MaxRecursiveInlineLevel oddity

[Christian Thalinger]

On Apr 28, 2011, at 7:56 PM, Vladimir Kozlov wrote:
> 6552561: MaxRecursiveInlineLevel flag doesn't operate correctly

Ohh, great.  I will send out a webrev.  -- Christian

> 
> Tom Rodriguez wrote:
>> I believe there's actually a bug already filed about this.  It will certainly change the results of the inlining in rare cases but it seems reasonable to may it consistent.
>> tom
>> On Apr 28, 2011, at 6:38 AM, Christian Thalinger wrote:
>>> While looking at JRuby performance and thus assembly code I noticed an oddity with recursive inlining:
>>> 
>>> $ java -XX:CICompilerCount=1 -XX:+PrintCompilation -XX:+PrintInlining -XX:MaxRecursiveInlineLevel=0 fib
>>> VM option 'CICompilerCount=1'
>>> VM option '+PrintCompilation'
>>> VM option '+PrintInlining'
>>> VM option 'MaxRecursiveInlineLevel=0'
>>>   340    1             fib::fib (21 bytes)
>>>                           @ 10   fib::fib (21 bytes)   inline (hot)
>>>                             @ 10   fib::fib (21 bytes)   recursively inlining too deep
>>>                             @ 16   fib::fib (21 bytes)   recursively inlining too deep
>>>                           @ 16   fib::fib (21 bytes)   inline (hot)
>>>                             @ 10   fib::fib (21 bytes)   recursively inlining too deep
>>>                             @ 16   fib::fib (21 bytes)   recursively inlining too deep
>>>   362    1 %           fib::main @ 2 (21 bytes)
>>>                           @ 10   fib::fib (21 bytes)   inline (hot)
>>>                             @ 10   fib::fib (21 bytes)   recursively inlining too deep
>>>                             @ 16   fib::fib (21 bytes)   recursively inlining too deep
>>> 
>>> It seems there is a "bug" in the logic in that it doesn't take the compiled method into account when counting the recursive inlining depth.  I expected when using MaxRecursiveInlineLevel=0 that there is no recursive inlining at all.
>>> 
>>> The simple example above shows that it might be possible that there are performance jumps between the various compiled methods as the recursive inlining depth changes.
>>> 
>>> I'd like to fix that (and I already have a fix that handles direct and indirect recursion) but the question is can we fix that given the possibility that it can change performance of applications?
>>> 
>>> -- Christian