RFR: jextract generates BigDecimal for "long double" but binder fails to handle it

[Sundararajan Athijegannathan]

Looks good.

-Sundar

On 05/11/18, 8:08 PM, Maurizio Cimadamore wrote:
> Updated webrev:
>
> http://cr.openjdk.java.net/~mcimadamore/panama/8213029_v3
>
> Thanks for the comments
>
> Maurizio
>
> On 05/11/2018 10:27, Maurizio Cimadamore wrote:
>> Hi,
>> this patch adds support for X87 values in the binder
>>
>> http://cr.openjdk.java.net/~mcimadamore/panama/8213029/
>>
>> The Hotspot changes are straightforward; there's a new X87 shuffle 
>> recipe category which needs to be taken into account (its size is 128 
>> bits). Changes are needed on the binder side too as the X87 arguments 
>> have to be properly classified.
>>
>> More specifically, the ABI is very subtle when it comes to 'complex' 
>> values; they are generally passed in stack slots (if they are in 
>> argument position) but they are passed in registers (X87 st0 for 
>> 'long double' or both 'st0' and 'st1' for 'long double complex') for 
>> return values. To achieve this, we need to teach the binder about the 
>> special LongDoubleComplex struct, so that the right classification 
>> occurs (see changes to CallingSequenceBuilderImpl).
>>
>> Another issue is how to handle X87 values in Java - I started out 
>> trying to map these values to BigDecimal, but after getting it to 
>> work I realized that there were too many unanswered questions: one 
>> performance side, to decode an X87 value into a BigDecimal you have 
>> to create lots of intermediate BigIntegers/BigDecimal; on the 
>> expressiveness side, BigDecimal is lacking support for NaN/Infinity, 
>> making it an improper fit.
>>
>> I then decided to 'erase' X87 values down to 'double' (using a JNI 
>> helper function to do the conversion, which should be efficient as it 
>> can take advantage of platform specific instructions such as flstp 
>> etc.).
>>
>> I tested it with fast-debug to make sure there were no weird hotspot 
>> failures, but please give it a spin to make sure it all works.
>>
>> I also updates existing complex tests to add more cases and upcall 
>> support.
>>
>> Cheers
>>
>> Maurizio
>>
>>
>>