RFR: 8339242: Fix overflow issues in AdlArena [v4]

[Kim Barrett]

On Thu, 5 Sep 2024 20:21:20 GMT, Dean Long <dlong at openjdk.org> wrote:

>> Casper Norrbin has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   review suggestions
>
> src/hotspot/share/adlc/adlArena.cpp line 141:
> 
>> 139: 
>> 140: //------------------------------realloc----------------------------------------
>> 141: size_t pointer_delta(const void *left, const void *right) {
> 
> Do we want to assert left >= right here?

It's currently only used in one place, where we know that's true.  OTOH, an assert doesn't hurt.
Instead of this helper function, we could just use`(size_t)(_max - c_old)` inline (we can be
confident the difference won't exceed the `ptrdiff_t` range here), reducing the lines of code by
a little bit.  The benefit from the helper is having the Arealloc code (nearly? completely?) identical
here and in memory/arena.cpp.  I don't have a strong opinion either way.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20774#discussion_r1746467080