Ignore unwinding edges when checking for unconditional recursion

[tmiasko]

The unconditional recursion lint determines if all execution paths
eventually lead to a self-recursive call.

The implementation always follows unwinding edges which limits its
practical utility. For example, it would not lint function f because a
call to g might unwind. It also wouldn't lint function h because an
overflow check preceding the self-recursive call might unwind:

pub fn f() {
    g();
    f();
}

pub fn g() { /* ... */ }

pub fn h(a: usize) {
  h(a + 1);
}

To avoid the issue, assume that terminators that might continue
execution along non-unwinding edges do so.

Fixes #78474.

[rust-highfive]

r? @estebank

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

[tmiasko]

r? @ecstatic-morse

[ecstatic-morse]

This seems strictly better while preserving existing behavior for the cases in #54444. There might be an interpretation of "lints have zero false positives" and "unconditional recursion" that would cause people to disagree with this change, but I think that interpretation is too narrow.

Thanks tmiasko!

@bors r+ rollup

[bors]

📌 Commit 10b722c has been approved by ecstatic-morse

[bors]

⌛ Testing commit 10b722c with merge 21b4a9c...

[bors]

☀️ Test successful - checks-actions
Approved by: ecstatic-morse
Pushing 21b4a9c to master...

[rust-timer]

Finished benchmarking commit (21b4a9c): comparison url.

Summary: This benchmark run shows 36 relevant regressions 😿 to instruction counts.

• Average relevant regression: 2.9%
• Largest regression in instruction counts: 14.3% on full builds of projection-caching check

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

Next Steps: If you can justify the regressions found in this perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please open an issue or create a new PR that fixes the regressions, add a comment linking to the newly created issue or PR, and then add the perf-regression-triaged label to this PR.

@rustbot label: +perf-regression

[tmiasko]

The performance regression will be addressed by changes from #93381.

@rustbot label: +perf-regression-triaged