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Describing some things that took me a long time to understand.
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Nicholas Nethercote 2024-11-18 15:43:13 +11:00
parent 0066acf753
commit 7e704afc2d
5 changed files with 24 additions and 12 deletions
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14
compiler/rustc_mir_dataflow/src/framework/cursor.rs
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@ -8,12 +8,16 @@ use rustc_middle::mir::{self, BasicBlock, Location};
use super::{Analysis, Direction, Effect, EffectIndex, Results};
/// Allows random access inspection of the results of a dataflow analysis.
/// Allows random access inspection of the results of a dataflow analysis. Use this when you want
/// to inspect domain values only in certain locations; use `ResultsVisitor` if you want to inspect
/// domain values in many or all locations.
///
/// This cursor only has linear performance within a basic block when its statements are visited in
/// the same order as the `DIRECTION` of the analysis. In the worst case—when statements are
/// visited in *reverse* order—performance will be quadratic in the number of statements in the
/// block. The order in which basic blocks are inspected has no impact on performance.
/// Because `Results` only has domain values for the entry of each basic block, these inspections
/// involve some amount of domain value recomputations. This cursor only has linear performance
/// within a basic block when its statements are visited in the same order as the `DIRECTION` of
/// the analysis. In the worst case—when statements are visited in *reverse* order—performance will
/// be quadratic in the number of statements in the block. The order in which basic blocks are
/// inspected has no impact on performance.
pub struct ResultsCursor<'mir, 'tcx, A>
where
A: Analysis<'tcx>,