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

[Casper Norrbin]

On Fri, 6 Sep 2024 03:29:43 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> 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.

The motivation was to keep the two arenas consistent. To that end, I've now added an assert and made the function static.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20774#discussion_r1746740935