RFR: 8335392: C2 MergeStores: enhanced pointer parsing [v18]

[Emanuel Peter]

On Tue, 5 Nov 2024 23:38:59 GMT, Shaojin Wen <swen at openjdk.org> wrote:

> Currently, TraceMergeStores can only be used in fastdebug images. Are you planning to support it in release images?

I generally don't support it in release builds, only debug - or rather `NOT_PRODUCT`. The issue with supporting in release is that some other printing methods I use are not available in product (`Node::dump`). And if we support it in release, then we have to create a CSR, clearly specify what it prints, and then we are going to be less flexible in the future with changing the behavior. So I would rather not make it product, at least for now ;)
BTW: this is also why you can only disable `-XX:-MergeStores` with `-XX:+UnlockDiagnosticVMOptions `: it is not a full product flag, and so does not require a CSR, and we are able to remove it or change its behavior. But if someone really has an issue with the MergeStores optimization, they at least have a workaround until we are able to fix it ;)

Does that make sense?

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PR Comment: https://git.openjdk.org/jdk/pull/19970#issuecomment-2458892679