RFR: 8327963: C2: fix construction of memory graph around Initialize node to prevent incorrect execution if allocation is removed [v8]

[Roberto Castañeda Lozano]

On Thu, 12 Jun 2025 15:39:35 GMT, Roland Westrelin <roland at openjdk.org> wrote:

> One way would be to simply assert that there's no `NarrowMemProj`s left during final graph reshape. Is that what you'd like?

Yes, that would be great (and I think it is OK to leave it to a future RFE if fully enforcing it would further increase the complexity of this PR).

> Stepping back, what's the concern here? The new projections should mostly be harmless.

I do not have any concrete concern in mind, I just think it would be good to limit the number of C2 components that might be affected by this change, in this case the back-end. One can never be totally confident that there is no fragile analysis relying on hidden assumptions about the shape of the memory graph (in this case, single memory projections).

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PR Comment: https://git.openjdk.org/jdk/pull/24570#issuecomment-2969607350