Fix for https://youtrack.jetbrains.com/issue/KT-35940 + test

The bug was not taking into account implicit runtime DFG edges generated
by associated objects in devirtualization analysis

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/optimizations/Devirtualization.kt

@@ -13,6 +13,7 @@ import org.jetbrains.kotlin.backend.common.push
 import org.jetbrains.kotlin.backend.common.lower.createIrBuilder
 import org.jetbrains.kotlin.backend.common.lower.irBlock
 import org.jetbrains.kotlin.backend.konan.*
+import org.jetbrains.kotlin.descriptors.ClassKind
 import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.builders.*
 import org.jetbrains.kotlin.ir.declarations.*
@@ -257,6 +258,22 @@ internal object Devirtualization {
                 } else {
                     // String is implicitly created as argument of <main>.
                     addInstantiatingClass(symbolTable.mapType(context.irBuiltIns.stringType))
+
+                    // Conservatively assume each associated object could be instantiated.
+                    context.irModule!!.acceptChildrenVoid(object: IrElementVisitorVoid {
+                        override fun visitElement(element: IrElement) {
+                            element.acceptChildrenVoid(this)
+                        }
+
+                        override fun visitClass(declaration: IrClass) {
+                            context.getLayoutBuilder(declaration).associatedObjects.values.forEach {
+                                assert (it.kind == ClassKind.OBJECT) { "An object expected but was ${it.dump()}" }
+                                addInstantiatingClass(symbolTable.mapType(it.defaultType))
+                            }
+                            super.visitClass(declaration)
+                        }
+                    })
+
                 }
                 // Traverse call graph from the roots.
                 rootSet.forEach { dfs(it, it.returnParameter.type) }

backend.native/tests/codegen/associatedObjects/associatedObjects1.kt

@@ -45,14 +45,23 @@ object Baz
 fun testGlobalOptimizations1() {
     val i1 = I1ImplHolder::class.findAssociatedObject<Associated1>()!! as I1
     assertEquals(42, i1.foo())
+    val c = C(null)
+    i1.bar(c)
+    assertEquals("zzz", c.list!![0])
 }
 
+private class C(var list: List<String>?)
+
 private interface I1 {
     fun foo(): Int
+    fun bar(c: C)
 }
 
 private object I1Impl : I1 {
     override fun foo() = 42
+    override fun bar(c: C) {
+        c.list = mutableListOf("zzz")
+    }
 }
 
 @Associated1(I1Impl::class)