Coerce any type to Number before unboxing

compiler/backend/src/org/jetbrains/jet/codegen/StackValue.java

@@ -294,16 +294,14 @@ public abstract class StackValue {
             }
         }
         else if (fromType.getSort() == Type.OBJECT && toType.getSort() <= Type.DOUBLE) {
-            if (fromType.equals(OBJECT_TYPE)) {
-                if (toType.getSort() == Type.BOOLEAN) {
-                    v.checkcast(JvmPrimitiveType.BOOLEAN.getWrapper().getAsmType());
-                }
-                else if (toType.getSort() == Type.CHAR) {
-                    v.checkcast(JvmPrimitiveType.CHAR.getWrapper().getAsmType());
-                }
-                else {
-                    v.checkcast(getType(Number.class));
-                }
+            if (toType.getSort() == Type.BOOLEAN) {
+                coerce(fromType, JvmPrimitiveType.BOOLEAN.getWrapper().getAsmType(), v);
+            }
+            else if (toType.getSort() == Type.CHAR) {
+                coerce(fromType, JvmPrimitiveType.CHAR.getWrapper().getAsmType(), v);
+            }
+            else {
+                coerce(fromType, getType(Number.class), v);
             }
             unbox(toType, v);
         }

compiler/testData/codegen/primitiveTypes/unboxComparable.kt

@@ -0,0 +1,5 @@
+fun foo(x: Int) = x
+
+fun bar(x: Comparable<Int>) = if (x is Int) foo(x) else 0
+
+fun box() = if (bar(42) == 42) "OK" else "Fail"

compiler/tests/org/jetbrains/jet/codegen/PrimitiveTypesTest.java

@@ -456,4 +456,8 @@ public class PrimitiveTypesTest extends CodegenTestCase {
     public void test2794() throws Exception {
         blackBoxFile("regressions/kt2794.kt");
     }
+
+    public void testUnboxComparable() {
+        blackBoxFile("primitiveTypes/unboxComparable.kt");
+    }
 }