RFR(S): 8193927: Optimize scanning code for oops.

[Lindenmaier, Goetz]

Hi Volker, 

> looks good now! Thanks for doing the change.
thanks!

> I'm pretty sure you could return 'false' on zero as well as zero
> doesn't generate any code at all.
If there are no nmethods, the returned value of the function
is pointless on zero.

Best regards,
  Goetz.



> 
> Regards,
> Volker
> 
> 
> On Thu, Dec 21, 2017 at 5:18 PM, Lindenmaier, Goetz
> <goetz.lindenmaier at sap.com> wrote:
> > Hi Volker,
> >
> > you are right, encapsulating it in a function is a better solution:
> > http://cr.openjdk.java.net/~goetz/wr17/8193927-oopsInCode/webrev.02
> >
> > Making it switchable would require changes to x86, which is
> > not my scope.
> >
> > Best regards,
> >   Goetz.
> >
> >> -----Original Message-----
> >> From: Volker Simonis [mailto:volker.simonis at gmail.com]
> >> Sent: Donnerstag, 21. Dezember 2017 14:51
> >> To: Lindenmaier, Goetz <goetz.lindenmaier at sap.com>
> >> Cc: hotspot-compiler-dev at openjdk.java.net
> >> Subject: Re: RFR(S): 8193927: Optimize scanning code for oops.
> >>
> >> Hi Goetz,
> >>
> >> this seems to be a little strange flag for me because it can not be
> >> used for really controlling the emission of immediate oops. It only
> >> records if a platform can emit immediate oops or not.
> >>
> >> So wouldn't it be better to either have a flag like
> >> "EmitImmediateOops" which really controls the emission of immediate
> >> oops. I.e. it could be used to switch the emission of immediate oops
> >> off even on platforms which usually do that. Or if that's not
> >> reasonable, don't introduce a new flag at all but just declare a
> >> platform specific method instead which returns if immediate oops can
> >> be emitted on that platform or not.
> >>
> >> Thanks,
> >> Volker
> >>
> >> On Thu, Dec 21, 2017 at 9:30 AM, Lindenmaier, Goetz
> >> <goetz.lindenmaier at sap.com> wrote:
> >> > Hi,
> >> >
> >> > Some platforms don't emit immediate oops to the code. If so, scans
> >> > of the code for oops can be skipped.
> >> >
> >> > Add flag ImmediateOopsEmitted to each platform specifying the
> behavior.
> >> > Only search code for immediate oops if this flag is set. Make sure no
> >> > oops are emitted to code if the flag is not set.
> >> >
> >> > @aarch people: should the flag set to 'false' on aarch/arm?  So far it
> >> > is true, which defaults to the old behavior.
> >> >
> >> > Please review this change. I please need a sponsor.
> >> > http://cr.openjdk.java.net/~goetz/wr17/8193927-
> oopsInCode/webrev.01/
> >> >
> >> > Best regards,
> >> >   Goetz