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[feedback] per-edge dataflow #47664

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[feedback] per-edge dataflow #47664

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68b9f0b
use `'_` to make clear that `BlockSets` contain references
nikomatsakis Dec 20, 2017
3f768fd
document that `sets.on_entry` is not *always* block entry
nikomatsakis Dec 20, 2017
af62153
convert `propagate_call_return` to take `sets` and be pure function
nikomatsakis Dec 20, 2017
3056861
s/&mut sets.on_entry/&sets.on_entry/
nikomatsakis Dec 20, 2017
7619704
introduce (unused) scratch buffer
nikomatsakis Dec 31, 2017
0285472
introduce helper for propagating bits across a list of edges
nikomatsakis Dec 31, 2017
5fe40f6
generalize `propagate_call_return` to `edge_effect`
nikomatsakis Dec 31, 2017
642815f
micro-optimize "anything changed?" check
nikomatsakis Dec 31, 2017
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9 changes: 4 additions & 5 deletions src/librustc_mir/dataflow/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -612,11 +612,10 @@ pub trait BitDenotation: BitwiseOperator {
/// `sets.on_entry` to that local clone into `statement_effect` and
/// `terminator_effect`).
///
/// When its false, no local clone is constucted; instead a
/// reference directly into `on_entry` is passed along via
/// `sets.on_entry` instead, which represents the flow state at
/// the block's start, not necessarily the state immediately prior
/// to the statement/terminator under analysis.
/// When its false, no local clone is constucted; instead it is
/// undefined what `on_entry` points to (in practice, it will
/// frequently be a reference the flow state at the block's start,
/// but you should not rely on that).
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I think this is a good change (in that no one should be or have been using the stronger guarantee in the earlier version of the comment). But I am curious: Did you actually concoct some scenario that invalidated the comment's stronger claim? Or are you figuring that we're better off not defining the semantics in this case?

///
/// In either case, the passed reference is mutable; but this is a
/// wart from using the `BlockSets` type in the API; the intention
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