Fix lint perf regressions

compiler/rustc_lint/src/early.rs

@@ -20,23 +20,23 @@ use rustc_ast::ptr::P;
 use rustc_ast::visit::{self as ast_visit, Visitor};
 use rustc_ast::{self as ast, walk_list, HasAttrs};
 use rustc_middle::ty::RegisteredTools;
-use rustc_session::lint::{BufferedEarlyLint, LintBuffer};
+use rustc_session::lint::{BufferedEarlyLint, LintBuffer, LintPass};
 use rustc_session::Session;
 use rustc_span::symbol::Ident;
 use rustc_span::Span;
 
-macro_rules! run_early_passes { ($cx:expr, $f:ident, $($args:expr),*) => ({
-    for pass in $cx.passes.iter_mut() {
-        pass.$f(&$cx.context, $($args),*);
-    }
+macro_rules! lint_callback { ($cx:expr, $f:ident, $($args:expr),*) => ({
+    $cx.pass.$f(&$cx.context, $($args),*);
 }) }
 
-pub struct EarlyContextAndPasses<'a> {
+/// Implements the AST traversal for early lint passes. `T` provides the the
+/// `check_*` methods.
+pub struct EarlyContextAndPass<'a, T: EarlyLintPass> {
     context: EarlyContext<'a>,
-    passes: Vec<EarlyLintPassObject>,
+    pass: T,
 }
 
-impl<'a> EarlyContextAndPasses<'a> {
+impl<'a, T: EarlyLintPass> EarlyContextAndPass<'a, T> {
     // This always-inlined function is for the hot call site.
     #[inline(always)]
     fn inlined_check_id(&mut self, id: ast::NodeId) {
@@ -70,27 +70,27 @@ impl<'a> EarlyContextAndPasses<'a> {
 
         self.inlined_check_id(id);
         debug!("early context: enter_attrs({:?})", attrs);
-        run_early_passes!(self, enter_lint_attrs, attrs);
+        lint_callback!(self, enter_lint_attrs, attrs);
         f(self);
         debug!("early context: exit_attrs({:?})", attrs);
-        run_early_passes!(self, exit_lint_attrs, attrs);
+        lint_callback!(self, exit_lint_attrs, attrs);
         self.context.builder.pop(push);
     }
 }
 
-impl<'a> ast_visit::Visitor<'a> for EarlyContextAndPasses<'a> {
+impl<'a, T: EarlyLintPass> ast_visit::Visitor<'a> for EarlyContextAndPass<'a, T> {
     fn visit_param(&mut self, param: &'a ast::Param) {
         self.with_lint_attrs(param.id, &param.attrs, |cx| {
-            run_early_passes!(cx, check_param, param);
+            lint_callback!(cx, check_param, param);
             ast_visit::walk_param(cx, param);
         });
     }
 
     fn visit_item(&mut self, it: &'a ast::Item) {
         self.with_lint_attrs(it.id, &it.attrs, |cx| {
-            run_early_passes!(cx, check_item, it);
+            lint_callback!(cx, check_item, it);
             ast_visit::walk_item(cx, it);
-            run_early_passes!(cx, check_item_post, it);
+            lint_callback!(cx, check_item_post, it);
         })
     }
 
@@ -101,10 +101,10 @@ impl<'a> ast_visit::Visitor<'a> for EarlyContextAndPasses<'a> {
     }
 
     fn visit_pat(&mut self, p: &'a ast::Pat) {
-        run_early_passes!(self, check_pat, p);
+        lint_callback!(self, check_pat, p);
         self.check_id(p.id);
         ast_visit::walk_pat(self, p);
-        run_early_passes!(self, check_pat_post, p);
+        lint_callback!(self, check_pat_post, p);
     }
 
     fn visit_pat_field(&mut self, field: &'a ast::PatField) {
@@ -120,7 +120,7 @@ impl<'a> ast_visit::Visitor<'a> for EarlyContextAndPasses<'a> {
 
     fn visit_expr(&mut self, e: &'a ast::Expr) {
         self.with_lint_attrs(e.id, &e.attrs, |cx| {
-            run_early_passes!(cx, check_expr, e);
+            lint_callback!(cx, check_expr, e);
             ast_visit::walk_expr(cx, e);
         })
     }
@@ -141,7 +141,7 @@ impl<'a> ast_visit::Visitor<'a> for EarlyContextAndPasses<'a> {
         // Note that statements get their attributes from
         // the AST struct that they wrap (e.g. an item)
         self.with_lint_attrs(s.id, s.attrs(), |cx| {
-            run_early_passes!(cx, check_stmt, s);
+            lint_callback!(cx, check_stmt, s);
             cx.check_id(s.id);
         });
         // The visitor for the AST struct wrapped
@@ -152,7 +152,7 @@ impl<'a> ast_visit::Visitor<'a> for EarlyContextAndPasses<'a> {
     }
 
     fn visit_fn(&mut self, fk: ast_visit::FnKind<'a>, span: Span, id: ast::NodeId) {
-        run_early_passes!(self, check_fn, fk, span, id);
+        lint_callback!(self, check_fn, fk, span, id);
         self.check_id(id);
         ast_visit::walk_fn(self, fk);
 
