RFR: 8372591: assert(!current->cont_fastpath() || freeze.check_valid_fast_path()) failed

[Richard Reingruber]

On Thu, 18 Dec 2025 00:02:46 GMT, Richard Reingruber <rrich at openjdk.org> wrote:

> > @reinrich @TheRealMDoerr Could you verify if this fix is correct for ppc too? Thanks.
> 
> The fix looks correct. Strangely the reproducer didn't work on ppc. Not even with 3x the locals in the osr method. I'll look a little more into it...

On ppc we reach `OSR_migration_begin` with `_cont_fastpath` that's higher than `sender.sp()` so `push_cont_fastpath(sender.sp())` has no effect.
I'm not sure why this is. It might be due to the trimming with i2i calls where the sender is trimmed to a `parent frame` (the top frame always has room for max_stack). The sender is a lambda. Maybe it has done an i2c call as `top frame` (i.e. untrimmed) which set `_cont_fastpath`?

If max_stack of the sender is very large then, due to trimming, unextended_sp < sp is possible and the assertion could also fail.

Maybe the maximum of unextended_sp and sp could be used?

Note that on ppc frame::id() returns the fp. Maybe this should be used as `_cont_fastpath`. Needs more investigation...

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PR Comment: https://git.openjdk.org/jdk/pull/28830#issuecomment-3671801749