RFR: 8340620: Fix -Wzero-as-null-pointer-constant warnings for CompressedOops

[Kim Barrett]

On Thu, 26 Sep 2024 09:21:39 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

> FWIW, I think these asserts adds extra noise to these functions and I don't think we will be much more happy about having to read them over and over again when we read this functions / debug code through these functions. I would have preferred if this was one of those things that we require from our platforms and place a check in globalDefinitions, or some other prominent place that checks HotSpot's assumptions of the compilers / platforms.

Implementing option 2 (making base() an integral offset) would remove that
assumption here, and allow removal of the assertions currently proposed here.
And I generally prefer placing asserts with the expecting code. OTOH, I think
it's nearly certain there are other places where we make the same assumption.
(And I'd forgotten we have some assumption checks in globalDefinitions.cpp.)
I don't have a strong opinion in this area.

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PR Comment: https://git.openjdk.org/jdk/pull/21172#issuecomment-2376711459