RFR: 8327963: C2: fix construction of memory graph around Initialize node to prevent incorrect execution if allocation is removed

[Roland Westrelin]

On Wed, 23 Apr 2025 12:36:31 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>>> It would be great if we have union memory slices for this.
>> 
>> Something like that would fix it but it would be trickier to get right that this point fix, I think. Do you see any other use for it?
>
> @rwestrel You should update the bug title, it just sounds too generic. It is really helpful when the "blame" history gives you a helpful comment rather than `Umbrella` or `incorrect result` or some bug numbers.
> 
> I suggest `Use NarrowMemProj to project / split memory slice after Initialize`, but you probably have an even better idea ;)

@eme64 ready for another round of reviews when you have time

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PR Comment: https://git.openjdk.org/jdk/pull/24570#issuecomment-2883669669