[9] RFR(M): 8040213: C2 does not put all modified nodes on IGVN worklist

[Vladimir Kozlov]

C->modified_nodes() is called only from debug code so you can simplify 
it by putting whole method inside DEBUG_ONLY() instead of different return:

DEBUG_ONLY( Unique_Node_List* modified_nodes() const { return 
_modified_nodes; } )

Otherwise look good.

Thanks,
Vladimir

On 7/22/14 1:15 AM, Tobias Hartmann wrote:
> Hi Vladimir,
>
> On 21.07.2014 19:13, Vladimir Kozlov wrote:
>> > Thanks for the hint, the optimized build did not work. I'm now using
>> > PRODUCT_RETURN and NOT_PRODUCT to guard the verification code. This is
>> > consistent with other verification methods like
>> > Compile::verify_graph_edges(..).
>>
>> The logic which verifies modified nodes in phaseX.cpp is under #ifdef
>> ASSERT. Yes, you are not collecting data in optimized VM by returning
>> NULL from modified_nodes(). But it is very confusing. I would suggest
>> to move all this code to debug build only. You can use
>> NOT_DEBUG_RETURN instead of PRODUCT_RETURN and put definitions under
>> #ifdef ASSERT in compile.cpp file.
>
> Okay, that's true. I missed that there is a NOT_DEBUG_RETURN. Now using it.
>
> New webrev: http://cr.openjdk.java.net/~thartmann/8040213/webrev.04/
>
> Thanks,
> Tobias
>
>>
>> Thanks,
>> Vladimir
>>
>> On 7/21/14 2:50 AM, Tobias Hartmann wrote:
>>> Vladimir, John, thanks for the review.
>>>
>>> On 18.07.2014 01:32, John Rose wrote:
>>>> On Jul 17, 2014, at 3:32 PM, Vladimir Kozlov
>>>> <vladimir.kozlov at oracle.com> wrote:
>>>>
>>>>> Initial prototype was written by me so part of changes are mine.
>>>>>
>>>>> On 7/17/14 3:40 AM, Tobias Hartmann wrote:
>>>>>> Hi John,
>>>>>>
>>>>>> thanks a lot for the detailed review! Please see comments inline.
>>>>>>
>>>>>> On 16.07.2014 01:10, John Rose wrote:
>>>>>>>>> Done. New webrev:
>>>>>>>>> http://cr.openjdk.java.net/~thartmann/8040213/webrev.01/
>>>>>>> Loading C->_modified_nodes with a stack address is bad news, even if
>>>>>>> the code apparently cleans it up on exit.  (I say "apparently"
>>>>>>> because
>>>>>>> there are early exits from that block, and the cleanup is not RAII
>>>>>>> style.)  I strongly suggest heap allocation instead of stack
>>>>>>> allocation; it's expensive but it's for debug code.
>>>>> The list array allocation is done in compiler arena which is cleaned
>>>>> after compilation finished by ResourceMark, only descriptor is on
>>>>> stack:
>>>>>
>>>>> +   Unique_Node_List modified_nodes(comp_arena());
>>>>>
>>>>> It is our normal style. We do it a lot, see Compile::Code_Gen().
>>>> Yes, we do it when adding phase control blocks to the Compile object,
>>>> within the tree of calls rooted at the constructor.  I see that the
>>>> new code is arguably part of that pattern.  I hope that is an
>>>> exceptional use of this style?
>>>>
>>>> Note that C2Compiler::compile_method creates the Compile object and
>>>> then queries it.  When it queries it, the Compile object may contain
>>>> dangling pointers into phase control blocks stored on the stack
>>>> (during subroutine calls like Code_Gen) but now deallocated.
>>>>
>>>> It seems to me that we avoid touching those dangling pointers by
>>>> simple will power and discipline.   Such a style doesn't scale, since
>>>> it's too easy to make mistakes as the code gets complicated.
>>>>
>>>>> Tobias, if you want to allocate Unique_Node_List object on arena:
>>>>>
>>>>> _modified_nodes = new (comp_arena()) Unique_Node_List(comp_arena());
>>>> That makes me feel much better.
>>>>
>>>> I would prefer for us to do it this way for the other stack-chunks
>>>> also, but that would be outside the scope of this bug.
>>>
>>> I changed it to heap allocation.
>>>
>>>> Tobias, thanks for doing this work.
>>>>
>>>> — John
>>>>
>>>>>> There are other places in the code where this is done, for example in
>>>>>> Compile::Compile(..) the Unique_Node_List 'for_igvn' is created on
>>>>>> the
>>>>>> stack. Is this a special case?
>>>>>>
>>>>>> I'm not sure how to correctly allocate the object on the heap. Do I
>>>>>> have
>>>>>> to use new/delete or is this handled by some magic in
>>>>>> "ResourceObject'?
>>>>>>
>>>>>>
>>>>>>> You inserted '#ifdef ASSERT' after
>>>>>>> 'PhaseIterGVN::verify_PhaseIterGVN', but I don't think you need it,
>>>>>>> since all of the code (including the similar insertion a few
>>>>>>> lines up)
>>>>>>> is '#ifndef PRODUCT'.  See also suggestion above regarding
>>>>>>> 'modified_nodes'.
>>>>> #ifndef PRODUCT is also 'optimized' version of VM. n->dump() method
>>>>> is not defined in optimized build. That is why asserts are needed.
>>>>>
>>>>> Tobias, please, build 'optimized' VM to verify your changes.
>>>
>>> Thanks for the hint, the optimized build did not work. I'm now using
>>> PRODUCT_RETURN and NOT_PRODUCT to guard the verification code. This is
>>> consistent with other verification methods like
>>> Compile::verify_graph_edges(..).
>>>
>>> New webrev: http://cr.openjdk.java.net/~thartmann/8040213/webrev.03/
>>>
>>> Thanks,
>>> Tobias
>>>
>>>>> Thanks,
>>>>> Vladimir
>>>>>
>>>>>> True, I removed the #ifdef.
>>>>>>
>>>>>>> There are a few places where tests like 'while
>>>>>>> (modified_list->size())' appears but there is no null check of
>>>>>>> 'modified_list' itself.  This could cause a crash if we ever get the
>>>>>>> phasing wrong; consider an assert or explicit null check 'while
>>>>>>> (modified_list != NULL && ...)'.
>>>>>> I added explicit null checks.
>>>>>>
>>>>>>
>>>>>> New webrev: http://cr.openjdk.java.net/~thartmann/8040213/webrev.02/
>>>>>>
>>>>>> Thanks,
>>>>>> Tobias
>>>>>>
>>>>>>> — John
>