Test performance impact of removing untracked vtable cache from tcx

[michaelwoerister]

See #89598 for more information

[rust-highfive]

r? @oli-obk

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[michaelwoerister]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

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

[bors]

⌛ Trying commit 553a808 with merge 73d3bab7d9a52285b2738553971a9ab6f4a6cf11...

[bors]

☀️ Try build successful - checks-actions
Build commit: 73d3bab7d9a52285b2738553971a9ab6f4a6cf11 (73d3bab7d9a52285b2738553971a9ab6f4a6cf11)

[rust-timer]

Queued 73d3bab7d9a52285b2738553971a9ab6f4a6cf11 with parent d7539a6, future comparison URL.

[rust-timer]

Finished benchmarking commit (73d3bab7d9a52285b2738553971a9ab6f4a6cf11): comparison url.

Summary: This change led to moderate relevant regressions 😿 in compiler performance.

• Moderate regression in instruction counts (up to 1.9% on full builds of ctfe-stress-4)

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

[oli-obk]

This is probably due to https://github.com/rust-lang/rustc-perf/blob/c7680837bb2b0a781ec2d7f1025b155ac64c0bc5/collector/benchmarks/ctfe-stress-4/src/lib.rs#L67 generating the same vtable a couple thousand times.

It's fine to regress this stress test in this way

[michaelwoerister]

Alright, good to know we might have a simple fix if we can't do a proper one in time.