94 lines
3.4 KiB
Rust
94 lines
3.4 KiB
Rust
use rustc_infer::infer::canonical::Canonical;
|
|
use rustc_infer::traits::query::NoSolution;
|
|
use rustc_middle::traits::solve::{Certainty, QueryResult};
|
|
use rustc_middle::ty::TyCtxt;
|
|
use rustc_session::Limit;
|
|
|
|
use super::SearchGraph;
|
|
use crate::solve::response_no_constraints_raw;
|
|
|
|
/// When detecting a solver overflow, we return ambiguity. Overflow can be
|
|
/// *hidden* by either a fatal error in an **AND** or a trivial success in an **OR**.
|
|
///
|
|
/// This is in issue in case of exponential blowup, e.g. if each goal on the stack
|
|
/// has multiple nested (overflowing) candidates. To deal with this, we reduce the limit
|
|
/// used by the solver when hitting the default limit for the first time.
|
|
///
|
|
/// FIXME: Get tests where always using the `default_limit` results in a hang and refer
|
|
/// to them here. We can also improve the overflow strategy if necessary.
|
|
pub(super) struct OverflowData {
|
|
default_limit: Limit,
|
|
current_limit: Limit,
|
|
/// When proving an **AND** we have to repeatedly iterate over the yet unproven goals.
|
|
///
|
|
/// Because of this each iteration also increases the depth in addition to the stack
|
|
/// depth.
|
|
additional_depth: usize,
|
|
}
|
|
|
|
impl OverflowData {
|
|
pub(super) fn new(tcx: TyCtxt<'_>) -> OverflowData {
|
|
let default_limit = tcx.recursion_limit();
|
|
OverflowData { default_limit, current_limit: default_limit, additional_depth: 0 }
|
|
}
|
|
|
|
#[inline]
|
|
pub(super) fn did_overflow(&self) -> bool {
|
|
self.default_limit.0 != self.current_limit.0
|
|
}
|
|
|
|
#[inline]
|
|
pub(super) fn has_overflow(&self, depth: usize) -> bool {
|
|
!self.current_limit.value_within_limit(depth + self.additional_depth)
|
|
}
|
|
|
|
/// Updating the current limit when hitting overflow.
|
|
fn deal_with_overflow(&mut self) {
|
|
// When first hitting overflow we reduce the overflow limit
|
|
// for all future goals to prevent hangs if there's an exponential
|
|
// blowup.
|
|
self.current_limit.0 = self.default_limit.0 / 8;
|
|
}
|
|
}
|
|
|
|
pub(in crate::solve) trait OverflowHandler<'tcx> {
|
|
fn search_graph(&mut self) -> &mut SearchGraph<'tcx>;
|
|
|
|
fn repeat_while_none<T>(
|
|
&mut self,
|
|
on_overflow: impl FnOnce(&mut Self) -> Result<T, NoSolution>,
|
|
mut loop_body: impl FnMut(&mut Self) -> Option<Result<T, NoSolution>>,
|
|
) -> Result<T, NoSolution> {
|
|
let start_depth = self.search_graph().overflow_data.additional_depth;
|
|
let depth = self.search_graph().stack.len();
|
|
while !self.search_graph().overflow_data.has_overflow(depth) {
|
|
if let Some(result) = loop_body(self) {
|
|
self.search_graph().overflow_data.additional_depth = start_depth;
|
|
return result;
|
|
}
|
|
|
|
self.search_graph().overflow_data.additional_depth += 1;
|
|
}
|
|
self.search_graph().overflow_data.additional_depth = start_depth;
|
|
self.search_graph().overflow_data.deal_with_overflow();
|
|
on_overflow(self)
|
|
}
|
|
}
|
|
|
|
impl<'tcx> OverflowHandler<'tcx> for SearchGraph<'tcx> {
|
|
fn search_graph(&mut self) -> &mut SearchGraph<'tcx> {
|
|
self
|
|
}
|
|
}
|
|
|
|
impl<'tcx> SearchGraph<'tcx> {
|
|
pub fn deal_with_overflow(
|
|
&mut self,
|
|
tcx: TyCtxt<'tcx>,
|
|
goal: Canonical<'tcx, impl Sized>,
|
|
) -> QueryResult<'tcx> {
|
|
self.overflow_data.deal_with_overflow();
|
|
Ok(response_no_constraints_raw(tcx, goal.max_universe, goal.variables, Certainty::OVERFLOW))
|
|
}
|
|
}
|