only insert global predicates into the global cache once we've
completely proven them to be true
This commit is contained in:
parent
ecaa1cbc9c
commit
2c3f0123e9
@ -86,8 +86,6 @@ pub struct FulfillmentContext<'tcx> {
|
||||
// obligations (otherwise, it's easy to fail to walk to a
|
||||
// particular node-id).
|
||||
region_obligations: NodeMap<Vec<RegionObligation<'tcx>>>,
|
||||
|
||||
pub errors_will_be_reported: bool,
|
||||
}
|
||||
|
||||
#[derive(Clone)]
|
||||
@ -105,28 +103,11 @@ pub struct PendingPredicateObligation<'tcx> {
|
||||
|
||||
impl<'tcx> FulfillmentContext<'tcx> {
|
||||
/// Creates a new fulfillment context.
|
||||
///
|
||||
/// `errors_will_be_reported` indicates whether ALL errors that
|
||||
/// are generated by this fulfillment context will be reported to
|
||||
/// the end user. This is used to inform caching, because it
|
||||
/// allows us to conclude that traits that resolve successfully
|
||||
/// will in fact always resolve successfully (in particular, it
|
||||
/// guarantees that if some dependent obligation encounters a
|
||||
/// problem, compilation will be aborted). If you're not sure of
|
||||
/// the right value here, pass `false`, as that is the more
|
||||
/// conservative option.
|
||||
///
|
||||
/// FIXME -- a better option would be to hold back on modifying
|
||||
/// the global cache until we know that all dependent obligations
|
||||
/// are also satisfied. In that case, we could actually remove
|
||||
/// this boolean flag, and we'd also avoid the problem of squelching
|
||||
/// duplicate errors that occur across fns.
|
||||
pub fn new(errors_will_be_reported: bool) -> FulfillmentContext<'tcx> {
|
||||
pub fn new() -> FulfillmentContext<'tcx> {
|
||||
FulfillmentContext {
|
||||
duplicate_set: FulfilledPredicates::new(),
|
||||
predicates: ObligationForest::new(),
|
||||
region_obligations: NodeMap(),
|
||||
errors_will_be_reported: errors_will_be_reported,
|
||||
}
|
||||
}
|
||||
|
||||
@ -250,23 +231,27 @@ impl<'tcx> FulfillmentContext<'tcx> {
|
||||
tcx: &ty::ctxt<'tcx>,
|
||||
predicate: &ty::Predicate<'tcx>)
|
||||
-> bool {
|
||||
// This is a kind of dirty hack to allow us to avoid "rederiving"
|
||||
// things that we have already proven in other methods.
|
||||
//
|
||||
// The idea is that any predicate that doesn't involve type
|
||||
// parameters and which only involves the 'static region (and
|
||||
// no other regions) is universally solvable, since impls are global.
|
||||
//
|
||||
// This is particularly important since even if we have a
|
||||
// cache hit in the selection context, we still wind up
|
||||
// evaluating the 'nested obligations'. This cache lets us
|
||||
// skip those.
|
||||
|
||||
if self.errors_will_be_reported && predicate.is_global() {
|
||||
tcx.fulfilled_predicates.borrow_mut().is_duplicate_or_add(predicate)
|
||||
} else {
|
||||
self.duplicate_set.is_duplicate_or_add(predicate)
|
||||
// For "global" predicates -- that is, predicates that don't
|
||||
// involve type parameters, inference variables, or regions
|
||||
// other than 'static -- we can check the cache in the tcx,
|
||||
// which allows us to leverage work from other threads. Note
|
||||
// that we don't add anything to this cache yet (unlike the
|
||||
// local cache). This is because the tcx cache maintains the
|
||||
// invariant that it only contains things that have been
|
||||
// proven, and we have not yet proven that `predicate` holds.
|
||||
if predicate.is_global() && tcx.fulfilled_predicates.borrow().is_duplicate(predicate) {
|
||||
return true;
|
||||
}
|
||||
|
||||
// If `predicate` is not global, or not present in the tcx
|
||||
// cache, we can still check for it in our local cache and add
|
||||
// it if not present. Note that if we find this predicate in
|
||||
// the local cache we can stop immediately, without reporting
|
||||
// any errors, even though we don't know yet if it is
|
||||
// true. This is because, while we don't yet know if the
|
||||
// predicate holds, we know that this same fulfillment context
|
||||
// already is in the process of finding out.
|
||||
self.duplicate_set.is_duplicate_or_add(predicate)
|
||||
}
|
||||
|
||||
/// Attempts to select obligations using `selcx`. If `only_new_obligations` is true, then it
|
||||
@ -294,6 +279,12 @@ impl<'tcx> FulfillmentContext<'tcx> {
|
||||
|
||||
debug!("select_where_possible: outcome={:?}", outcome);
|
||||
|
||||
// these are obligations that were proven to be true.
|
||||
for pending_obligation in outcome.successful {
|
||||
let predicate = &pending_obligation.obligation.predicate;
|
||||
if predicate.is_global() {
|
||||
selcx.tcx().fulfilled_predicates.borrow_mut()
|
||||
.is_duplicate_or_add(predicate);
|
||||
}
|
||||
}
|
||||
|
||||
|
@ -139,7 +139,7 @@ fn test_env<F>(source_string: &str,
|
||||
lang_items,
|
||||
stability::Index::new(krate),
|
||||
|tcx| {
|
||||
let infcx = infer::new_infer_ctxt(tcx, &tcx.tables, None, false);
|
||||
let infcx = infer::new_infer_ctxt(tcx, &tcx.tables, None);
|
||||
body(Env { infcx: &infcx });
|
||||
let free_regions = FreeRegionMap::new();
|
||||
infcx.resolve_regions_and_report_errors(&free_regions,
|
||||
|
Loading…
x
Reference in New Issue
Block a user