Only insert nodes which changes lint levels in the LintLevelMap

src/librustc/hir/map/mod.rs

@@ -1033,6 +1033,7 @@ impl<'hir> Map<'hir> {
     pub fn attrs(&self, id: NodeId) -> &'hir [ast::Attribute] {
         self.read(id); // reveals attributes on the node
         let attrs = match self.find(id) {
+            Some(Node::Local(l)) => Some(&l.attrs[..]),
             Some(Node::Item(i)) => Some(&i.attrs[..]),
             Some(Node::ForeignItem(fi)) => Some(&fi.attrs[..]),
             Some(Node::TraitItem(ref ti)) => Some(&ti.attrs[..]),

src/librustc/lint/levels.rs

@@ -157,6 +157,7 @@ pub struct LintLevelsBuilder<'a> {
 
 pub struct BuilderPush {
     prev: u32,
+    pub(super) changed: bool,
 }
 
 impl<'a> LintLevelsBuilder<'a> {
@@ -454,6 +455,7 @@ impl<'a> LintLevelsBuilder<'a> {
 
         BuilderPush {
             prev: prev,
+            changed: prev != self.cur,
         }
     }
 
@@ -512,11 +514,6 @@ impl LintLevelMap {
             self.sets.get_lint_level(lint, *idx, None, session)
         })
     }
-
-    /// Returns if this `id` has lint level information.
-    pub fn lint_level_set(&self, id: HirId) -> Option<u32> {
-        self.id_to_set.get(&id).cloned()
-    }
 }
 
 impl<'a> HashStable<StableHashingContext<'a>> for LintLevelMap {

src/librustc/lint/mod.rs

@@ -721,6 +721,16 @@ pub fn struct_lint_level<'a>(sess: &'a Session,
     return err
 }
 
+pub fn maybe_lint_level_root(tcx: TyCtxt<'_, '_, '_>, id: hir::HirId) -> bool {
+    let attrs = tcx.hir().attrs_by_hir_id(id);
+    for attr in attrs {
+        if Level::from_str(&attr.name().as_str()).is_some() {
+            true;
+        }
+    }
+    false
+}
+
 fn lint_levels<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, cnum: CrateNum)
     -> Lrc<LintLevelMap>
 {
@@ -731,9 +741,10 @@ fn lint_levels<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, cnum: CrateNum)
     };
     let krate = tcx.hir().krate();
 
-    builder.with_lint_attrs(hir::CRATE_HIR_ID, &krate.attrs, |builder| {
-        intravisit::walk_crate(builder, krate);
-    });
+    let push = builder.levels.push(&krate.attrs);
+    builder.levels.register_id(hir::CRATE_HIR_ID);
+    intravisit::walk_crate(&mut builder, krate);
+    builder.levels.pop(push);
 
     Lrc::new(builder.levels.build_map())
 }
@@ -751,7 +762,9 @@ impl<'a, 'tcx> LintLevelMapBuilder<'a, 'tcx> {
         where F: FnOnce(&mut Self)
     {
         let push = self.levels.push(attrs);
-        self.levels.register_id(id);
+        if push.changed {
+            self.levels.register_id(id);
+        }
         f(self);
         self.levels.pop(push);
     }

src/librustc/ty/context.rs

@@ -2856,30 +2856,44 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         err.emit()
     }
 
-    pub fn lint_level_at_node(self, lint: &'static Lint, mut id: hir::HirId)
-        -> (lint::Level, lint::LintSource)
-    {
-        // Right now we insert a `with_ignore` node in the dep graph here to
-        // ignore the fact that `lint_levels` below depends on the entire crate.
-        // For now this'll prevent false positives of recompiling too much when
-        // anything changes.
-        //
-        // Once red/green incremental compilation lands we should be able to
-        // remove this because while the crate changes often the lint level map
-        // will change rarely.
-        self.dep_graph.with_ignore(|| {
-            let sets = self.lint_levels(LOCAL_CRATE);
-            loop {
-                if let Some(pair) = sets.level_and_source(lint, id, self.sess) {
-                    return pair
-                }
-                let next = self.hir().get_parent_node_by_hir_id(id);
-                if next == id {
-                    bug!("lint traversal reached the root of the crate");
-                }
-                id = next;
+    /// Walks upwards from `id` to find a node which might change lint levels with attributes.
+    /// It stops at `bound` and just returns it if reached.
+    pub fn maybe_lint_level_root_bounded(
+        self,
+        mut id: hir::HirId,
+        bound: hir::HirId,
+    ) -> hir::HirId {
+        loop {
+            if id == bound {
+                return bound;
             }
-        })
+            if lint::maybe_lint_level_root(self, id) {
+                return id;
+            }
+            let next = self.hir().get_parent_node_by_hir_id(id);
+            if next == id {
+                bug!("lint traversal reached the root of the crate");
+            }
+            id = next;
+        }
+    }
+
+    pub fn lint_level_at_node(
+        self,
+        lint: &'static Lint,
+        mut id: hir::HirId
+    ) -> (lint::Level, lint::LintSource) {
+        let sets = self.lint_levels(LOCAL_CRATE);
+        loop {
+            if let Some(pair) = sets.level_and_source(lint, id, self.sess) {
+                return pair
+            }
+            let next = self.hir().get_parent_node_by_hir_id(id);
+            if next == id {
+                bug!("lint traversal reached the root of the crate");
+            }
+            id = next;
+        }
     }
 
