[foreign-jextract] RFR: 8277830: jextract generated code should not depend on Java layouts

[Jorn Vernee]

On Mon, 29 Nov 2021 14:58:28 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> This patch tweaks jextract generation, so that a new constant class is emitted, namely `Constant$root`, which contains the definition of all basic C primitive types. These are declared with the correct alignment constraints, depending on platforms.
>> 
>> Every other layout created by jextract will depend on these shared layouts constants, so that jextract code doesn't depend on alignment choices in `ValueLayout` constants.
>> 
>> In the future, we should probably generalize this approach, so that e.g. layouts are emitted only once, and then referred to afterwards - not just for primitive types, but also for everything else (struct, typedef, etc.). This would minimize the amount of layouts we store in the constant classes.
>
> src/jdk.incubator.jextract/share/classes/jdk/internal/jextract/impl/ToplevelBuilder.java line 245:
> 
>> 243:                 return "JAVA_CHAR.withBitAlignment(" + vl.bitAlignment() + ")";
>> 244:             } else if (vl.carrier() == byte.class) {
>> 245:                 return "JAVA_BYTE";
> 
> What about hyper-aligned bytes and booleans? Don't we always need a call to `withBitAlignment` ?

Ah I guess this code is only called from the methods below.

-------------

PR: https://git.openjdk.java.net/panama-foreign/pull/620