[ruby-core:106859] [Ruby master Feature#18440] YJIT is enabled if any YJIT tuning options are set

Issue #18440 has been updated by k0kubun (Takashi Kokubun).

Backport deleted (2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN)
ruby -v deleted (ruby 3.1.0p0 (2021-12-25 revision fb4df44d16) [arm64-darwin21])
Tracker changed from Bug to Feature

> From the code, this appears to be intentional. 

I think so. At least for MJIT in 2.6~3.0, we used to show:

```
  --jit           enable JIT with default options (experimental)
  --jit-[option]  enable JIT with an option (experimental)
```

but we ended up removing it in 3.1 for MJIT and YJIT. Maybe we should add such descriptions again for clarity.

----------------------------------------
Feature #18440: YJIT is enabled if any YJIT tuning options are set
https://bugs.ruby-lang.org/issues/18440#change-95670

* Author: georgeclaghorn (George Claghorn)
* Status: Open
* Priority: Normal
----------------------------------------
I was testing YJIT in a Rails app with `RUBYOPT="--yjit --yjit-exec-mem-size=32"`. I saw some weird issues around Rails view caching, so I attempted to temporarily disable YJIT by removing `--yjit` and leaving the tuning options in place (`RUBYOPT="--yjit-exec-mem-size=32"`). However, YJIT remained enabled until I also removed `--yjit-exec-mem-size=32`.

```
$ ruby -e 'puts RubyVM::YJIT.runtime_stats.inspect'
nil

$ ruby --yjit-exec-mem-size -e 'puts RubyVM::YJIT.runtime_stats.inspect'
{:inline_code_size=>378495, :outlined_code_size=>311079}
```

I expected removing `--yjit` to disable YJIT and was surprised by this.



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