Use forward traversal for unconditional recursion lint #70973
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Neat, that does look simpler! @bors r+ |
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📌 Commit 0fc0f34 has been approved by |
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Rollup of 9 pull requests Successful merges: - rust-lang#69745 (Use `PredicateObligation`s instead of `Predicate`s) - rust-lang#70938 (Add ThreadSanitizer test case) - rust-lang#70973 (Use forward traversal for unconditional recursion lint) - rust-lang#70978 (compiletest: let config flags overwrite -A unused) - rust-lang#70979 (Follow up on BTreeMap comments) - rust-lang#70981 (Rearrange BTreeMap::into_iter to match range_mut.) - rust-lang#70985 (Clean up E0512 explanation) - rust-lang#70988 (Setup the `@rustbot prioritize` command) - rust-lang#70991 (fix rustc-dev-guide's url in src/librustc_codegen_ssa) Failed merges: r? @ghost
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While reviewing #70822, I noted that #54444 could be solved without requiring the predecessor graph and without allocating a
Vec<Span>for every basic block. The unconditional recursion lint is not a performance bottleneck however, so I approved #70822 as it was.Nevertheless, I wanted to try implementing my idea using
TriColorDepthFirstSearch, which is a DFS that can differentiate between forward/tree edges and backward ones. I found this approach more straightforward than the existing one, so I'm opening this PR to see if it is desirable.The pass is now just a DFS across the control-flow graph. We ignore false edges and false unwinds, as well as the successors of recursive calls, just like existing pass does. If we see a back-edge (loop) or a terminator that would cause us to yield control-flow back to the caller (
Return,Resume, etc.), we know that the function does not unconditionally recurse.r? @jonas-schievink