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Merged
bors merged 1 commit into from
Nov 9, 2018
+4 −4
Merged

Improve creation of 3 IndexVecs #55755

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3 changes: 1 addition & 2 deletions src/librustc/ty/query/on_disk_cache.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -450,8 +450,7 @@ impl<'sess> OnDiskCache<'sess> {
.map(|&(cnum, ..)| cnum)
.max()
.unwrap_or(0) + 1;
let mut map = IndexVec::new();
map.resize(map_size as usize, None);
let mut map = IndexVec::from_elem_n(None, map_size as usize);

for &(prev_cnum, ref crate_name, crate_disambiguator) in prev_cnums {
let key = (crate_name.clone(), crate_disambiguator);
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5 changes: 3 additions & 2 deletions src/librustc_mir/shim.rs
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Expand Up @@ -196,7 +196,7 @@ fn build_drop_shim<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
let source_info = SourceInfo { span, scope: OUTERMOST_SOURCE_SCOPE };

let return_block = BasicBlock::new(1);
let mut blocks = IndexVec::new();
let mut blocks = IndexVec::with_capacity(2);
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@pnkfelix pnkfelix Nov 8, 2018

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hmm do we want/need a SmallIndexVec that is analogous to SmallVec ...?

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@pnkfelix pnkfelix Nov 8, 2018

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or ... should we try something bonkers like changing IndexVec to use a SmallVec internally...?

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@ljedrz ljedrz Nov 8, 2018

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I could submit an experimental PR to check the perf implications.

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@ljedrz ljedrz Nov 8, 2018

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This is harder than I thought; changing the underlying structure of IndexVec to a SmallVec makes Mir a recursive type of infinite size due to the promoted component.

let block = |blocks: &mut IndexVec<_, _>, kind| {
blocks.push(BasicBlockData {
statements: vec![],
Expand Down Expand Up @@ -768,7 +768,8 @@ fn build_call_shim<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
}));
}

let mut blocks = IndexVec::new();
let n_blocks = if let Adjustment::RefMut = rcvr_adjustment { 5 } else { 2 };
let mut blocks = IndexVec::with_capacity(n_blocks);
let block = |blocks: &mut IndexVec<_, _>, statements, kind, is_cleanup| {
blocks.push(BasicBlockData {
statements,
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