perf: ZTS: move AG and SCNG into native __thread storage, replay of #22231

[henderkes]

So I largely copied the approach of #22231, but this time for AG and SCNG, because they're small in size (256 bytes, so we don't step back into the TLS surplus issue) and I don't need to touch the JIT.

EG and CG are "fine" to keep in the heap storage with the const offsets, because EG is mostly hot in dispatch and the __thread symbol is already kept loaded in the hybrid VM. For clang compile-heavy code still suffers a bit from tsrm_ls_cache base reloads, but I'm still brainstorming for that.

This mostly benefits the lexer and allocations.

@arnaud-lb

[arnaud-lb]

/* A __thread block of a foreign thread is inaccessible. */

Is that because the thread may not exist anymore, or is there another reason?

We need to ensure that shutdown_memory_manager(CG(unclean_shutdown), 1); is called in php_module_shutdown. Currently we avoid calling it in ZTS builds because we rely on the TSRM dtor, I believe.

I would go as far as removing the dtor argument from ts_allocate_tls_id since it's not going to be called for most threads during tsrm_shutdown().

[henderkes]

Is that because the thread may not exist anymore, or is there another reason?

It's pointing to __thread memory of another thread, but the only way it got here is if a foreign thread already died, so we'd be accessing dangling memory. It's technically accessible but there's no telling what running the dtor would lead to.

We need to ensure that shutdown_memory_manager(CG(unclean_shutdown), 1); is called in php_module_shutdown. Currently we avoid calling it in ZTS builds because we rely on the TSRM dtor, I believe.

Is this a general request? I don't change the main thread shutdown path here (it gets dtor defined and is guaranteed to run its own thread). If it's just a general request, I would postpone that to a follow-up PR.

I would go as far as removing the dtor argument from ts_allocate_tls_id since it's not going to be called for most threads during tsrm_shutdown().

Can't currently do that for AG because it does pass and run the dtor.