[foreign-jextract] [Rev 02] RFR: 8239493: Add classfile generation to jextract

[Jorn Vernee]

> Hi,
> 
> This patch adds class file generation to jextract using ASM, which in some places replaces the generation done by the
> current source code generator. In particularly, it replaces the generation of all constant fields with static getters,
> that use dynamic constants as backing storage rather than fields. This allows for more sharing between constants, and
> also reduces the pressure on clinit code size a lot, enabling extraction of much bigger native header files. The new
> scheme generates an extra constant helper class which holds all these constants, and the source generator generates the
> high-level wrapper functions. The scheme can also be extended to generate multiple constant helper classes, should we
> run out of constant pool indices (in rare cases).  This patch reworks the interface of JavaSourceBuilder, since extra
> parameters are needed in order to do the new constant generation. For generating methods that need constants, it calls
> into a new ConstantHelper class, which returns a DirectMethodHandleDesc describing the generated constant getter. A
> call to this getter is then emitted.  This patch also merges the HandleSourceFactory and StaticWrapperSourceFactory
> into OutputFactory, since only the latter was ever being used, but the split in code made it a lot harder to reason
> about the correctness of for instance changing C identifiers into java-safe ones. Because of this, the diff for
> OuputFactory looks a bit messy, so maybe it's easier to look at the resulting file as a whole.  The tests are changed
> to look for the now generated static getters, instead of fields (`static final` fields don't work well with dynamic
> constants, since they are eagerly initialized).  As a small bonus, this patch adds the missing ABI-agnostic
> C_LONGDOUBLE constant (this was causing some test failures).  Thanks, Jorn

Jorn Vernee has updated the pull request incrementally with three additional commits since the last revision:

 - Addressed review comments:
   - Made Utils final, and added private constructor
   - renamed some addXXX methods in JavaSourceBuilder to addXXXGetter for clarity
   - renamed some getXXX method in JavaSourceBuilder to XXXGetCallString for clarity
   - renamed some visitedXXX methods in OutputFactory to XXXSeen for clarity
   - Factored out several calls to emitGetter in constantHelper into helper methods with more readable names
 - Remove makeCString bootstrap and depend on Cstring::toCString instead
 - Add class gen test

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

Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/102/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/102/files/517a9c72..aa60472b

Webrevs:
 - full: https://webrevs.openjdk.java.net/panama-foreign/102/webrev.02
 - incr: https://webrevs.openjdk.java.net/panama-foreign/102/webrev.01-02

  Stats: 586 lines in 8 files changed: 468 ins; 81 del; 37 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/102.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/102/head:pull/102

PR: https://git.openjdk.java.net/panama-foreign/pull/102