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Add documentation to the Analysis traits

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This commit is contained in:
Dylan MacKenzie 2020-08-30 14:18:49 -07:00
parent e178a87036
commit b015109ba9
1 changed files with 19 additions and 3 deletions
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22
compiler/rustc_mir/src/dataflow/framework/mod.rs
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@ -60,9 +60,10 @@ pub use self::visitor::{BorrowckFlowState, BorrowckResults};
/// This trait specifies the lattice on which this analysis operates (the domain) as well as its
/// initial value at the entry point of each basic block.
pub trait AnalysisDomain<'tcx> {
/// The type that holds the dataflow state at any given point in the program.
type Domain: Clone + JoinSemiLattice;
/// The direction of this analyis. Either `Forward` or `Backward`.
/// The direction of this analysis. Either `Forward` or `Backward`.
type Direction: Direction = Forward;
/// A descriptive name for this analysis. Used only for debugging.
@ -71,10 +72,10 @@ pub trait AnalysisDomain<'tcx> {
/// suitable as part of a filename.
const NAME: &'static str;
/// The initial value of the dataflow state upon entry to each basic block.
fn bottom_value(&self, body: &mir::Body<'tcx>) -> Self::Domain;
/// Mutates the entry set of the `START_BLOCK` to contain the initial state for dataflow
/// analysis.
/// Mutates the initial value of the dataflow state upon entry to the `START_BLOCK`.
///
/// For backward analyses, initial state besides the bottom value is not yet supported. Trying
/// to mutate the initial state will result in a panic.
@ -86,6 +87,21 @@ pub trait AnalysisDomain<'tcx> {
}
/// A dataflow problem with an arbitrarily complex transfer function.
///
/// # Convergence
///
/// When implementing this trait directly (not via [`GenKillAnalysis`]), it's possible to choose a
/// transfer function such that the analysis does not reach fixpoint. To guarantee convergence,
/// your transfer functions must maintain the following invariant:
///
/// > If the dataflow state **before** some point in the program changes to be greater
/// than the prior state **before** that point, the dataflow state **after** that point must
/// also change to be greater than the prior state **after** that point.
///
/// This invariant guarantees that the dataflow state at a given point in the program increases
/// monotonically until fixpoint is reached. Note that this monotonicity requirement only applies
/// to the same point in the program at different points in time. The dataflow state at a given
/// point in the program may or may not be greater than the state at any preceding point.
pub trait Analysis<'tcx>: AnalysisDomain<'tcx> {
/// Updates the current dataflow state with the effect of evaluating a statement.
fn apply_statement_effect(