Invalidate callsite

[Isaiah Peng]

Hi guys,

My name is Isaiah, I'm currently trying to implement invokedynamic for my
Python 3 implementation. Everything went quite well until I encountered a
`ClassCastException` which I don't know how to fix.

Here is my theory: there are two method calls that has the same arity, with
signatures of:

`(LPyObject;LThreadState;[LPyObject;LString;)LPyObject`
and
`(LPyObject;LThreadState;LPyObject;LPyObject)LPyObject`

The former is for methods that take vararg and keyword arguments, the later
is for methods that take two arguments. The stacktrace is as following:

java.lang.ClassCastException: Cannot cast [Ljava.lang.String; to
org.python.core.PyObject

        at java.base/java.lang.Class.cast(Class.java:3578)
        at contextlib_jython_36.__init__$12(contextlib:67)
        at org.python.core.Py.runCode(Py.java:1663)
        at org.python.core.PyTableCode.call(PyTableCode.java:404)
        at org.python.core.PyTableCode.call(PyTableCode.java:382)
        at org.python.core.PyFunction.__call__(PyFunction.java:442)
        at
org.python.core.PyMethod.instancemethod___call__(PyMethod.java:237)
        at org.python.core.PyMethod.__call__(PyMethod.java:228)
        at org.python.core.PyMethod.__call__(PyMethod.java:223)
        at org.python.core.Deriveds.dispatch__init__(Deriveds.java:19)
        at
org.python.core.PyObjectDerived.dispatch__init__(PyObjectDerived.java:940)
        at org.python.core.PyType.type___call__(PyType.java:1675)
        at org.python.core.PyType$type___call___exposer.__call__(Unknown
Source)
        at org.python.core.PyTypeDerived.__call__(PyTypeDerived.java:831)
        at org.python.core.PyObject.__call__(PyObject.java:506)
        at org.python.core.PyObject.__call__(PyObject.java:510)
        at contextlib_jython_36.helper$17(contextlib:159)

The GuardedInvocation returned from the linker is like:

`return new GuardedInvocation(mh, null, new SwitchPoint[0],
ClassCastException.class);`

It seems to be able to catch the class cast exception for the receiver but
not for arguments. I create a similar call path and the function works
fine, so I thought the cause could be the callsite is not invalidated.

My question is: Is my guess correct? if so why does it reuse the callsite
when the signatures are different? and how to create a guard for such case?

The source code can be found here:

https://bitbucket.org/jylang/jylang/src/e0c64d17b21db7784c75892424cae09f9faa07d3/src/org/python/core/PyFunction.java?at=indy&fileviewer=file-view-default#PyFunction.java-513

Thanks in advance,
Isaiah Peng