RFR(M): 8031754: Type speculation should favor profile data from outermost inlined method

[Krystal Mok]

Hi Vladimir,

My wild guess is that the outermost method generally gives you the best
(cleanest) context information. The inner callees may have been called from
various callers, and so their type profiles may have been polluted by other
callers.

- Kris


On Wed, Jan 22, 2014 at 7:51 PM, Vladimir Kozlov <vladimir.kozlov at oracle.com
> wrote:

> Roland,
>
> I don't see how inlining depth can define type's accuracy in general case.
> why it can't be reverse: more accurate type from most deeply inlined method?
>
> I thought you only have speculative type if it is the only one type record
> in MDO. How in your case you can have different types?
>
> Can you be more specific?
>
> Thanks,
> Vladimir
>
>
> On 1/22/14 1:42 AM, Roland Westrelin wrote:
>
>> When a node already has a speculative type, and parsing encounters extra
>> profiling data, the new profiling data is ignored. So profiling data coming
>> from profile points closer to the root of the compilation is favored which
>> I think makes sense: it's the data that is most specific to the context of
>> this compilation.
>>
>> During runs, profile data is not always entirely coherent so we may hit
>> something like this:
>> m1() {
>>     m3();
>> }
>>
>> m() {
>>    m1();
>>    m2();
>> }
>>
>> With: m3() and m2() have profile data for the same node. The first
>> profile data to be encountered during parsing is from m3() and profile data
>> from m2() is ignored but profile data from m2() is the one that is actually
>> the most specific and is the one that should be favored.
>>
>> When a speculative type is created, this change records the inline depth
>> at which the profile point is. The inline depth is then propagated together
>> with the rest of the type information. When new profile data is available
>> for a node that already has a speculative type, the current inline depth
>> and the inline depth of the current speculative type are used to decide
>> whether the new data should be used to replace the existing speculative
>> type.
>>
>> This change helps stabilize performance with nashorn.
>>
>> http://cr.openjdk.java.net/~roland/8031754/webrev.00/
>>
>> Roland.
>>
>>
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