Request for reviews (S): 7042327: assert(opaq->outcnt() == 1 && opaq->in(1) == limit) (original) (raw)

Vladimir Kozlov vladimir.kozlov at oracle.com
Thu May 5 19:10:10 PDT 2011

Thank you, Tom

I ran into small problem with last fix during Match because one IfNode has Con as condition but was not optimized out. I added the missing push to IGVN worklist in adjust_check() and updated webrev. It happened because Opaque2 node I added prevented constant propagation early. So I want to add Identity() to Opaque2 node but would like to get your opinion before I do this. Opaque2 node was originally (before this fix) used only for guarding loop's trip-counter. But with my change the limit expression could be transformed into constant or final value of trip-count could be transformed to constant if loop was empty. So I think it is safe to do this Identity transformation since it is not trip-count any more. What do you think?

+Node *Opaque2Node::Identity( PhaseTransform *phase ) {

Thanks, Vladimir

Tom Rodriguez wrote:

Looks good.

tom On May 5, 2011, at 5:30 PM, Vladimir Kozlov wrote:

Thank you, Tom

Thinking about what you said and, yes, such situation could happen. To be safe I need always put Opaque2 for limit for unrolled loop. I updated webrev. Thanks, Vladimir Tom Rodriguez wrote: It seems ok. Can't this situation occur as a result of other optimizations? If limit is behind by some expressions that later gets optimized away it seems like the same configuration could happen. Or isn't that possible? tom On May 5, 2011, at 4:03 PM, Vladimir Kozlov wrote: http://cr.openjdk.java.net/~kvn/7042327/webrev

Fixed 7042327: assert(opaq->outcnt() == 1 && opaq->in(1) == limit) New loop unrolling code calculate newlimit = limit-stride. If limit is trip-counter (phi+stride) with the same stride from a previous loop then newlimit will be optimized to pre-incremented value: newlimit = phi. reorgoffsets() optimization will create a separate Opaque2 node for each use of trip-counter (phi) and as result zero trip guard limit will be different from loop limit and it causes the assert to fail. Separate limit by Opaque2 node when calculating new limit for unroll if limit is an incremented variable from previous loop to avoid using pre-incremented value and reduce register pressure. I also removed code which creates dead loops since limit is input to newlimit. Tested with failed case and CTW.

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