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canonicalizer: add lookup table #125495

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canonicalizer: add lookup table #125495

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77 changes: 49 additions & 28 deletions compiler/rustc_next_trait_solver/src/canonicalizer.rs
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Original file line number Diff line number Diff line change
@@ -1,5 +1,6 @@
use std::cmp::Ordering;

use rustc_type_ir::data_structures::HashMap;
use rustc_type_ir::fold::{TypeFoldable, TypeFolder, TypeSuperFoldable};
use rustc_type_ir::inherent::*;
use rustc_type_ir::visit::TypeVisitableExt;
Expand Down Expand Up @@ -44,6 +45,8 @@ pub struct Canonicalizer<'a, D: SolverDelegate<Interner = I>, I: Interner> {
canonicalize_mode: CanonicalizeMode,

variables: &'a mut Vec<I::GenericArg>,
variable_lookup_table: HashMap<I::GenericArg, usize>,

primitive_var_infos: Vec<CanonicalVarInfo<I>>,
binder_index: ty::DebruijnIndex,
}
Expand All @@ -60,6 +63,7 @@ impl<'a, D: SolverDelegate<Interner = I>, I: Interner> Canonicalizer<'a, D, I> {
canonicalize_mode,

variables,
variable_lookup_table: Default::default(),
primitive_var_infos: Vec::new(),
binder_index: ty::INNERMOST,
};
Expand All @@ -75,6 +79,37 @@ impl<'a, D: SolverDelegate<Interner = I>, I: Interner> Canonicalizer<'a, D, I> {
Canonical { defining_opaque_types, max_universe, variables, value }
}

fn get_or_insert_bound_var(
&mut self,
arg: impl Into<I::GenericArg>,
canonical_var_info: CanonicalVarInfo<I>,
) -> ty::BoundVar {
// FIXME: 16 is made up and arbitrary. We should look at some
// perf data here.
let arg = arg.into();
let idx = if self.variables.len() > 16 {
if self.variable_lookup_table.is_empty() {
self.variable_lookup_table.extend(self.variables.iter().copied().zip(0..));
}

*self.variable_lookup_table.entry(arg).or_insert_with(|| {
let var = self.variables.len();
self.variables.push(arg);
self.primitive_var_infos.push(canonical_var_info);
var
})
} else {
self.variables.iter().position(|&v| v == arg).unwrap_or_else(|| {
let var = self.variables.len();
self.variables.push(arg);
self.primitive_var_infos.push(canonical_var_info);
var
})
};

ty::BoundVar::from(idx)
}

fn finalize(self) -> (ty::UniverseIndex, I::CanonicalVars) {
let mut var_infos = self.primitive_var_infos;
// See the rustc-dev-guide section about how we deal with universes
Expand Down Expand Up @@ -124,8 +159,8 @@ impl<'a, D: SolverDelegate<Interner = I>, I: Interner> Canonicalizer<'a, D, I> {
// - var_infos: [E0, U1, E2, U1, E1, E6, U6], curr_compressed_uv: 2, next_orig_uv: 6
// - var_infos: [E0, U1, E1, U1, E1, E3, U3], curr_compressed_uv: 2, next_orig_uv: -
//
// This algorithm runs in `O(n²)` where `n` is the number of different universe
// indices in the input. This should be fine as `n` is expected to be small.
// This algorithm runs in `O(mn)` where `n` is the number of different universes and
// `m` the number of variables. This should be fine as both are expected to be small.
let mut curr_compressed_uv = ty::UniverseIndex::ROOT;
let mut existential_in_new_uv = None;
let mut next_orig_uv = Some(ty::UniverseIndex::ROOT);
Expand Down Expand Up @@ -279,20 +314,20 @@ impl<D: SolverDelegate<Interner = I>, I: Interner> TypeFolder<I> for Canonicaliz
}
};

let existing_bound_var = match self.canonicalize_mode {
CanonicalizeMode::Input => None,
let var = match self.canonicalize_mode {
CanonicalizeMode::Input => {
// It's fine to not add `r` to the lookup table, as we will
// never lookup regions when canonicalizing inputs.
let var = ty::BoundVar::from(self.variables.len());
self.variables.push(r.into());
self.primitive_var_infos.push(CanonicalVarInfo { kind });
var
}
CanonicalizeMode::Response { .. } => {
self.variables.iter().position(|&v| v == r.into()).map(ty::BoundVar::from)
self.get_or_insert_bound_var(r, CanonicalVarInfo { kind })
}
};

let var = existing_bound_var.unwrap_or_else(|| {
let var = ty::BoundVar::from(self.variables.len());
self.variables.push(r.into());
self.primitive_var_infos.push(CanonicalVarInfo { kind });
var
});

Region::new_anon_bound(self.cx(), self.binder_index, var)
}

Expand Down Expand Up @@ -373,14 +408,7 @@ impl<D: SolverDelegate<Interner = I>, I: Interner> TypeFolder<I> for Canonicaliz
| ty::Error(_) => return t.super_fold_with(self),
};

let var = ty::BoundVar::from(
self.variables.iter().position(|&v| v == t.into()).unwrap_or_else(|| {
let var = self.variables.len();
self.variables.push(t.into());
self.primitive_var_infos.push(CanonicalVarInfo { kind });
var
}),
);
let var = self.get_or_insert_bound_var(t, CanonicalVarInfo { kind });

Ty::new_anon_bound(self.cx(), self.binder_index, var)
}
Expand Down Expand Up @@ -421,14 +449,7 @@ impl<D: SolverDelegate<Interner = I>, I: Interner> TypeFolder<I> for Canonicaliz
| ty::ConstKind::Expr(_) => return c.super_fold_with(self),
};

let var = ty::BoundVar::from(
self.variables.iter().position(|&v| v == c.into()).unwrap_or_else(|| {
let var = self.variables.len();
self.variables.push(c.into());
self.primitive_var_infos.push(CanonicalVarInfo { kind });
var
}),
);
let var = self.get_or_insert_bound_var(c, CanonicalVarInfo { kind });

Const::new_anon_bound(self.cx(), self.binder_index, var)
}
Expand Down
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