[SILGen] InitAccessors: Don't use init accessor to initialize superclass properties

`super.init()` should fully initialize "super" which means that
such properties are mutated via a setter.

(cherry picked from commit c87daab)

Author: xedin

lib/SILGen/SILGenLValue.cpp

@@ -1642,6 +1642,14 @@ namespace {
       if (!isAssignmentToSelfParamInInit)
         return false;
 
+      // Properties declared in a superclass cannot be initialized via
+      // init accessor because `super.init()` should always precede
+      // any such property reference which means that it can only be
+      // mutated by a setter call.
+      if (varDecl->getDeclContext()->getSelfNominalTypeDecl() !=
+          fnDecl->getDeclContext()->getSelfNominalTypeDecl())
+        return false;
+
       auto *initAccessor = varDecl->getAccessor(AccessorKind::Init);
       if (!initAccessor)
         return false;

test/SILOptimizer/init_accessor_definite_init_diagnostics.swift

@@ -247,3 +247,26 @@ do {
     }
   }
 }
+
+do {
+  class Entity {
+    var _age: Int
+    var age: Int = 0 {
+      @storageRestrictions(initializes: _age)
+      init { _age = newValue }
+      get { _age }
+      set { _age = newValue }
+    }
+  }
+
+  class Person : Entity {
+    init(age: Int) {
+      self.age = age // expected-error {{'self' used in property access 'age' before 'super.init' call}}
+    }
+
+    init(otherAge: Int) {
+      super.init()
+      self.age = otherAge // Ok
+    }
+  }
+}

test/SILOptimizer/init_accessor_raw_sil_lowering.swift

@@ -2,6 +2,7 @@
 
 // REQUIRES: asserts
 
+
 struct Test1 {
   var _a: Int
   var _b: String
@@ -264,3 +265,27 @@ func test_default_inits() {
     // CHECK: assign_or_init [init] self %0 : $Test4, value [[Y_VALUE]] : $String, init {{.*}} : $@convention(thin) (@owned String) -> @out String, set undef : $@convention(thin) (@owned String) -> @out String
   }
 }
+
+func test_handling_of_superclass_properties() {
+  class Entity {
+    var _age: Int
+    var age: Int = 0 {
+      @storageRestrictions(initializes: _age)
+      init { _age = newValue }
+      get { _age }
+      set { _age = newValue }
+    }
+  }
+
+  class Person : Entity {
+    // CHECK-LABEL: sil private [ossa] @$s23assign_or_init_lowering38test_handling_of_superclass_propertiesyyF6PersonL_C3ageADSi_tcfc : $@convention(method) (Int, @owned Person) -> @owned Person
+    // CHECK: [[SELF:%.*]] = load [copy] %2 : $*Person
+    // CHECK-NEXT: [[SELF_AS_ENTITY:%.*]] = upcast [[SELF]] : $Person to $Entity
+    // CHECK-NEXT: [[AGE_SETTER:%.*]] = class_method [[SELF_AS_ENTITY]] : $Entity, #<abstract function>Entity.age!setter : (Entity) -> (Int) -> (), $@convention(method) (Int, @guaranteed Entity) -> ()
+    // CHECK-NEXT: {{.*}} = apply [[AGE_SETTER]](%0, [[SELF_AS_ENTITY]]) : $@convention(method) (Int, @guaranteed Entity) -> ()
+    init(age: Int) {
+      super.init()
+      self.age = age
+    }
+  }
+}