Always fall back to PartialEq when a constant in a pattern is not recursively structural-eq

[oli-obk]

Right now we destructure the constant as far as we can, but with this PR we just don't take it apart anymore. This is preparatory work for moving to always using valtrees, as these will just do a single conversion of the constant to a valtree at the start, and if that fails, fall back to PartialEq.

This removes a few cases where we emitted the unreachable pattern lint, because we stop looking into the constant deeply enough to detect that a constant is already covered by another pattern.

Previous work: #70743

This is groundwork towards fixing #83085 and #105047

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @petrochenkov (or someone else) soon.

Please see the contribution instructions for more information.

[oli-obk]

I can add the rest of the valtree work to this PR if preferred, but I thought I'd submit it in this small form first.

[pnkfelix]

@bors try @rust-timer queue

[bors]

⌛ Trying commit ed0627422a3a653595718616513ce5b8a8aab8c6 with merge 73bd817a44e4fa3751ed828e99297caf55470e77...

[bors]

☀️ Try build successful - checks-actions
Build commit: 73bd817a44e4fa3751ed828e99297caf55470e77 (73bd817a44e4fa3751ed828e99297caf55470e77)

[rust-timer]

Finished benchmarking commit (73bd817a44e4fa3751ed828e99297caf55470e77): comparison URL.

Overall result: no relevant changes - no action needed

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 may lead to changes in compiler perf.

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

Instruction count

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Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.3%	[-2.3%, -2.3%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.3%	[-2.3%, -2.3%]	1

Cycles

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[oli-obk]

Blocked on making all function pointers PartialEq, even ones with higher ranked lifetimes,

[RalfJung]

Blocked on making all function pointers PartialEq, even ones with higher ranked lifetimes,

So, basically #99531. It's not impossible but it seems hard.

---

If I understand correctly, this PR still uses the old "destructure const" machinery to build the pattern tree. Is the idea that after this PR, we can change that to use valtrees (and remove const destructuring) without further behavior changes?

[oli-obk]

Is the idea that after this PR, we can change that to use valtrees (and remove const destructuring) without further behavior changes?

Yes, I have tried this locally and it works and will permit more cleanups

[apiraino]

Hello, checking status for this PR. Thanks for an update! cc @oli-obk @RalfJung

[oli-obk]

Still blocked on #99531

[oli-obk]

@rustbot author

we got a FnPtr trait now that implements PartialEq for all function pointers

[oli-obk]

@bors r-

[oli-obk]

@bors r=lcnr

[bors]

📌 Commit 2282258 has been approved by lcnr

It is now in the queue for this repository.

[bors]

⌛ Testing commit 2282258 with merge 9239760...

[bors]

☀️ Test successful - checks-actions
Approved by: lcnr
Pushing 9239760 to master...

[rust-timer]

Finished benchmarking commit (9239760): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

This benchmark run did not return any relevant results for this metric.

Cycles

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Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 641.949s -> 642.522s (0.09%)