     pub fn struct_span_lint_hir<S: Into<MultiSpan>>(self,

src/librustc_mir/build/scope.rs

@@ -82,7 +82,6 @@ use crate::hair::LintLevel;
 use rustc::middle::region;
 use rustc::ty::Ty;
 use rustc::hir;
-use rustc::hir::def_id::LOCAL_CRATE;
 use rustc::mir::*;
 use syntax_pos::{Span};
 use rustc_data_structures::fx::FxHashMap;
@@ -309,16 +308,25 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
         let source_scope = self.source_scope;
         let tcx = self.hir.tcx();
         if let LintLevel::Explicit(current_hir_id) = lint_level {
-            let same_lint_scopes = tcx.dep_graph.with_ignore(|| {
-                let sets = tcx.lint_levels(LOCAL_CRATE);
-                let parent_hir_id = self.source_scope_local_data[source_scope].lint_root;
-                sets.lint_level_set(parent_hir_id) == sets.lint_level_set(current_hir_id)
-            });
-
-            if !same_lint_scopes {
-                self.source_scope =
-                    self.new_source_scope(region_scope.1.span, lint_level,
-                                          None);
+            // Use `maybe_lint_level_root_bounded` with `root_lint_level` as a bound
+            // to avoid adding Hir dependences on our parents.
+            // We estimate the true lint roots here to avoid creating a lot of source scopes.
+
+            let parent_root = tcx.maybe_lint_level_root_bounded(
+                self.source_scope_local_data[source_scope].lint_root,
+                self.hir.root_lint_level,
+            );
+            let current_root = tcx.maybe_lint_level_root_bounded(
+                current_hir_id,
+                self.hir.root_lint_level
+            );
+
+            if parent_root != current_root {
+                self.source_scope = self.new_source_scope(
+                    region_scope.1.span,
+                    LintLevel::Explicit(current_root),
+                    None
+                );
             }
         }
         self.push_scope(region_scope);

src/librustc_mir/hair/cx/block.rs

@@ -103,7 +103,7 @@ fn mirror_stmts<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
                         },
                         pattern,
                         initializer: local.init.to_ref(),
-                        lint_level: cx.lint_level_of(local.hir_id),
+                        lint_level: LintLevel::Explicit(local.hir_id),
                     },
                     opt_destruction_scope: opt_dxn_ext,
                     span: stmt_span,

src/librustc_mir/hair/cx/expr.rs

@@ -45,7 +45,7 @@ impl<'tcx> Mirror<'tcx> for &'tcx hir::Expr {
             kind: ExprKind::Scope {
                 region_scope: expr_scope,
                 value: expr.to_ref(),
-                lint_level: cx.lint_level_of(self.hir_id),
+                lint_level: LintLevel::Explicit(self.hir_id),
             },
         };
 

src/librustc_mir/hair/cx/mod.rs

@@ -6,7 +6,7 @@ use crate::hair::*;
 use crate::hair::util::UserAnnotatedTyHelpers;
 
 use rustc_data_structures::indexed_vec::Idx;
-use rustc::hir::def_id::{DefId, LOCAL_CRATE};
+use rustc::hir::def_id::DefId;
 use rustc::hir::Node;
 use rustc::middle::region;
 use rustc::infer::InferCtxt;
@@ -76,11 +76,10 @@ impl<'a, 'gcx, 'tcx> Cx<'a, 'gcx, 'tcx> {
         // Constants always need overflow checks.
         check_overflow |= constness == hir::Constness::Const;
 
-        let lint_level = lint_level_for_hir_id(tcx, src_id);
         Cx {
             tcx,
             infcx,
-            root_lint_level: lint_level,
+            root_lint_level: src_id,
             param_env: tcx.param_env(src_def_id),
             identity_substs: InternalSubsts::identity_for_item(tcx.global_tcx(), src_def_id),
             region_scope_tree: tcx.region_scope_tree(src_def_id),
@@ -197,18 +196,6 @@ impl<'a, 'gcx, 'tcx> Cx<'a, 'gcx, 'tcx> {
         ty.needs_drop(self.tcx.global_tcx(), param_env)
     }
 
-    fn lint_level_of(&self, hir_id: hir::HirId) -> LintLevel {
-        let has_lint_level = self.tcx.dep_graph.with_ignore(|| {
-            self.tcx.lint_levels(LOCAL_CRATE).lint_level_set(hir_id).is_some()
-        });
-
-        if has_lint_level {
-            LintLevel::Explicit(hir_id)
-        } else {
-            LintLevel::Inherited
-        }
-    }
-
     pub fn tcx(&self) -> TyCtxt<'a, 'gcx, 'tcx> {
         self.tcx
     }
@@ -236,30 +223,6 @@ impl UserAnnotatedTyHelpers<'gcx, 'tcx> for Cx<'_, 'gcx, 'tcx> {
     }
 }
 
-fn lint_level_for_hir_id(tcx: TyCtxt<'_, '_, '_>, mut id: hir::HirId) -> hir::HirId {
-    // Right now we insert a `with_ignore` node in the dep graph here to
-    // ignore the fact that `lint_levels` below depends on the entire crate.
-    // For now this'll prevent false positives of recompiling too much when
-    // anything changes.
-    //
-    // Once red/green incremental compilation lands we should be able to
-    // remove this because while the crate changes often the lint level map
-    // will change rarely.
-    tcx.dep_graph.with_ignore(|| {
-        let sets = tcx.lint_levels(LOCAL_CRATE);
-        loop {
-            if sets.lint_level_set(id).is_some() {
-                return id
-            }
-            let next = tcx.hir().get_parent_node_by_hir_id(id);
-            if next == id {
-                bug!("lint traversal reached the root of the crate");
-            }
-            id = next;
-        }
-    })
-}
-
 mod block;
 mod expr;
 mod to_ref;