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Check for trivial cycles in persue_answer #469

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May 22, 2020
Merged

Check for trivial cycles in persue_answer #469

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Check for trivial cycles in persue_answer
zaharidichev May 22, 2020
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zaharidichev May 22, 2020
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34 changes: 16 additions & 18 deletions chalk-engine/src/logic.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -909,14 +909,9 @@ impl<'forest, C: Context + 'forest, CO: ContextOps<C> + 'forest> SolveState<'for
// we might have to build on it (see the
// Delayed Trivial Self Cycle, Variant 3
// example).
let (_, _, _, table_goal) = self
.context
.instantiate_ucanonical_goal(&self.forest.tables[table].table_goal);

let answer = self.forest.answer(table, answer_index);
if let Some(strand) =
self.create_refinement_strand(table, answer, table_goal)
{
if let Some(strand) = self.create_refinement_strand(table, answer) {
self.forest.tables[table].enqueue_strand(strand);
}

Expand Down Expand Up @@ -964,7 +959,6 @@ impl<'forest, C: Context + 'forest, CO: ContextOps<C> + 'forest> SolveState<'for
&self,
table: TableIndex,
answer: &Answer<C>,
table_goal: C::Goal,
) -> Option<CanonicalStrand<C>> {
// If there are no delayed subgoals, then there is no need for
// a refinement strand.
Expand All @@ -977,16 +971,8 @@ impl<'forest, C: Context + 'forest, CO: ContextOps<C> + 'forest> SolveState<'for
.context
.instantiate_answer_subst(num_universes, &answer.subst);

// FIXME: it would be nice if these delayed subgoals didn't get added to the answer
// at all. However, we can't compare the delayed subgoals with the table goal until
// we call `canonicalize_answer_subst` in `pursue_answer`. However, at this point,
// it's a bit late since `pursue_answer` doesn't know about the table goal. This could
// be refactored a bit.
let filtered_delayed_subgoals = delayed_subgoals
let delayed_subgoals = delayed_subgoals
.into_iter()
.filter(|delayed_subgoal| {
*C::goal_from_goal_in_environment(delayed_subgoal) != table_goal
})
.map(Literal::Positive)
.collect();

Expand All @@ -996,7 +982,7 @@ impl<'forest, C: Context + 'forest, CO: ContextOps<C> + 'forest> SolveState<'for
subst,
ambiguous: answer.ambiguous,
constraints,
subgoals: filtered_delayed_subgoals,
subgoals: delayed_subgoals,
delayed_subgoals: Vec::new(),
answer_time: TimeStamp::default(),
floundered_subgoals: Vec::new(),
Expand Down Expand Up @@ -1328,11 +1314,23 @@ impl<'forest, C: Context + 'forest, CO: ContextOps<C> + 'forest> SolveState<'for
return None;
}

let table = self.stack.top().table;
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This is already in scope at the beginning of the function.

let table_goal = &self.forest.tables[table].table_goal;

let filtered_delayed_subgoals = delayed_subgoals
.into_iter()
.filter(|delayed_subgoal| {
let (canonicalized, _) =
infer.fully_canonicalize_goal(self.context.interner(), delayed_subgoal);
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*table_goal != canonicalized
})
.collect();

let subst = infer.canonicalize_answer_subst(
self.context.interner(),
subst,
constraints,
delayed_subgoals,
filtered_delayed_subgoals,
);
debug!("answer: table={:?}, subst={:?}", table, subst);

Expand Down
19 changes: 3 additions & 16 deletions chalk-solve/src/solve/slg/resolvent.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -236,10 +236,6 @@ impl<I: Interner> context::ResolventOps<SlgContext<I>> for TruncatingInferenceTa
.infer
.instantiate_canonical(interner, &canonical_answer_subst);

let table_goal = self
.infer
.instantiate_canonical(interner, &answer_table_goal);

AnswerSubstitutor::substitute(
interner,
&mut self.infer,
Expand All @@ -250,18 +246,9 @@ impl<I: Interner> context::ResolventOps<SlgContext<I>> for TruncatingInferenceTa
selected_goal,
)?;
ex_clause.constraints.extend(answer_constraints);

for delayed_subgoal in delayed_subgoals {
// FIXME: is this always valid or would we ever run
// into an issue with normalization? (Would this even
// be a "trivial self-cycle"?)
// Only add the delayed_subgoals to the ex-clause if
// it isn't a trivial self-cycle
if delayed_subgoal.goal != table_goal.goal {
ex_clause.delayed_subgoals.push(delayed_subgoal);
}
}

// at that point we should only have goals that stemmed
// from non trivial self cycles
ex_clause.delayed_subgoals.extend(delayed_subgoals);
Ok(())
}
}
Expand Down