only insert global predicates into the global cache once we've

completely proven them to be true
This commit is contained in:
Niko Matsakis 2015-12-22 19:46:51 -05:00
parent ecaa1cbc9c
commit 2c3f0123e9
2 changed files with 28 additions and 37 deletions

View File

@ -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);
}
}

View File

@ -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,