@@ -180,37 +180,37 @@ impl<'a> ast_visit::Visitor<'a> for EarlyContextAndPasses<'a> {
 
     fn visit_variant(&mut self, v: &'a ast::Variant) {
         self.with_lint_attrs(v.id, &v.attrs, |cx| {
-            run_early_passes!(cx, check_variant, v);
+            lint_callback!(cx, check_variant, v);
             ast_visit::walk_variant(cx, v);
         })
     }
 
     fn visit_ty(&mut self, t: &'a ast::Ty) {
-        run_early_passes!(self, check_ty, t);
+        lint_callback!(self, check_ty, t);
         self.check_id(t.id);
         ast_visit::walk_ty(self, t);
     }
 
     fn visit_ident(&mut self, ident: Ident) {
-        run_early_passes!(self, check_ident, ident);
+        lint_callback!(self, check_ident, ident);
     }
 
     fn visit_local(&mut self, l: &'a ast::Local) {
         self.with_lint_attrs(l.id, &l.attrs, |cx| {
-            run_early_passes!(cx, check_local, l);
+            lint_callback!(cx, check_local, l);
             ast_visit::walk_local(cx, l);
         })
     }
 
     fn visit_block(&mut self, b: &'a ast::Block) {
-        run_early_passes!(self, check_block, b);
+        lint_callback!(self, check_block, b);
         self.check_id(b.id);
         ast_visit::walk_block(self, b);
     }
 
     fn visit_arm(&mut self, a: &'a ast::Arm) {
         self.with_lint_attrs(a.id, &a.attrs, |cx| {
-            run_early_passes!(cx, check_arm, a);
+            lint_callback!(cx, check_arm, a);
             ast_visit::walk_arm(cx, a);
         })
     }
@@ -229,19 +229,19 @@ impl<'a> ast_visit::Visitor<'a> for EarlyContextAndPasses<'a> {
     }
 
     fn visit_generic_arg(&mut self, arg: &'a ast::GenericArg) {
-        run_early_passes!(self, check_generic_arg, arg);
+        lint_callback!(self, check_generic_arg, arg);
         ast_visit::walk_generic_arg(self, arg);
     }
 
     fn visit_generic_param(&mut self, param: &'a ast::GenericParam) {
         self.with_lint_attrs(param.id, &param.attrs, |cx| {
-            run_early_passes!(cx, check_generic_param, param);
+            lint_callback!(cx, check_generic_param, param);
             ast_visit::walk_generic_param(cx, param);
         });
     }
 
     fn visit_generics(&mut self, g: &'a ast::Generics) {
-        run_early_passes!(self, check_generics, g);
+        lint_callback!(self, check_generics, g);
         ast_visit::walk_generics(self, g);
     }
 
@@ -250,18 +250,18 @@ impl<'a> ast_visit::Visitor<'a> for EarlyContextAndPasses<'a> {
     }
 
     fn visit_poly_trait_ref(&mut self, t: &'a ast::PolyTraitRef) {
-        run_early_passes!(self, check_poly_trait_ref, t);
+        lint_callback!(self, check_poly_trait_ref, t);
         ast_visit::walk_poly_trait_ref(self, t);
     }
 
     fn visit_assoc_item(&mut self, item: &'a ast::AssocItem, ctxt: ast_visit::AssocCtxt) {
         self.with_lint_attrs(item.id, &item.attrs, |cx| match ctxt {
             ast_visit::AssocCtxt::Trait => {
-                run_early_passes!(cx, check_trait_item, item);
+                lint_callback!(cx, check_trait_item, item);
                 ast_visit::walk_assoc_item(cx, item, ctxt);
             }
             ast_visit::AssocCtxt::Impl => {
-                run_early_passes!(cx, check_impl_item, item);
+                lint_callback!(cx, check_impl_item, item);
                 ast_visit::walk_assoc_item(cx, item, ctxt);
             }
         });
@@ -282,28 +282,57 @@ impl<'a> ast_visit::Visitor<'a> for EarlyContextAndPasses<'a> {
     }
 
     fn visit_attribute(&mut self, attr: &'a ast::Attribute) {
-        run_early_passes!(self, check_attribute, attr);
+        lint_callback!(self, check_attribute, attr);
     }
 
     fn visit_mac_def(&mut self, mac: &'a ast::MacroDef, id: ast::NodeId) {
-        run_early_passes!(self, check_mac_def, mac);
+        lint_callback!(self, check_mac_def, mac);
         self.check_id(id);
     }
 
     fn visit_mac_call(&mut self, mac: &'a ast::MacCall) {
-        run_early_passes!(self, check_mac, mac);
+        lint_callback!(self, check_mac, mac);
         ast_visit::walk_mac(self, mac);
     }
 }
 
