2011/1/27 Stefan Behnel <[email protected]>:
> Vitja Makarov, 27.01.2011 10:02:
>> 2011/1/27 Stefan Behnel:
>>> Vitja Makarov, 27.01.2011 08:25:
>>>>>> 2011/1/25 Stefan Behnel:
>>>>>>> Vitja Makarov, 25.01.2011 10:01:
>>>>>>>> 2011/1/25 Stefan Behnel:
>>>>>>>>> def x():
>>>>>>>>> do_some_stuff()
>>>>>>>>>
>>>>>>>>> return # disable rest of code, e.g. during debugging
>>>>>>>>>
>>>>>>>>> unreachable_code()
>>>>>>>>>
>>>>>>>>> Cython shouldn't bother generating dead code here (even if the C
>>>>>>>>> compiler
>>>>>>>>> would drop it anyway).
>>>>>>>>
>>>>>>>> That should be rather easy to do: remove all the nodes in StatList
>>>>>>>> after: break, continue, return, raise, something else?
>>>>>>>
>>>>>>> Careful, this may involve recursive propagation through helper nodes.
>>>>>>> The
>>>>>>> tree isn't always as simple as that.
>>>>>>>
>>>>>>> I think an attribute "is_terminator" on Nodes might do the job. It's
>>>>>>> set to
>>>>>>> False by default and to True on all nodes you mentioned above, and is
>>>>>>> inherited by StatListNode if its last node is a terminator (while
>>>>>>> dropping
>>>>>>> its remaining child nodes at the same time) and by all helper nodes that
>>>>>>> contain StatListNodes. This could be done in analyse_types() (or maybe
>>>>>>> earlier?).
>>>>
>>>> Ok. I've moved it into ParseTreeTransforms and created branch:
>>>>
>>>> https://github.com/vitek/cython/commit/a8e957ec29f0448ee7c43bd3969012772d09b236
>>>
>>> the StatListNode (and
>>> other nodes) should inherit the flag from their last child.
>>
>> This could be done simply in RemoveUnreachableCode
>>
>> node.is_terminator = True
>
> Sure.
>
>
>> I don't actually understand where could be that used later?
>
> Well, if you recursively propagate the flag through nodes that support it,
> you may end up in another StatListNode that strip its trailing dead code.
> Look through UtilNodes.py, there are a couple of nodes that can wrap
> Stat(List)Nodes. Maybe check Nodes.py also, not sure if there aren't any
> other nodes that can safely assume that a terminator at the end of their
> last child makes them a terminator as well.
>
>
return and loop-controls are very different here
if cond:
return 1
else:
return 0
# dead code follows
We can set is_terminator here if all the clauses are terminators
for i in a:
if i > 0:
continue
else
break
# dead code here
for i in a:
return
# not dead
for i in a:
return
else:
return
# dead
It seems to me that each case should be handled its own way.
We can't simply say: this node have child with is_terminator set so
it's terminator too.
Is there a way to write tests for warnings? If no think we should create one.
>>>> Some error tests do fail because nodes are removed and code generation
>>>> time error is omited.
>>>
>>> That should be fixable in most cases. We could also use a compiler option
>>> that disables dead code removal, and then use it in the error tests.
>>
>> Hmm, not sure here.
>> I think it should be better to move checks outside code generation.
>
> Ah, ok, I misunderstood you then. Yes, errors should no longer occur at
> code generation time.
>
Think that's whole lot of work.
When implementing generators I've moved error checking into ParseTreeTransforms
and left 'yield not supported' in YieldExprNode. That could be later
replaced with: raise InternalError
--
vitja.
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