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auto merge of #14563 : dotdash/rust/clone_kill, r=huonw
By dropping the intermediate vector that holds the relevant candidates including duplicates and directly building the vector that has the duplicates removed we can eliminate quite a few allocations. This reduces the times for type checking by 5-10% (measured with libstd, libsyntax and librustc).
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src/librustc/middle/typeck/check/method.rs

Lines changed: 10 additions & 34 deletions
Original file line numberDiff line numberDiff line change
@@ -1026,13 +1026,7 @@ impl<'a> LookupContext<'a> {
10261026
fn consider_candidates(&self, rcvr_ty: ty::t,
10271027
candidates: &[Candidate])
10281028
-> Option<MethodCallee> {
1029-
// FIXME(pcwalton): Do we need to clone here?
1030-
let relevant_candidates: Vec<Candidate> =
1031-
candidates.iter().map(|c| (*c).clone()).
1032-
filter(|c| self.is_relevant(rcvr_ty, c)).collect();
1033-
1034-
let relevant_candidates =
1035-
self.merge_candidates(relevant_candidates.as_slice());
1029+
let relevant_candidates = self.filter_candidates(rcvr_ty, candidates);
10361030

10371031
if relevant_candidates.len() == 0 {
10381032
return None;
@@ -1069,22 +1063,16 @@ impl<'a> LookupContext<'a> {
10691063
Some(self.confirm_candidate(rcvr_ty, relevant_candidates.get(0)))
10701064
}
10711065

1072-
fn merge_candidates(&self, candidates: &[Candidate]) -> Vec<Candidate> {
1073-
let mut merged = Vec::new();
1074-
let mut i = 0;
1075-
while i < candidates.len() {
1076-
let candidate_a = &candidates[i];
1077-
1078-
let mut skip = false;
1066+
fn filter_candidates(&self, rcvr_ty: ty::t, candidates: &[Candidate]) -> Vec<Candidate> {
1067+
let mut relevant_candidates: Vec<Candidate> = Vec::new();
10791068

1080-
let mut j = i + 1;
1081-
while j < candidates.len() {
1082-
let candidate_b = &candidates[j];
1069+
for candidate_a in candidates.iter().filter(|&c| self.is_relevant(rcvr_ty, c)) {
1070+
// Skip this one if we already have one like it
1071+
if !relevant_candidates.iter().any(|candidate_b| {
10831072
debug!("attempting to merge {} and {}",
10841073
candidate_a.repr(self.tcx()),
10851074
candidate_b.repr(self.tcx()));
1086-
let candidates_same = match (&candidate_a.origin,
1087-
&candidate_b.origin) {
1075+
match (&candidate_a.origin, &candidate_b.origin) {
10881076
(&MethodParam(ref p1), &MethodParam(ref p2)) => {
10891077
let same_trait = p1.trait_id == p2.trait_id;
10901078
let same_method = p1.method_num == p2.method_num;
@@ -1095,25 +1083,13 @@ impl<'a> LookupContext<'a> {
10951083
same_trait && same_method && same_param
10961084
}
10971085
_ => false
1098-
};
1099-
if candidates_same {
1100-
skip = true;
1101-
break;
11021086
}
1103-
j += 1;
1104-
}
1105-
1106-
i += 1;
1107-
1108-
if skip {
1109-
// There are more than one of these and we need only one
1110-
continue;
1111-
} else {
1112-
merged.push(candidate_a.clone());
1087+
}) {
1088+
relevant_candidates.push(candidate_a.clone());
11131089
}
11141090
}
11151091

1116-
return merged;
1092+
relevant_candidates
11171093
}
11181094

11191095
fn confirm_candidate(&self, rcvr_ty: ty::t, candidate: &Candidate)

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