Fix a bug where a constructor call of an open class is devirtualized …

…although the call should be done dynamically.

fixes rdar://problem/28882879

lib/SILOptimizer/Utils/Local.cpp

@@ -2719,8 +2719,12 @@ bool swift::calleesAreStaticallyKnowable(SILModule &M, SILDeclRef Decl) {
   case Accessibility::Open:
     return false;
   case Accessibility::Public:
-    if (auto ctor = dyn_cast<ConstructorDecl>(AFD)) {
-      if (ctor->isRequired())
+    if (isa<ConstructorDecl>(AFD)) {
+      // Constructors are special: a derived class in another module can
+      // "override" a constructor if its class is "open", although the
+      // constructor itself is not open.
+      auto *ND = AFD->getExtensionType()->getNominalOrBoundGenericNominal();
+      if (ND->getEffectiveAccess() == Accessibility::Open)
         return false;
     }
     SWIFT_FALLTHROUGH;

test/SILOptimizer/mandatory_inlining_devirt.swift

@@ -0,0 +1,32 @@
+// RUN: %target-swift-frontend %s -module-name test -emit-sil -o - -verify | %FileCheck %s
+
+
+// Constructor calls are dispatched dynamically for open classes, even if
+// the constructor itself is not "open".
+
+open class OpenClass {
+  // CHECK-LABEL: sil @_TFC4test9OpenClasscfT1xSi_S0_ : $@convention(method) (Int, @owned OpenClass) -> @owned OpenClass
+  // CHECK: [[M:%[0-9]+]] = class_method %1 : $OpenClass, #OpenClass.init!initializer.1 : (OpenClass.Type) -> (Int, Int) -> OpenClass
+  // CHECK: apply [[M]]
+  // CHECK: return
+  public convenience init(x: Int) {
+    self.init(x: x, y: 27)
+  }
+  public init(x: Int, y: Int) {
+  }
+}
+
+// Static dispatch for not-open class (we are compiling with -wmo).
+
+public class PublicClass {
+  // CHECK-LABEL: sil @_TFC4test11PublicClasscfT1xSi_S0_ : $@convention(method) (Int, @owned PublicClass) -> @owned PublicClass
+  // CHECK: [[M:%[0-9]+]] = function_ref @_TFC4test11PublicClasscfT1xSi1ySi_S0_ : $@convention(method) (Int, Int, @owned PublicClass) -> @owned PublicClass
+  // CHECK: apply [[M]]
+  // CHECK: return
+  public convenience init(x: Int) {
+    self.init(x: x, y: 27)
+  }
+  public init(x: Int, y: Int) {
+  }
+}
+