+// Combines multiple lint passes into a single pass, at runtime. Each
+// `check_foo` method in `$methods` within this pass simply calls `check_foo`
+// once per `$pass`. Compare with `declare_combined_early_lint_pass`, which is
+// similar, but combines lint passes at compile time.
+struct RuntimeCombinedEarlyLintPass<'a> {
+    passes: &'a mut [EarlyLintPassObject],
+}
+
+#[allow(rustc::lint_pass_impl_without_macro)]
+impl LintPass for RuntimeCombinedEarlyLintPass<'_> {
+    fn name(&self) -> &'static str {
+        panic!()
+    }
+}
+
+macro_rules! impl_early_lint_pass {
+    ([], [$($(#[$attr:meta])* fn $f:ident($($param:ident: $arg:ty),*);)*]) => (
+        impl EarlyLintPass for RuntimeCombinedEarlyLintPass<'_> {
+            $(fn $f(&mut self, context: &EarlyContext<'_>, $($param: $arg),*) {
+                for pass in self.passes.iter_mut() {
+                    pass.$f(context, $($param),*);
+                }
+            })*
+        }
+    )
+}
+
+crate::early_lint_methods!(impl_early_lint_pass, []);
+
 /// Early lints work on different nodes - either on the crate root, or on freshly loaded modules.
 /// This trait generalizes over those nodes.
 pub trait EarlyCheckNode<'a>: Copy {
     fn id(self) -> ast::NodeId;
     fn attrs<'b>(self) -> &'b [ast::Attribute]
     where
         'a: 'b;
-    fn check<'b>(self, cx: &mut EarlyContextAndPasses<'b>)
+    fn check<'b, T: EarlyLintPass>(self, cx: &mut EarlyContextAndPass<'b, T>)
     where
         'a: 'b;
 }
@@ -318,13 +347,13 @@ impl<'a> EarlyCheckNode<'a> for &'a ast::Crate {
     {
         &self.attrs
     }
-    fn check<'b>(self, cx: &mut EarlyContextAndPasses<'b>)
+    fn check<'b, T: EarlyLintPass>(self, cx: &mut EarlyContextAndPass<'b, T>)
     where
         'a: 'b,
     {
-        run_early_passes!(cx, check_crate, self);
+        lint_callback!(cx, check_crate, self);
         ast_visit::walk_crate(cx, self);
-        run_early_passes!(cx, check_crate_post, self);
+        lint_callback!(cx, check_crate_post, self);
     }
 }
 
@@ -338,7 +367,7 @@ impl<'a> EarlyCheckNode<'a> for (ast::NodeId, &'a [ast::Attribute], &'a [P<ast::
     {
         self.1
     }
-    fn check<'b>(self, cx: &mut EarlyContextAndPasses<'b>)
+    fn check<'b, T: EarlyLintPass>(self, cx: &mut EarlyContextAndPass<'b, T>)
     where
         'a: 'b,
     {
@@ -356,21 +385,37 @@ pub fn check_ast_node<'a>(
     builtin_lints: impl EarlyLintPass + 'static,
     check_node: impl EarlyCheckNode<'a>,
 ) {
+    let context = EarlyContext::new(
+        sess,
+        !pre_expansion,
+        lint_store,
+        registered_tools,
+        lint_buffer.unwrap_or_default(),
+    );
+
+    // Note: `passes` is often empty. In that case, it's faster to run
+    // `builtin_lints` directly rather than bundling it up into the
+    // `RuntimeCombinedEarlyLintPass`.
     let passes =
         if pre_expansion { &lint_store.pre_expansion_passes } else { &lint_store.early_passes };
-    let mut passes: Vec<EarlyLintPassObject> = passes.iter().map(|p| (p)()).collect();
-    passes.push(Box::new(builtin_lints));
-
-    let mut cx = EarlyContextAndPasses {
-        context: EarlyContext::new(
-            sess,
-            !pre_expansion,
-            lint_store,
-            registered_tools,
-            lint_buffer.unwrap_or_default(),
-        ),
-        passes,
-    };
+    if passes.is_empty() {
+        check_ast_node_inner(sess, check_node, context, builtin_lints);
+    } else {
+        let mut passes: Vec<_> = passes.iter().map(|mk_pass| (mk_pass)()).collect();
+        passes.push(Box::new(builtin_lints));
+        let pass = RuntimeCombinedEarlyLintPass { passes: &mut passes[..] };
+        check_ast_node_inner(sess, check_node, context, pass);
+    }
+}
+
+pub fn check_ast_node_inner<'a, T: EarlyLintPass>(
+    sess: &Session,
+    check_node: impl EarlyCheckNode<'a>,
+    context: EarlyContext<'_>,
+    pass: T,
+) {
+    let mut cx = EarlyContextAndPass { context, pass };
+
     cx.with_lint_attrs(check_node.id(), check_node.attrs(), |cx| check_node.check(cx));
 
     // All of the buffered lints should have been emitted at this point.