RFR: 8345287: C2: live in computation is broken

[Roberto Castañeda Lozano]

On Tue, 3 Dec 2024 12:51:57 GMT, Roberto Castañeda Lozano <rcastanedalo at openjdk.org> wrote:

> Test results on Oracle CI look good, benchmarks are still running but the results look rather neutral so far.

Benchmarking is done now, the results of applying this changeset are as follows:
- neutral for DaCapo (bach and chopin)
- slight overall regression for Renaissance
- one slight improvement (crypto.signverify, around +1%) and one noticeably regression (scimark.monte_carlo, around -5%) for SPECjvm2008 on a Coffee Lake-B processor (3.0 GHz Intel Core i5-8500B).

Given these results, I think it might be good to investigate what is the overall effect of `OptoRegScheduling` and whether it makes sense to keep it enabled for x64 before integrating this fix. The opposite order (integrating and then investigating how to deal with the regressions) seems like a higher-risk approach. @rwestrel @vnkozlov @dean-long what do you think?

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PR Comment: https://git.openjdk.org/jdk/pull/22473#issuecomment-2519472283