RFR: 8282024: add EscapeAnalysis statistics under PrintOptoStatistics [v14]

[Vladimir Kozlov]

On Sat, 21 May 2022 15:52:09 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> In previous revision, @aamarsh used 3 data members of Compile.  This tuple is a snapshot. 
>> 
>> 
>> _local_no_escape_ctr
>> _local_arg_escape_ctr
>> _local_global_escape_ctr
>> 
>> 
>> ConnectionGraph::escape_state_statistics() initializes them all zeros and categorize Java objects of the connection graph. 
>> 
>> here is the framework. 
>> 
>>    do {
>>         EscapeAnalysis();
>>         MacroExpand.eliminate_macro_nodes();      
>>     } while (progress?);
>> 
>> #ifndef PRODUCT
>>     Atomic::add(&ConnectionGraph::_no_escape_counter, _local_no_escape_ctr + total_scalar_replaced);
>>     Atomic::add(&ConnectionGraph::_arg_escape_counter, _local_arg_escape_ctr);
>>     Atomic::add(&ConnectionGraph::_global_escape_counter, _local_global_escape_ctr);
>> #endif
>> 
>> Both you and @JohnTortugo  pointed out that there was a bug in previous revision. We overlook that non-escaped objects are double-counted in last iteration. I think it's amendable.  
>> 
>> I call this snapshot approach because it uses the snapshot of last iteration to update global statistical counters.  all intermediate snapshots are drop. Allow me to write down @aamarsh 's approach. 
>> 
>> The number of Java object `JO` is from user-program by nature.  EscapeAnalysis breaks them down into 3 categories. non-escaped, arg-escaped and global escaped.  Without iterative EA, we can report this snapshot to statistical counters.
>> 
>> With iterative EA, a problem arise. Some objects elided in  previous iteration of MacroExpansion. if we use last snapshot, we have to add those eliminated java objects. Let's say iterative EA iterates N times in total. `E` is the number of eliminated java object from 1 to N-1 iterations (exclude the last iteration here).  
>> 
>> Since all eliminated objects must be non-escaped, so we add E back to _no_escape_counter. We account for all java objects of this compilation unit.  
>> 
>>     Atomic::add(&ConnectionGraph::_no_escape_counter, _local_no_escape_ctr + E);
>>     Atomic::add(&ConnectionGraph::_arg_escape_counter, _local_arg_escape_ctr);
>>     Atomic::add(&ConnectionGraph::_global_escape_counter, _local_global_escape_ctr);
>> 
>> 
>> In this way, We keep track of all java objects of this CU  for iterative EA. I think it's accurate. 
>> 
>> JO = _local_no_escape_ctr + E + _local_arg_escape_ctr  + _local_global_escape_ctr
>> 
>> 
>> I suggest to hoist the variable `PhaseMacroExpand mexp` out of loop and make it stateful to track E.
>
> Got it. Thank for explaining - you simply used data from last iteration.
> I think you can do similar with much less complexity if you used data from **first** iteration and current code change:
> 
> void ConnectionGraph::escape_state_statistics(GrowableArray<JavaObjectNode*>& java_objects_worklist) {
>   if (!PrintOptoStatistics || (_invocation > 0)) { // Collect data only for first invocation
>     return;
>   }
>   for (int next = 0; next < java_objects_worklist.length(); ++next) {

You need to revert `escape_state_statistics` back to non static for this of cause.

-------------

PR: https://git.openjdk.java.net/jdk/pull/8019