RFR: 8377658: G1: Cleanup g1ConcurrentMark.cpp for stricter warning flags

[Leo Korinth]

On Thu, 12 Feb 2026 20:16:58 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

>> Cleanup `g1ConcurrentMark.cpp` and included header files to remove implicit narrowing conversions.
>> 
>> For gcc: `-Wconversion -Wno-float-conversion`
>> For clang: `-Wimplicit-int-conversion`
>> 
>> `sizeof_auto` is created so that we can reduce the amount of casting and thus make the code more type safe. The normal `sizeof` will return a `size_t` although the size of most stuff can be represented in a `uint8_t`. `sizeof_auto`  will return the size in an as small unsigned type as is possible. The result is that expressions that uses `sizeof_auto` can convert to most integral types, and no explicit narrowing cast will be needed.
>
> src/hotspot/share/gc/g1/g1RegionMarkStatsCache.hpp line 101:
> 
>> 99: 
>> 100:   uint hash(uint idx) {
>> 101:     return idx & static_cast<uint>(_num_cache_entries_mask);
> 
> It looks like `_num_cache_entries_mask` could be changed to an `uint` instead.

Yes, that is much better, I will change it to a `const uint`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/29701#discussion_r2804155791