[pypy-dev] small problem with return values

Christian Tismer tismer at stackless.com
Thu Mar 16 03:00:59 CET 2006

Hi friends,

today I stumbled over a tiny problem.
I'm actually not sure how to fix it, so here it is:

When we annotate a function in a way that it does not return
a value, but we happen to use its return value, this case
is not caught early, but very late in backend_optimizations.

An example is here:

See line 77, where we call something that has no return value:

def call_destructor(thing):
     ll_call_destructor(thing)  # <<========== if you use return here
     # then we crash in backend_optimizations

The ll_call_destructor call is actually mapped this way:


and the rtype function is this:

def rtype_destruct_object(hop):
     v_any, = hop.inputargs(hop.args_r[0])
     return hop.genop('gc_unprotect', [v_any], resulttype=lltype.Void)

As you can see, the rtype func returns lltype.Void, nothing.

I think the backend_optimization does a cleanup and removes
the unused return variable from the ll function's graph,
but then it is required because we return this value.

Question: should we silently ignore this case, or raise an exception?
It would need a more exact check that we don't pass variables around
which are really Void.

ciao - chris

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