From 94c5d38f0b5c85e2171dfe7b9ec36954d17f5fe0 Mon Sep 17 00:00:00 2001 From: Nicholas Nethercote Date: Tue, 1 May 2018 10:01:02 +1000 Subject: [PATCH] Use two vectors in nearest_common_ancestor. When looking at any scope in scope chain A, we only need to look for matches among scopes previously seen in scope chain B, and vice versa. This halves the number of "seen before?" comparisons, speeding up some runs of style-servo, clap-rs, and syn by 1--2%. --- src/librustc/middle/region.rs | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/src/librustc/middle/region.rs b/src/librustc/middle/region.rs index 5f4efbeeaa876..bfc9ff6660de9 100644 --- a/src/librustc/middle/region.rs +++ b/src/librustc/middle/region.rs @@ -690,21 +690,22 @@ impl<'tcx> ScopeTree { // the start. So this algorithm is faster. let mut ma = Some(scope_a); let mut mb = Some(scope_b); - let mut seen: SmallVec<[Scope; 32]> = SmallVec::new(); + let mut seen_a: SmallVec<[Scope; 32]> = SmallVec::new(); + let mut seen_b: SmallVec<[Scope; 32]> = SmallVec::new(); loop { if let Some(a) = ma { - if seen.iter().position(|s| *s == a).is_some() { + if seen_b.iter().position(|s| *s == a).is_some() { return a; } - seen.push(a); + seen_a.push(a); ma = self.parent_map.get(&a).map(|s| *s); } if let Some(b) = mb { - if seen.iter().position(|s| *s == b).is_some() { + if seen_a.iter().position(|s| *s == b).is_some() { return b; } - seen.push(b); + seen_b.push(b); mb = self.parent_map.get(&b).map(|s| *s); }