Move stable hasher out of rustc_middle

[cjgillot]

Continuing the effort of dismantling rustc_middle,
rustc_middle::ich and half of rustc_middle::middle are moved into a dependency crate.

The new crate name is open for bikeshedding.

[rust-highfive]

r? @estebank

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[Mark-Simulacrum]

This seems like a very disjoint set of modules -- are they all interdependent? If not, it seems odd to move them into a new crate as a single group.

[cjgillot]

I started by aiming at cstore, which is needed for ICH, and with what I could in rustc_middle::middle.
I welcome suggestions on the correct place for each module.

[Mark-Simulacrum]

We'll want to perf run this once the merge conflict is resolved.

[bors]

☔ The latest upstream changes (presumably #79070) made this pull request unmergeable. Please resolve the merge conflicts.

Note that reviewers usually do not review pull requests until merge conflicts are resolved! Once you resolve the conflicts, you should change the labels applied by bors to indicate that your PR is ready for review. Post this as a comment to change the labels:

@rustbot modify labels: +S-waiting-on-review -S-waiting-on-author

[cjgillot]

@rustbot modify labels: +S-waiting-on-review -S-waiting-on-author

[Xanewok]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion

[bors]

⌛ Trying commit 9c79f60 with merge 683d8cf848cae47f0c8ecfa2d48e9125c843e292...

[bors]

☀️ Try build successful - checks-actions
Build commit: 683d8cf848cae47f0c8ecfa2d48e9125c843e292 (683d8cf848cae47f0c8ecfa2d48e9125c843e292)

[rust-timer]

Queued 683d8cf848cae47f0c8ecfa2d48e9125c843e292 with parent f5230fb, future comparison URL.

[rust-timer]

Finished benchmarking try commit (683d8cf848cae47f0c8ecfa2d48e9125c843e292): comparison url.

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. Please note that if the perf results are neutral, you should likely undo the rollup=never given below by specifying rollup- to bors.

Importantly, though, if the results of this run are non-neutral do not roll this PR up -- it will mask other regressions or improvements in the roll up.

@bors rollup=never
@rustbot modify labels: +S-waiting-on-review -S-waiting-on-perf

[cjgillot]

perf seems neutral.

[petrochenkov]

@cjgillot
Could you explain what is the purpose of introducing rustc_crate if no dependencies on rustc_middle were removed and rustc_middle still depends on rustc_crate?
This doesn't introduce new parallelism and can only make sense if compilation time grows superlinearly with crate size.

[cjgillot]

I agree. Marking as draft until I can achieve dependency reduction.