Assembly output from JRuby 'fib'

[Christian Thalinger]

On Apr 28, 2011, at 3:19 PM, Charles Oliver Nutter wrote:
> On Thu, Apr 28, 2011 at 5:16 AM, Christian Thalinger
> <christian.thalinger at oracle.com> wrote:
>> I took a look at it.  I used 64-bit x86 since the code is a bit smaller than with 32-bit.
>> 
>> The code is almost identical but three things popped into my eye (the output is from PrintOptoAssembly):
>> 
>> 1. The obvious one:  the method handle call site guard:
>> 
>> 1a4   B32: #    B160 B33 <- B31 B149 B123  Freq: 0.499969
>> 1a4     movq    R10, byte[int:>=0]<ciObject ident=770 PERM address=0xe99088> *  # ptr
>> 1ae     movq    R10, [R10 + #1576 (32-bit)]     # ptr
>> 1b5     movq    R11, [R10 + #32 (8-bit)]        # ptr
>> 1b9     movq    R8, java/lang/invoke/AdapterMethodHandle:exact *        # ptr
>> 1c3     cmpq    R11, R8 # ptr
>> 1c6     jne,u  B160  P=0.000000 C=-1.000000
> 
> I saw in your other email that eliminating this puts indy on par with
> dynopt, which is spectacular news. Can you elaborate on how that would
> be possible to do "correctly" (as in not via a hack)? Would it be a
> lighter-weight check and deopt of some kind (in Hotspot), or is it
> something I'd need to rig up on my code?


This would be what we referred to in the past as pull-vs-push notification.  I don't have details about that yet but maybe John has already thought this through and has an implementation idea (or even details).  Not sure when get around to implement that.

-- Christian