pattern_analysis: track usefulness without interior mutability

[Nadrieril]

Because of or-patterns, exhaustiveness needs to be able to lint if a sub-pattern is redundant, e.g. in Some(_) | Some(true). So far the only sane solution I had found was interior mutability. This is a bit of an abstraction leak, and would become a footgun if we ever reused the same DeconstructedPat. This PR replaces interior mutability with an address-indexed hashmap, which is logically equivalent.

[rustbot]

r? @cjgillot

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[Nadrieril]

r? @ghost

[rustbot]

Failed to set assignee to ghost: invalid assignee

Note: Only org members with at least the repository "read" role, users with write permissions, or people who have commented on the PR may be assigned.

[Nadrieril]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 8f04a1e with merge 09d4a12...

[bors]

☀️ Try build successful - checks-actions
Build commit: 09d4a12 (09d4a121c582c90b8bff6f6018482f56ef291895)

[rust-timer]

Finished benchmarking commit (09d4a12): 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

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

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)	4.2%	[4.2%, 4.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.7%	[-2.8%, -2.7%]	2
All ❌✅ (primary)	-	-	0

Cycles

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

Binary size

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

Bootstrap: 664.789s -> 665.467s (0.10%)
Artifact size: 308.40 MiB -> 308.41 MiB (0.00%)

[Nadrieril]

r? @compiler-errors
@rustbot ready

[compiler-errors]

Hmm... I have mixed feelings about using address-based indexing here :|

Is there any way we could give some other kind of unique ID to all the DeconstructedPats for use in tracking this state instead?

[Nadrieril]

We could store a AtomicUsize-generated id in DeconstructedPat, like I do for Constructor::Opaque. Using the spans is tempting but fails in the presence of macros. Would you prefer that?

[compiler-errors]

Yeah, spans are a no-go. They're not unique. I would prefer a real dedicated ID. Why does it need to be atomic? We don't expect it to be modified after the DeconstructedPat is created, right?

[Nadrieril]

Oh indeed, I meant storing a usize, but made globally unique by incrementing a static AtomicUsize

[Nadrieril]

@rustbot ready

[compiler-errors]

@bors r+

[bors]

📌 Commit be29cd1 has been approved by compiler-errors

It is now in the queue for this repository.

[bors]

⌛ Testing commit be29cd1 with merge 74c3f5a...

[bors]

☀️ Test successful - checks-actions
Approved by: compiler-errors
Pushing 74c3f5a to master...

[rust-timer]

Finished benchmarking commit (74c3f5a): 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

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

Binary size

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

Bootstrap: 664.301s -> 664.029s (-0.04%)
Artifact size: 308.35 MiB -> 308.34 MiB (-0.01%)