[5.9][IRGen] Respect optionality of unowned(unsafe) reference properties

lib/IRGen/GenExistential.cpp

@@ -798,6 +798,7 @@ namespace {
   class Name##ClassExistentialTypeInfo final \
     : public ScalarExistentialTypeInfoBase<Name##ClassExistentialTypeInfo, \
                                            LoadableTypeInfo> { \
+  bool IsOptional; \
   public: \
     Name##ClassExistentialTypeInfo( \
         ArrayRef<const ProtocolDecl *> storedProtocols, \
@@ -807,7 +808,8 @@ namespace {
         bool isOptional) \
       : ScalarExistentialTypeInfoBase(storedProtocols, ty, size, \
                                       spareBits, align, IsTriviallyDestroyable,\
-                                      IsCopyable, IsFixedSize) {} \
+                                      IsCopyable, IsFixedSize), \
+        IsOptional(isOptional) {} \
     TypeLayoutEntry \
     *buildTypeLayoutEntry(IRGenModule &IGM, \
                           SILType T, \
@@ -824,6 +826,25 @@ namespace {
       else \
         return IGM.getUnknownObjectTypeInfo(); \
     } \
+    unsigned getFixedExtraInhabitantCount(IRGenModule &IGM) const override { \
+      return getValueTypeInfoForExtraInhabitants(IGM) \
+                  .getFixedExtraInhabitantCount(IGM) - IsOptional; \
+    } \
+    APInt getFixedExtraInhabitantValue(IRGenModule &IGM, \
+                                       unsigned bits, \
+                                       unsigned index) const override { \
+      /* Note that we pass down the original bit-width. */ \
+      return getValueTypeInfoForExtraInhabitants(IGM) \
+                  .getFixedExtraInhabitantValue(IGM, bits, \
+                                                index + IsOptional); \
+    } \
+    llvm::Value *getExtraInhabitantIndex(IRGenFunction &IGF, \
+                                         Address src, SILType T, \
+                                         bool isOutlined) const override { \
+      return PointerInfo::forHeapObject(IGF.IGM) \
+        .withNullable(IsNullable_t(IsOptional)) \
+        .getExtraInhabitantIndex(IGF, src); \
+    } \
     /* FIXME -- Use REF_STORAGE_HELPER and make */ \
     /* getValueTypeInfoForExtraInhabitants call llvm_unreachable() */ \
     void emitValueRetain(IRGenFunction &IGF, llvm::Value *value, \

test/Interpreter/rdar108705703.swift

@@ -0,0 +1,28 @@
+// RUN: %target-run-simple-swift | %FileCheck %s
+// REQUIRES: executable_test
+
+struct Context {
+    unowned(unsafe) var x: AnyObject? = nil
+}
+
+@inline(never)
+func test(x: Context) -> Context? {
+  return x
+}
+
+// CHECK: works
+if (test(x: Context()) == nil) {
+    print("bug")
+} else {
+    print("works")
+}
+
+@inline(never)
+func test2() -> Context {
+  var g: [Context]  = [Context()]
+  print(g.endIndex)
+  return g.removeLast()
+}
+
+// CHECK: Context(x: nil)
+print(test2())