[DI] InitAccessors: Use of SILModule::getFieldIndex is incompatible with DI data structures

DI cares only about stored fields of the current type but `SILModule::getFieldIndex`
goes through all of the supertypes as well.

Author: xedin

lib/SILOptimizer/Mandatory/DIMemoryUseCollector.cpp

@@ -1200,13 +1200,23 @@ ElementUseCollector::collectAssignOrInitUses(AssignOrInitInst *Inst,
                      ->getDeclContext()
                      ->getSelfNominalTypeDecl();
 
+  auto expansionContext = TypeExpansionContext(TheMemory.getFunction());
+
   auto selfTy = Inst->getSelf()->getType();
 
   auto addUse = [&](VarDecl *property, DIUseKind useKind) {
-    auto expansionContext = TypeExpansionContext(*Inst->getFunction());
+    unsigned fieldIdx = 0;
+    for (auto *VD : typeDC->getStoredProperties()) {
+      if (VD == property)
+        break;
+
+      fieldIdx += getElementCountRec(
+          expansionContext, Module,
+          selfTy.getFieldType(VD, Module, expansionContext), false);
+    }
+
     auto type = selfTy.getFieldType(property, Module, expansionContext);
-    addElementUses(Module.getFieldIndex(typeDC, property), type, Inst, useKind,
-                   property);
+    addElementUses(fieldIdx, type, Inst, useKind, property);
   };
 
   auto initializedElts = Inst->getInitializedProperties();

test/Interpreter/init_accessors.swift

@@ -709,3 +709,44 @@ test_properties_with_inits()
 // CHECK-NEXT: TestAssign in x.init: self.x = S(x: 0)
 // CHECK-NEXT: TestAssign: self.x = S(x: -3)
 // CHECK-NEXT: test-init-expr-3: TestDefault(a: 42, b: <<default>>)
+
+func test_inheritance() {
+  class Entity {
+    var _age: Int = 0
+    var age: Int = 0 {
+      @storageRestrictions(initializes: _age)
+      init { _age = newValue }
+      get { _age }
+      set { _age = newValue }
+    }
+  }
+
+  class Person : Entity, CustomStringConvertible {
+    var _firstName: String
+    var firstName: String = "<<unknown>>" {
+      @storageRestrictions(initializes: _firstName)
+      init { _firstName = newValue }
+      get { _firstName }
+      set { _firstName = newValue }
+    }
+
+    var description: String {
+      "Person(firstName: \(firstName), age: \(age))"
+    }
+
+    override init() {}
+
+    init(firstName: String, age: Int) {
+      super.init()
+      self.firstName = firstName
+      self.age = age
+    }
+  }
+
+  print("test-inheritance-1: \(Person())")
+  print("test-inheritance-2: \(Person(firstName: "Q", age: 42))")
+}
+
+test_inheritance()
+// CHECK: test-inheritance-1: Person(firstName: <<unknown>>, age: 0)
+// CHECK-NEXT: test-inheritance-2: Person(firstName: Q, age: 42)