RFR: 8323582: C2 SuperWord AlignVector: misaligned vector memory access with unaligned native memory [v4]

Wed Feb 26 10:30:15 UTC 2025

On Wed, 26 Feb 2025 10:15:48 GMT, Roland Westrelin <roland at openjdk.org> wrote:

> > And would we not have similar issues with traversing from the loops to their `OpaqueMultiversioningNode`? What if some are not reachable in the meantime? Then we would just lose the `multiversion_if` early, and could not use it any more. So maybe we'd have to do that after the verification: [JDK-8350637](https://bugs.openjdk.org/browse/JDK-8350637): C2: verify that main_loop finds pre_loop and that multiversion loops find the multiversion_if
> > I wonder if we do not have similar issues with `PhaseIdealLoop::eliminate_useless_zero_trip_guard()` currently. Maybe it's rare enough we don't notice.
> 
> I don't think that's a problem. When that code runs the graph is in a stable shape. There's no dead condition that needs to go through igvn to be cleaned up. We've just run igvn and haven't made any change to the graph yet.

Ah ok, I'll have to look into it myself then. But if we know that it happens at the beginning of a loop-opts phase just after igvn, and no predicates were hacked yet, then that should work fine.

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PR Comment: https://git.openjdk.org/jdk/pull/22016#issuecomment-2684550571