown_release(tmp);
+  ASSERT_EQ(0U, DestroyedObjCCount);
+
+  swift_unknownWeakAssign(&ref1, o2);
+  tmp = swift_unknownWeakLoadStrong(&ref1);
+  ASSERT_EQ(o2, tmp);
+  unknown_release(tmp);
+  ASSERT_EQ(0U, DestroyedObjCCount);
+
+  tmp = swift_unknownWeakLoadStrong(&ref1);
+  ASSERT_EQ(o2, tmp);
+  unknown_release(tmp);
+  ASSERT_EQ(0U, DestroyedObjCCount);
+
+  unknown_release(o1);
+  ASSERT_EQ(1U, DestroyedObjCCount);
+
+  tmp = swift_unknownWeakLoadStrong(&ref1);
+  ASSERT_EQ(o2, tmp);
+  unknown_release(tmp);
+  ASSERT_EQ(1U, DestroyedObjCCount);
+
+  unknown_release(o2);
+  ASSERT_EQ(2U, DestroyedObjCCount);
+
+  tmp = swift_unknownWeakLoadStrong(&ref1);
+  ASSERT_EQ(nullptr, tmp);
+  unknown_release(tmp);
+  ASSERT_EQ(2U, DestroyedObjCCount);
+
+  swift_unknownWeakDestroy(&ref1);
+}
+
+TEST(WeakTest, simple_swift_as_unknown) {
+  void *o1 = make_swift_object();
+  void *o2 = make_swift_object();
+  ASSERT_NE(o1, o2);
+  ASSERT_NE(o1, nullptr);
+  ASSERT_NE(o2, nullptr);
+
+  WeakReference ref1;
+  swift_unknownWeakInit(&ref1, o1);
+
+  void *tmp = swift_unknownWeakLoadStrong(&ref1);
+  ASSERT_EQ(tmp, o1);
+  unknown_release(tmp);
+
+  tmp = swift_unknownWeakLoadStrong(&ref1);
+  ASSERT_EQ(o1, tmp);
+  unknown_release(tmp);
+
+  swift_unknownWeakAssign(&ref1, o2);
+  tmp = swift_unknownWeakLoadStrong(&ref1);
+  ASSERT_EQ(o2, tmp);
+  unknown_release(tmp);
+
+  tmp = swift_unknownWeakLoadStrong(&ref1);
+  ASSERT_EQ(o2, tmp);
+  unknown_release(tmp);
+
+  unknown_release(o1);
+
+  tmp = swift_unknownWeakLoadStrong(&ref1);
+  ASSERT_EQ(o2, tmp);
+  unknown_release(tmp);
+
+  unknown_release(o2);
+
+  tmp = swift_unknownWeakLoadStrong(&ref1);
+  ASSERT_EQ(nullptr, tmp);
+  unknown_release(tmp);
+
+  swift_unknownWeakDestroy(&ref1);
+}
+
+TEST(WeakTest, simple_swift_and_objc) {
+  void *o1 = make_swift_object();
+  void *o2 = make_objc_object();
+  ASSERT_NE(o1, o2);
+  ASSERT_NE(o1, nullptr);
+  ASSERT_NE(o2, nullptr);
+
+  DestroyedObjCCount = 0;
+  
+  WeakReference ref1;
+  swift_unknownWeakInit(&ref1, o1);
+
+  void *tmp = swift_unknownWeakLoadStrong(&ref1);
+  ASSERT_EQ(tmp, o1);
+  unknown_release(tmp);
+
+  tmp = swift_unknownWeakLoadStrong(&ref1);
+  ASSERT_EQ(o1, tmp);
+  unknown_release(tmp);
+  ASSERT_EQ(0U, DestroyedObjCCount);
+
+  swift_unknownWeakAssign(&ref1, o2);
+  tmp = swift_unknownWeakLoadStrong(&ref1);
+  ASSERT_EQ(o2, tmp);
+  unknown_release(tmp);
+  ASSERT_EQ(0U, DestroyedObjCCount);
+
+  tmp = swift_unknownWeakLoadStrong(&ref1);
+  ASSERT_EQ(o2, tmp);
+  unknown_release(tmp);
+  ASSERT_EQ(0U, DestroyedObjCCount);
+
+  unknown_release(o1);
+  ASSERT_EQ(0U, DestroyedObjCCount);
+
+  tmp = swift_unknownWeakLoadStrong(&ref1);
+  ASSERT_EQ(o2, tmp);
+  unknown_release(tmp);
+  ASSERT_EQ(0U, DestroyedObjCCount);
+
+  unknown_release(o2);
+  ASSERT_EQ(1U, DestroyedObjCCount);
+
+  tmp = swift_unknownWeakLoadStrong(&ref1);
+  ASSERT_EQ(nullptr, tmp);
+  unknown_release(tmp);
+  ASSERT_EQ(1U, DestroyedObjCCount);
+
+  swift_unknownWeakDestroy(&ref1);
+}
+
+TEST(WeakTest, simple_objc_and_swift) {
+  void *o1 = make_objc_object();
+  void *o2 = make_swift_object();
+  ASSERT_NE(o1, o2);
+  ASSERT_NE(o1, nullptr);
+  ASSERT_NE(o2, nullptr);
+
+  DestroyedObjCCount = 0;
+  
+  WeakReference ref1;
+  swift_unknownWeakInit(&ref1, o1);
+
+  void *tmp = swift_unknownWeakLoadStrong(&ref1);
+  ASSERT_EQ(tmp, o1);
+  unknown_release(tmp);
+
+  tmp = swift_unknownWeakLoadStrong(&ref1);
+  ASSERT_EQ(o1, tmp);
+  unknown_release(tmp);
+  ASSERT_EQ(0U, DestroyedObjCCount);
+
+  swift_unknownWeakAssign(&ref1, o2);
+  tmp = swift_unknownWeakLoadStrong(&ref1);
+  ASSERT_EQ(o2, tmp);
+  unknown_release(tmp);
+  ASSERT_EQ(0U, DestroyedObjCCount);
+
+  tmp = swift_unknownWeakLoadStrong(&ref1);
+  ASSERT_EQ(o2, tmp);
+  unknown_release(tmp);
+  ASSERT_EQ(0U, DestroyedObjCCount);
+
+  unknown_release(o1);
+  ASSERT_EQ(1U, DestroyedObjCCount);
+
+  tmp = swift_unknownWeakLoadStrong(&ref1);
+  ASSERT_EQ(o2, tmp);
+  unknown_release(tmp);
+  ASSERT_EQ(1U, DestroyedObjCCount);
+
+  unknown_release(o2);
+  ASSERT_EQ(1U, DestroyedObjCCount);
+
+  tmp = swift_unknownWeakLoadStrong(&ref1);
+  ASSERT_EQ(nullptr, tmp);
+  unknown_release(tmp);
+  ASSERT_EQ(1U, DestroyedObjCCount);
+
+  swift_unknownWeakDestroy(&ref1);
+}