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Short-circuit some trivially const Drop types

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This commit is contained in:
Michael Goulet 2022-01-18 17:01:52 -08:00
parent 33e5efbd58
commit ba87be05cf
2 changed files with 45 additions and 10 deletions
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19
compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs
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@ -146,15 +146,10 @@ impl Qualif for NeedsNonConstDrop {
qualifs.needs_non_const_drop
}
fn in_any_value_of_ty<'tcx>(cx: &ConstCx<'_, 'tcx>, mut ty: Ty<'tcx>) -> bool {
// Avoid selecting for simple cases.
match ty::util::needs_drop_components(ty, &cx.tcx.data_layout).as_deref() {
Ok([]) => return false,
Err(ty::util::AlwaysRequiresDrop) => return true,
// If we've got a single component, select with that
// to increase the chance that we hit the selection cache.
Ok([t]) => ty = t,
Ok([..]) => {}
fn in_any_value_of_ty<'tcx>(cx: &ConstCx<'_, 'tcx>, ty: Ty<'tcx>) -> bool {
// Avoid selecting for simple cases, such as builtin types.
if ty::util::trivial_const_drop(ty) {
return false;
}
let Some(drop_trait) = cx.tcx.lang_items().drop_trait() else {
@ -187,11 +182,15 @@ impl Qualif for NeedsNonConstDrop {
impl_src,
ImplSource::ConstDrop(_) | ImplSource::Param(_, ty::BoundConstness::ConstIfConst)
) {
// If our const drop candidate is not ConstDrop or implied by param,
// If our const drop candidate is not ConstDrop or implied by the param env,
// then it's bad
return true;
}
if impl_src.borrow_nested_obligations().is_empty() {
return false;
}
// If we successfully found one, then select all of the predicates
// implied by our const drop impl.
let mut fcx = FulfillmentContext::new();