JEPs proposed to target JDK 9 (2016/10/19)

[Christian Thalinger]

> On Oct 19, 2016, at 12:51 PM, Vladimir Kozlov <vladimir.kozlov at oracle.com> wrote:
> 
> On 10/19/16 3:31 PM, Vitaly Davidovich wrote:
>> 
>> 
>> On Wednesday, October 19, 2016, John Rose <john.r.rose at oracle.com <mailto:john.r.rose at oracle.com>
>> <mailto:john.r.rose at oracle.com <mailto:john.r.rose at oracle.com>>> wrote:
>> 
>>    On Oct 19, 2016, at 3:11 PM, Vitaly Davidovich <vitalyd at gmail.com
>>    <javascript:_e(%7B%7D,'cvml','vitalyd at gmail.com');>> wrote:
>>> 
>>>    I think David must be talking about stripping the binary to just
>>>    the set of methods known to be used - think of internal linkage,
>>>    like static functions in C which may just get inlined and aren't
>>>    present in the binary.  So in Java AOT, closest parallel would be
>>>    a private method but of course that's callable at runtime, so I
>>>    don't see how AOT can just omit it entirely.
>> 
>>    AOT supports deoptimization and re-JIT-ing, so it would be easy to
>>    omit methods from AOT output, and just use interpreter or JIT to
>>    handle the execution.
>> 
>> This would have to be opt-in, I'd imagine, as otherwise it would defeat
>> the purpose of AOT.  Or it would have to very limited where it does this.
> 
> re-JIT-ing (generating profiling code in AOT methods) is triggered by --compile-for-tiered flag. By default is off.
> But AOT code is following the same deoptimization rules as normal JITed code. For example, class unloading or redefinition.
> 
>> 
>> Separately, what optimizations (if any) will be done in AOT? Clearly
>> there's no profiling info, which is where the big gains typically come
>> from, but will anything be done? For example, are loops optimized
>> (unrolled, unswitched, etc)? Are statically known (at AOT time) callees
>> inlined? Or is it basically C1 level of optimization (i.e. very minimal)?
> 
> Currently it is C1 level only or even less - based on CHA without profiling information. We may add profiling information feedback in a future.
> No C2 type loop optimizations - Graal-core does some but not all.
> Also in tiered mode AOT code contains profiling code similar to Tiered level 3 in current Tiered compilation.

I think you mean level 2 (unless something changed since I left).

> AOT code is immutable - have to do indirect klass loads and calls.
> Also klass loading in AOT code is lazy - it has dynamic checks for class loading.
> 
> In short - do not expect good peak performance from current AOT code. That is why we added --compile-for-tiered to re-JIT to get peak performance.
> 
> We bet on compiled static initializers and skipping Interpreter for startup improvement.
> 
> Vladimir
> 
>> 
>> 
>>    AOT could do stuff like tree shaking (static call graph
>>    minimization) or enforcement of strong encapsulation, but it doesn't
>>    yet.  It's early days for this technology.
>> 
>> 
>>    — John
>> 
>> 
>> 
>> --
>> Sent from my phone