[foreign+linkToNative] RFR: Fill out missing Windows upcall stub generation

[Sundararajan Athijegannathan]

Incremental webrev looks good to me.

-Sundar

On 12/02/19, 6:57 PM, Jorn Vernee wrote:
> Thanks for bringing this up.
>
> I remember seeing that JEP discussed on build-dev a while ago, so I 
> thought trying out constexpr (a C++11 feature) and thought the 
> compiler would reject it if usage was not yet allowed by the build 
> system. e.g. through a flag like -std=c++03.
>
> But, reading more into it now, it looks like such a flag is only 
> supported since MSVC 2017, and the minimal setting is C++14 [1].
>
> From the JEP it seems that use of `constexpr` is not officially 
> allowed yet. What I added can be changed to use `const`. I was using 
> constexpr to make sure I had a constant expression to declare the 
> array in upcall_context, but the compiler will also throw an error if 
> the expression is not constant, so it's not super important.
>
> I have tested the following patch, which should fix the issue: 
> http://cr.openjdk.java.net/~jvernee/panama/webrevs/constexprfix/webrev.00/
>
> Jorn
>
> [1] : 
> https://docs.microsoft.com/en-us/cpp/build/reference/std-specify-language-standard-version?view=vs-2017
>
> Sundararajan Athijegannathan schreef op 2019-02-12 06:36:
>> This is in response to
>> https://mail.openjdk.java.net/pipermail/panama-dev/2019-February/004199.html 
>>
>>
>> Change in directUpcallHandler_x86.cpp uses "constexpr".
>>
>>     https://openjdk.java.net/jeps/347 (a candidate JEP)
>>
>> says
>>
>> " With JDK 11, the code has been updated to support building with
>> newer versions of the C++ standard, although it is not yet using any
>> new features. This includes being able to build with recent versions
>> of various compilers that support C++11/14 language features."
>>
>> FWIW I searched for "constexpr" in current hotspot code and I didn't
>> find any usage.
>>
>> -Sundar