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From Naveen Neelakantam <neela...@illinois.edu>
Subject Re: Fwd: [jira] Created: (HARMONY-6007) [drlvm][jit][abcd] classic abcd pass fixes
Date Fri, 05 Dec 2008 17:28:13 GMT
(snip)

On 12/2/2008 6:34 AM, Egor Pasko wrote:
>>>>>> In my opinion something must be done here, or ABCD should simply
be
>>>>>> disabled as it is otherwise crippled.
>>>>>>
>>>>>>              
>>>>> currently ABCD should be correct, but not that capable. We should
>>>>> re-enable the capabilities. I am not seeing the reason to disable it
>>>>> now.
>>>>>
>>>>> Let's go this way. You try to make extra edges in InequalityGraph as
I
>>>>> described, if this does not work, I'll go hunting my memories and fix
>>>>> it. That may imply taking your original approach. :)
>>>>>
>>>>>            
>>>> I'm convinced simply adding extra edges won't work.  I can try to use
>>>> the BidirectionalBubbleSort example to demonstrate why, but expect a
>>>> delay.  :-)
>>>>
>>>>          
>>> hm, it worked earlier. The HIR changed locally, so should work
>>> now. Your demonstration would be a really hard work.. ;
>>>        
>> I'm confused why you think it would be hard.  ABCD currently does not
>> eliminate the bounds checks from BidirectionalBubbleSort...
>>      
>
> on first implementation we checked BidirectionalBubbleSort with the
> current ABCD. It removed all checks. IMHO, this is a good argument to
> prove that the issue is fixable without introducing principially new
> concepts.
>    

I disagree with your assessment.  I believe that although ABCD did work 
once, it is actually quite fragile.  My fix removes a major source of 
this fragility.

And as for introducing new concepts, I believe that has already happened 
when you decided to introduce an e-SSA that has enhanced pi nodes and 
that is used for both the upper bound and lower bound problems 
simultaneously.  I think those were good changes based on sound 
understanding.  I believe my change also falls into this category.  
Please take the time to understand what I am proposing.

Naveen

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