Struct mz_transform::cse::relation_cse::Bindings

pub struct Bindings {
    bindings: BTreeMap<MirRelationExpr, u64>,
    rebindings: BTreeMap<LocalId, LocalId>,
    recursion_guard: RecursionGuard,
}

Maintains Let bindings in a compact, explicit representation.

The bindings map contains neither Let bindings nor two structurally equivalent expressions.

The bindings can be interpreted as an ordered sequence of let bindings, ordered by their identifier, that should be applied in order before the use of the expression from which they have been extracted.

Fields

bindings: BTreeMap<MirRelationExpr, u64>

A list of let-bound expressions and their order / identifier.

rebindings: BTreeMap<LocalId, LocalId>

Mapping from conventional local Get identifiers to new ones.

recursion_guard: RecursionGuard

Implementations

impl Bindings

fn intern_expression( &mut self, relation: &mut MirRelationExpr ) -> Result<(), TransformError>

Replace relation with an equivalent Get expression referencing a location in bindings.

The algorithm performs a post-order traversal of the expression tree, binding each distinct expression to a new local identifier. It maintains the invariant that bindings contains no Let expressions, nor any two structurally equivalent expressions.

Once each sub-expression is replaced by a canonical Get expression, each expression is also in a canonical representation, which is used to check for prior instances and drives re-use.

fn populate_expression(self, expression: &mut MirRelationExpr)

Populates expression with necessary Let bindings.

This population may result in substantially more Let bindings that one might expect. It is very appropriate to run the NormalizeLets transformation afterwards to remove Let bindings that it deems unhelpful.

Trait Implementations

impl CheckedRecursion for Bindings

fn recursion_guard(&self) -> &RecursionGuard

Extracts a reference to the recursion guard embedded within the type.

fn checked_recur<F, T, E>(&self, f: F) -> Result<T, E>where F: FnOnce(&Self) -> Result<T, E>, E: From<RecursionLimitError>,

Checks whether it is safe to recur and calls f if so.

fn checked_recur_mut<F, T, E>(&mut self, f: F) -> Result<T, E>where F: FnOnce(&mut Self) -> Result<T, E>, E: From<RecursionLimitError>,

Like CheckedRecursion::checked_recur, but operates on a mutable reference to Self.

impl Debug for Bindings

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Bindings

fn default() -> Bindings

Returns the “default value” for a type.