Add regression tests for obsolete issues

#KT-50909
 #KT-50974
 #KT-51888

compiler/testData/codegen/box/inlineClasses/kt50909.kt

@@ -0,0 +1,17 @@
+// TARGET_BACKEND: JVM_IR
+// WITH_STDLIB
+
+data class Parent(val child: Parent.Child?) {
+    val result =
+        if (this.child == null) foo(this.child)
+        else "Fail"
+
+    @JvmInline
+    value class Child(val value: String)
+}
+
+fun foo(x: String?): String =
+    x ?: "OK"
+
+fun box(): String =
+    Parent(null).result

compiler/testData/codegen/box/inlineClasses/kt50974_resultMultiModule.kt

@@ -0,0 +1,29 @@
+// IGNORE_LIGHT_ANALYSIS
+// IGNORE_BACKEND: JVM
+// WITH_STDLIB
+// MODULE: lib
+// FILE: lib.kt
+
+public class WhateverUseCase : UseCaseWithParameter<Result<Int>, Int> {
+    override operator fun invoke(param: Result<Int>): Result<Int> {
+        return param.onFailure {
+            return if (it is NumberFormatException)
+                Result.success(0)
+            else
+                Result.failure(it)
+        }
+    }
+}
+
+interface UseCaseWithParameter<P, R> {
+    operator fun invoke(param: P) : Result<R>
+}
+
+// MODULE: main(lib)
+// FILE: main.kt
+
+fun box(): String {
+    val useCase = WhateverUseCase()
+    return if (useCase(Result.failure(NumberFormatException())) == Result.success(0)) "OK"
+        else "Fail"
+}

compiler/testData/codegen/box/jvm8/defaults/nonDefaultInheritance/diamondWithJava.kt

@@ -0,0 +1,26 @@
+// TARGET_BACKEND: JVM_IR
+// JVM_TARGET: 1.8
+// MODULE: lib
+// !JVM_DEFAULT_MODE: all
+// FILE: P.java
+
+public interface P {
+    default String test() {
+        return "OK";
+    }
+}
+
+// FILE: kotlin.kt
+
+abstract class A : P
+
+interface B : P
+
+// MODULE: main(lib)
+// !JVM_DEFAULT_MODE: disable
+// FILE: main.kt
+abstract class C : A(), P, B
+
+fun box(): String {
+    return object : C() {}.test()
+}