RFR: 8310906: Fix -Wconversion warnings in runtime, oops and some code header files.

[Coleen Phillimore]

On Tue, 27 Jun 2023 12:59:59 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

>> This is another version of PR https://github.com/openjdk/jdk/pull/14659 but I've added a pointer delta function in globalDefinitions.hpp to use for these pointer diff calculations that return int everywhere.  If the name is agreeable, I'll fix the other cases of this like this.  It's better than raw casts.
>> Tested with tier1-4.
>
> src/hotspot/share/code/codeBlob.inline.hpp line 36:
> 
>> 34: inline const ImmutableOopMap* CodeBlob::oop_map_for_slot(int slot, address return_address) const {
>> 35:   assert(_oop_maps != nullptr, "nope");
>> 36:   return _oop_maps->find_map_at_slot(slot, delta_as_int((intptr_t) return_address, (intptr_t) code_begin()));
> 
> Is this the only usage of `delta_as_int` that operates on `intptr_t`? If we remove the casts then all usages would operate on pointers. Maybe this is an indication that we only need a `pointer_delta_as_int` function, to go hand in hand with the other `pointer_delta` functions?

Hm.  Maybe this would be ok. Our original idea was to make it T* not T until this cast.  I don't know how many other cases there are that I haven't gotten to yet.  But it would eliminate a cast, so that's good (unless these aren't the same).  Some instances have ptr - constant that gets promoted I think.
The reason we didn't pick pointer_delta_as_int because pointer_delta has different semantics.  pointer_delta insists on positive results.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14675#discussion_r1243892244