RFR: 8365053: Refresh hotspot precompiled.hpp with headers based on current frequency [v3]

[Francesco Andreuzzi]

On Fri, 8 Aug 2025 06:23:43 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> Francesco Andreuzzi has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   script. update
>
> src/utils/PrecompiledHeaders/PrecompiledHeaders.java line 70:
> 
>> 68:         // Count inclusion times for each header
>> 69:         Map<String, Integer> occurrences = new HashMap<>();
>> 70:         try (Stream<Path> paths = Files.walk(hotspotPath)) {
> 
> I think walking the source tree is the wrong approach to gathering the data
> about include counts. I think better is to do a build and then look at the
> files <builddir>/hotspot/variant-server/libjvm/objs/*.d. From that one can build
> a completely accurate count of the transitive inclusions.

I followed this hint, the latest version of the script checks the `.d` files. 

Two observations:
- The magic number is now `2460` (more includes are taken into account, which makes sense)
- There is much less wiggle room, 2461 includes nothing, 2459 includes too much
- Runtime does not seem to be affected negatively or positively

If anybody is interested, this file contains the inclusion count for each source file: [inclusions_count.txt](https://github.com/user-attachments/files/21682561/inclusions_count.txt)

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PR Review Comment: https://git.openjdk.org/jdk/pull/26681#discussion_r2262707516