Avoid over-counting of UsePath in the HIR stats.

Author: nnethercote

compiler/rustc_passes/src/input_stats.rs

@@ -426,10 +426,16 @@ impl<'v> hir_visit::Visitor<'v> for StatCollector<'v> {
         hir_visit::walk_fn(self, fk, fd, b, id)
     }
 
-    fn visit_use(&mut self, p: &'v hir::UsePath<'v>, hir_id: HirId) {
+    fn visit_use(&mut self, p: &'v hir::UsePath<'v>, _hir_id: HirId) {
         // This is `visit_use`, but the type is `Path` so record it that way.
         self.record("Path", None, p);
-        hir_visit::walk_use(self, p, hir_id)
+        // Don't call `hir_visit::walk_use(self, p, hir_id)`: it calls
+        // `visit_path` up to three times, once for each namespace result in
+        // `p.res`, by building temporary `Path`s that are not part of the real
+        // HIR, which causes `p` to be double- or triple-counted. Instead just
+        // walk the path internals (i.e. the segments) directly.
+        let hir::Path { span: _, res: _, segments } = *p;
+        ast_visit::walk_list!(self, visit_path_segment, segments);
     }
 
     fn visit_trait_item(&mut self, ti: &'v hir::TraitItem<'v>) {

tests/ui/stats/input-stats.stderr

@@ -171,8 +171,8 @@ hir-stats - Impl                      88 (NN.N%)             1
 hir-stats - Trait                     88 (NN.N%)             1
 hir-stats - Fn                       176 (NN.N%)             2
 hir-stats - Use                      352 (NN.N%)             4
-hir-stats Path                   1_240 (NN.N%)            31            40
-hir-stats PathSegment            1_920 (NN.N%)            40            48
+hir-stats Path                   1_040 (NN.N%)            26            40
+hir-stats PathSegment            1_776 (NN.N%)            37            48
 hir-stats ----------------------------------------------------------------
-hir-stats Total                  8_988                   180
+hir-stats Total                  8_644                   172
 hir-stats