Pop return value after implicit coercion to unit

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/interpreter/IrInterpreter.kt

@@ -480,7 +480,10 @@ class IrInterpreter(irModule: IrModuleFragment) {
 
     private fun interpretTypeOperatorCall(expression: IrTypeOperatorCall, data: Frame): Code {
         return when (expression.operator) {
-            IrTypeOperator.IMPLICIT_COERCION_TO_UNIT -> expression.argument.interpret(data)
+            IrTypeOperator.IMPLICIT_COERCION_TO_UNIT -> {
+                // coercion to unit means that return value isn't used
+                expression.argument.interpret(data).apply { if (this == Code.NEXT) data.popReturnValue() }
+            }
             IrTypeOperator.CAST, IrTypeOperator.IMPLICIT_CAST -> {
                 val code = expression.argument.interpret(data)
                 if (!data.peekReturnValue().irClass.defaultType.isSubtypeOf(expression.type, irBuiltIns)) {

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/interpreter/stack/State.kt

@@ -35,7 +35,16 @@ interface State {
     }
 
     fun setState(newVar: Variable)
+
+    /**
+     * This method is used for passing a copy of a state.
+     * It is necessary then copy change its state's value, but the original one must remain the same.
+     *
+     * @see copyReceivedValue.kt
+     * @see tryFinally.kt
+     */
     fun copy(): State
+
     fun getIrFunction(descriptor: FunctionDescriptor): IrFunction?
 }