JEPs proposed to target JDK 9 (2016/10/19)
vladimir.kozlov at oracle.com
Wed Oct 19 22:51:18 UTC 2016
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>> wrote:
> On Oct 19, 2016, at 3:11 PM, Vitaly Davidovich <vitalyd at gmail.com
>> 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
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.
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
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
> 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
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