RFR: 8343800: Cleanup definition of NULL_WORD

[David Holmes]

On Sun, 1 Dec 2024 07:54:49 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> Please review this change to how NULL_WORD is defined.  Instead of being a
> macro whose definition is in compiler-specific files with a conditionally
> defined expansion, it is now a simple integral constant with a single shared
> definition.
> 
> Testing: mach5 tier 1-5, GHA sanity tests.

Marked as reviewed by dholmes (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/22468#pullrequestreview-2472506619