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rustc: Sort CGUs before merging #46918

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Merged
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Dec 22, 2017
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rustc: Sort CGUs before merging #46918

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11 changes: 11 additions & 0 deletions src/librustc_mir/monomorphize/partitioning.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -377,6 +377,17 @@ fn merge_codegen_units<'tcx>(initial_partitioning: &mut PreInliningPartitioning<
assert!(target_cgu_count >= 1);
let codegen_units = &mut initial_partitioning.codegen_units;

// Note that at this point in time the `codegen_units` here may not be in a
// deterministic order (but we know they're deterministically the same set).
// We want this merging to produce a deterministic ordering of codegen units
// from the input.
//
// Due to basically how we've implemented the merging below (merge the two
// smallest into each other) we're sure to start off with a deterministic
// order (sorted by name). This'll mean that if two cgus have the same size
// the stable sort below will keep everything nice and deterministic.
codegen_units.sort_by_key(|cgu| cgu.name().clone());

// Merge the two smallest codegen units until the target size is reached.
// Note that "size" is estimated here rather inaccurately as the number of
// translation items in a given unit. This could be improved on.
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