Refactor query system to maintain a global job id counter

[Mark-Simulacrum]

This replaces the per-shard counters with a single global counter, simplifying
the JobId struct down to just a u64 and removing the need to pipe a DepKind
generic through a bunch of code. The performance implications on non-parallel
compilers are likely minimal (this switches to Cell<u64> as the backing
storage over a u64, but the latter was already inside a RefCell so it's not
really a significance divergence). On parallel compilers, the cost of a single
global u64 counter may be more significant: it adds a serialization point in
theory. On the other hand, we can imagine changing the counter to have a
thread-local component if it becomes worrisome or some similar structure.

The new design is sufficiently simpler that it warrants the potential for slight
changes down the line if/when we get parallel compilation to be more of a
default.

A u64 counter, instead of u32 (the old per-shard width), is chosen to avoid
possibly overflowing it and causing problems; it is effectively impossible that
we would overflow a u64 counter in this context.

[rust-highfive]

r? @oli-obk

(rust-highfive has picked a reviewer for you, use r? to override)

[Mark-Simulacrum]

@bors try @rust-timer queue

Expecting this to potentially cause some noise just because this code is quite hot, but likely to be largely neutral.

[rust-timer]

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

[bors]

⌛ Trying commit d4a783abdfc9cad833f87532e231523117194764 with merge 5ebf14f5a1b120efc229c7b3b2e2571d82dc7496...

[bors]

☀️ Try build successful - checks-actions
Build commit: 5ebf14f5a1b120efc229c7b3b2e2571d82dc7496 (5ebf14f5a1b120efc229c7b3b2e2571d82dc7496)

[rust-timer]

Queued 5ebf14f5a1b120efc229c7b3b2e2571d82dc7496 with parent c5e4148, future comparison URL.

[rust-timer]

Finished benchmarking commit (5ebf14f5a1b120efc229c7b3b2e2571d82dc7496): comparison url.

Summary: This benchmark run shows 3 relevant regressions 😿 to instruction counts.

• Average relevant regression: 1.2%
• Largest regression in instruction counts: 1.2% on incr-unchanged builds of ctfe-stress-4 check

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR led to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

@bors rollup=never
@rustbot label: +S-waiting-on-review -S-waiting-on-perf +perf-regression

[Mark-Simulacrum]

Similar to #93724 (comment), the regression seems real but is likely optimizer noise we can't really do much about.

[cjgillot]

For the moment, the parallel compiler efforts have pretty much stalled.
This is a great simplification, which should not irreversibly break the parallel compiler.
@bors r+

[bors]

📌 Commit d4a783abdfc9cad833f87532e231523117194764 has been approved by cjgillot

[Mark-Simulacrum]

@bors r-

I was thinking about this and realized we should keep the checked_add to ensure uniqueness, so will just amend this and r=you with that most likely.

[Mark-Simulacrum]

@bors r=cjgillot

Replaced the u32 with a u64 -- even simpler, and avoids complicated increments to the atomic in a parallel context.

[bors]

📌 Commit e240783 has been approved by cjgillot

[bors]

⌛ Testing commit e240783 with merge e7aca89...

[bors]

☀️ Test successful - checks-actions
Approved by: cjgillot
Pushing e7aca89 to master...

[rust-timer]

Finished benchmarking commit (e7aca89): comparison url.

Summary: This benchmark run did not return any relevant results. 28 results were found to be statistically significant but too small to be relevant.

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

@rustbot label: -perf-regression