RFR(M): 8136725 Provide utility for creation a counted loop reserve copy (clone)

Vladimir Kozlov vladimir.kozlov at oracle.com
Mon Oct 5 08:07:44 UTC 2015

remove .hgtags changes

Trace outputs in create_reserve() are not under trace flag. I would 
suggest to remove them or put under TraceLoopOpts && Verbose combination.
Also, please, split next and similar lines according to our code stile:

if (!_lp_reserved->is_CountedLoop()) return false;
if (!_lp_reserved->is_CountedLoop()) {
   return false;

The rest looks fine.


On 10/1/15 4:31 AM, Igor Veresov wrote:
> Here’s the updated webrev:
> http://cr.openjdk.java.net/~iveresov/loop-reverse/webrev.02/
> igor
>> On Sep 28, 2015, at 2:25 AM, Civlin, Jan <jan.civlin at intel.com
>> <mailto:jan.civlin at intel.com>> wrote:
>> Vladimir,
>> Thank you for the review.
>> I'm attaching the patch reflecting your comments.
>> Regards,
>> Jan
>> -----Original Message-----
>> From: Vladimir Kozlov [mailto:vladimir.kozlov at oracle.com]
>> Sent: Wednesday, September 23, 2015 3:38 AM
>> To: Civlin, Jan; hotspot compiler
>> Subject: Re: RFR(M): 8136725 Provide utility for creation a counted
>> loop reserve copy (clone)
>> in loopUnswitch.cpp debug output should be under nonproduct flag
>> (could be TraceLoopOpts or separate new flag). Use #ifndef PRODUCT
>> around print code instead of repeated NOT_PRODUCT() macro. And I don't
>> think you need all output you added in final version.
>> All constants are IGVNed so you don't need to pre-generate const_0.
>> Since it is not connected to graph it could be eliminated.
>> And I don't think you need next for the same reason:
>>  311   lk->set_const_0(const_0);
>>  312   lk->set_const_1(const_1);
>> In ~CountedLoopReserveKit() and switch_to_reserved() you can make new
>> const_0 since you have pointer to IGVN:
>> _phase->_igvn.intcon(0);
>> You can't use subsume() since it will replace all users of const_1:
>> +    //TODO bug? could not use here _const_1->subsume_by(_const_0,
>> _phase->C);
>> It is correct to use set_req() for constants here.
>> superword.cpp I don't think you need to keep _CountedLoopReserveKit_test
>> code in final version after you verified it works during development:
>> +  //!///    Testing that switching to reserved copy works
>> Thanks,
>> Vladimir
>> On 9/19/15 1:05 AM, Civlin, Jan wrote:
>>> As I was working on modification of SuperWord::output - and this is a
>>> function where you modify the ideal graph on the fly and cannot exit
>>> on error - I was wondering how can I protect my algorithm in a case
>>> some wrong decision was made on the previous stage of the SuperWord
>>> but discovered only at the final stage, when the graph is already
>>> half modified.
>>> So here is my solution:
>>> - the graph to be modified is cloned.
>>> - five nodes are added: intcon(0) is disconnected, intcon(1)->If->
>>> IfTrue->orig_loop: IfFalse->clone_loop.
>>> Then any optimization is executed on the original loop, and if it
>>> finishes ok, nothing else need to be done, the clone_loop will be
>>> removed as dead in the consecutive stages of compiler.
>>> At any moment, if an error occurs, the node intcon(1) may be subsumed
>>> by node intcon(0), therefore  the clone_loop becomes "active" and the
>>> original "unfinished in modification" loop will be removed later.
>>> This utility is implemented in class CountedLoopReserveKit.
>>> The loop cloning and 5 nodes adding is realized in the ctor and
>>> possible subsuming intcon(1) by intcon(0) in dtor, so a simple return
>>> from the modifying graph function will do graph correction (switching
>>> in choice) of the graph.
>>> Basically, it is sufficient the create a local object of
>>> CountedLoopReserveKit class, the scoped dtor makes the choice:
>>> modified or original loop.
>>> SuperWord::output in this submission is included only to illustrate
>>> how to use the CountedLoopReserveKit.
>>> The actual new SuperWord::output where CountedLoopReserveKit  is
>>> indeed substantial is coming in the next patch.
>>> This reserve loop cloning in SuperWord may be disabled by the global
>>> flag DoReserveCopyInSuperWord.
>>> -----Original Message-----
>>> From: Igor Veresov [mailto:igor.veresov at oracle.com]
>>> Sent: Thursday, September 17, 2015 2:31 PM
>>> To: hotspot compiler
>>> Cc: Civlin, Jan
>>> Subject: RFR(M): 8136725 Provide utility for creation a counted loop
>>> reserve copy (clone)
>>> Provide utility for creation a counted loop reserve copy (clone).
>>> May be used in any graph optimization for simple roll back to the
>>> original loop, in partially will be used in SuperWord, where the loop
>>> modification goes on-the-fly and potentially may not finish correctly
>>> (the patch for SuperWord is coming soon).
>>> This is contributed by Jan Civlin <jan.civlin at intel.com
>>> <mailto:jan.civlin at intel.com>>
>>> Webrev: http://cr.openjdk.java.net/~iveresov/loop-reverse/webrev-091515/
>>> igor
>> <webrev-r9100r9092.tar.bz2>

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