Fix performance regression in LintLevelsBuilder

Author: michaelwoerister

compiler/rustc_data_structures/src/unord.rs

@@ -159,6 +159,7 @@ impl<T, I: Iterator<Item = T>> UnordItems<T, I> {
         self.collect_stable_ord_by_key(project_to_key)
     }
 
+    #[inline]
     pub fn collect_sorted<HCX, C>(self, hcx: &HCX, cache_sort_key: bool) -> C
     where
         T: ToStableHashKey<HCX>,
@@ -178,6 +179,7 @@ impl<T, I: Iterator<Item = T>> UnordItems<T, I> {
         items
     }
 
+    #[inline]
     pub fn collect_stable_ord_by_key<K, C, P>(self, project_to_key: P) -> C
     where
         K: StableCompare,

compiler/rustc_lint/src/levels.rs

@@ -1027,7 +1027,13 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
             }
         }
 
-        if !is_crate_node {
+        if !is_crate_node
+            // Make sure we filter before collecting and sorting, so we don't
+            // waste time stabilizing the iteration order only to throw it away
+            && self.current_specs().items().any(|(id, (_, src))| {
+                id.lint.crate_level_only && matches!(src, LintLevelSource::Node { .. })
+            })
+        {
             for (id, &(level, ref src)) in self.current_specs().to_sorted_stable_ord() {
                 if !id.lint.crate_level_only {
                     continue;