Sorry for the delayed response. Clearly this is not my "day" job. :)
Responses are inline.
Egor Pasko wrote:
> On the 0x4F2 day of Apache Harmony Naveen Neelakantam wrote:
>
>> Would someone who understands the ABCD pass be willing to check my patch?
>>
>> Egor if you still follow the list, could you please take a look?
>>
>
> Naveen, again thanks for the great work!
>
> though I have some concerns about your patch:
>
> 1. changes in the solver are very unwanted because we want to make the
> solver as readable as possible (given that the concept is really
> complicated). Once we want equivalent Pi operands to behave like a
> single Pi operand, we should better link them together in the
> inequality graph (zeroedges, both higher and lower graphs). The
> solver goes through zero chains just fine.
>
I agree with the spirit of your comment, however in this case your
suggestion is infeasible. There are two alternatives as I see it, which
are dictated by the specifics of the algorithm. Either:
a) The upper bound and lower bound problems are solved using separate
eSSA graphs, or
b) The solver is modified to adopt the notion of piequivalence when
checking for termination conditions (and _only_ when checking for
termination conditions).
As a thought experiment, consider the implications of allowing zero
edges between pirenamed variables. It would essentially convey
constraints granted onto pirenamed variables upon their sources. This
would make it possible for sources to appear constrained by inequalities
that do _not_ dominate them. This is clearly incorrect.
In my opinion something must be done here, or ABCD should simply be
disabled as it is otherwise crippled.
Clearly this is a complicated problem, and I welcome argument. :)
> 2. "hvn,simplify,dce,uce,memopt,dce,uce"  hmm.. this is big change,
> may affect a lot. Does anybody run benchmarks these days to ensure
> we do not affect performance with this?
>
Can someone please comment on this? I too am very concerned about the
effect this might have on compilation speed.
> 3. "memopt" contains "hvn", is there really a reason to run it twice?
>
Probably not.
I will try removing hvn from the mix and see what happens. Thanks for
the heads up
>
>> Thanks,
>> Naveen
>>
>> Naveen Neelakantam (JIRA) wrote:
>>
>>> [drlvm][jit][abcd] classic abcd pass fixes
>>> 
>>>
>>> Key: HARMONY6007
>>> URL: https://issues.apache.org/jira/browse/HARMONY6007
>>> Project: Harmony
>>> Issue Type: Bug
>>> Environment: RHEL4, 32bit x86, gcc 4.1.2
>>> Reporter: Naveen Neelakantam
>>>
>>>
>>> The ABCD pass has effectively been crippled by changes that have been made to
DRLVM over the past year (I haven't been able to narrow down when the change happened).
>>>
>>> The good news is that with two simple fixes, ABCD works again. The attached
patch adds the necessary fixes.
>>>
>>> To see the problem however you can try running the bidirectional bubble sort
from HARMONY1564. It is wellknown that ABCD should be able to eliminate all the bounds
checks from the sort algorithm. However, if you run drlvm without this patch, none of the
bounds checks are eliminated. You can examine the logs by doing the following:
>>>
>>>
>>>> java XX:jit.p.filter=BidirectionalBubbleSort.sort XX:jit.p.arg.log=ct,irdump
Xem:server_static BidirectionalBubbleSort
>>>>
>>>>
>>> After applying the patch, all the bounds checks will once again be eliminated.
There were two separate problems to blame, which this patch addresses:
>>> 1) Harmony now inserts multiple "arraylen" operations when translating from bytecode,
even if the operation is redundant (because it postdominates an earlier "arraylen" operation
for the same array). This redundancy must be eliminated before running ABCD otherwise the
inequality graph that ABCD generates for its proofs will have unnecessary discontinuity.
Thankfully, solving the problem is as simple as running the following passes before ABCD:
"hvn,simplify,dce,uce,memopt,dce,uce".
>>> 2) Our implementation of ABCD includes a novel design by Egor Pasko where both
the upperbound and lowerbound problems can be solved using the same inequality graph. In
addition the implementation adds more constraints to the graph than the original ABCD authors
specified. Both improvements are correct, except that they can prevent the ABCD solver from
finding valid solutions because pirenamed variables appear to be different. The patch modifies
the solver so that it treats pirenamed variables as equivalent when checking for termination
conditions.
>>>
>>> I've verified that HARMONY2141, HARMONY2144, and HARMONY2147 still pass with
these changes.
>>>
>>>
>>>
>>
>
>
