TraceTypeProfile as diagnostic option

[Nils Eliasson]

AFAIK, all verbose/trace/debug-print output should be available in 
product builds behind flag + diagnostic. It is such a time saver when 
you can use it directly, it simplifies the code, and can be very helpful 
when debugging in situations where product builds are required.

//N

Aleksey Shipilev skrev 2012-09-10 13:08:
> Hi,
>
> First, let me describe the rationale. When I'm looking into the
> disassembly, I use this command line to dump the generated assembly:
>
> -XX:+UnlockDiagnosticVMOptions -XX:+PrintAssembly -XX:+TraceTypeProfile
> -XX:+PrintCompilation -XX:+PrintInlining -XX:CICompilerCount=1
>
> This generates arguably human-readable output in the form:
>
>   for [each method]; do
>       [PrintCompilation prints single compile record]
>       [PrintInlining prints inlining tree]
>       [PrintAssembly dumps the disassembly]
>   done
>
> Soon enough I realize that bimorphic calls in inlining tree have
> arguably counter-intuitive form:
>
> 81   13             TestInline::doWork (56 bytes)
>     @ 35   TestInline$DelegatingIterator::next (10 bytes)   inline (hot)
>       @ 4   java.util.ArrayList$Itr::next (66 bytes)   inline (hot)
>       @ 4   TestInline$DelegatingIterator::next (10 bytes)   inline (hot)
>
> Naively-looking that might mean the $DelegatingIterator::next calls both
> next() methods in the code, but that is confusing because there is a
> single virtual call in the user code.
>
> Enabling -XX:+TraceTypeProfile helps a lot:
>
>    @ 35   TestInline$DelegatingIterator::next (10 bytes)   inline (hot)
>    \-> TypeProfile (128014/128014 counts) = TestInline$DelegatingIterator
>     @ 4   java.util.ArrayList$Itr::next (66 bytes)   inline (hot)
>     @ 4   TestInline$DelegatingIterator::next (10 bytes)   inline (hot)
>      \-> TypeProfile (29297/58595 counts) = TestInline$DelegatingIterator
>      \-> TypeProfile (29298/58595 counts) = java/util/ArrayList$Itr
>
> ...albeit being a bit misplaced.
>
> But here's the kicker: -XX:+TraceTypeProfile is only available in
> fastdebug build, and so I need to make additional step to figure this
> out. For my taste, tracing type profiles should instead be unlocked with
> -XX:+UnlockDiagnosticVMOptions. Are there any benefits of hiding this?
> If not, I would be happy to provide the patch bringing it on par with
> other diagnostic options.
>
> -Aleksey.