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Rollup merge of #137216 - amandasystems:cheap-outlives-eval, r=compiler-errors

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eval_outlives: bail out early if both regions are in the same SCC

A drive-by optimisation of region outlives evaluation: if we are evaluating whether an outlives holds for two regions, bail out early if they are both in the same SCC.

This probably won't make a huge difference, but the cost is one comparison of SCC indices (integers).

May want a perf run, depending on how confident whomever reviewing this is!
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Matthias Krüger 2025-02-19 01:30:13 +01:00 • committed by GitHub
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5
compiler/rustc_borrowck/src/region_infer/mod.rs
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@ -1267,6 +1267,11 @@ impl<'tcx> RegionInferenceContext<'tcx> {
let sub_region_scc = self.constraint_sccs.scc(sub_region); let sub_region_scc = self.constraint_sccs.scc(sub_region);
let sup_region_scc = self.constraint_sccs.scc(sup_region); let sup_region_scc = self.constraint_sccs.scc(sup_region);
if sub_region_scc == sup_region_scc {
debug!("{sup_region:?}: {sub_region:?} holds trivially; they are in the same SCC");
return true;
}
// If we are checking that `'sup: 'sub`, and `'sub` contains // If we are checking that `'sup: 'sub`, and `'sub` contains
// some placeholder that `'sup` cannot name, then this is only // some placeholder that `'sup` cannot name, then this is only
// true if `'sup` outlives static. // true if `'sup` outlives static.