Add a second level to the AST size reporting.

This tells you which variants of the enums are most common, which is
very useful. I've only done it for the AST for now, HIR can be done
later.

compiler/rustc_passes/src/hir_stats.rs

@@ -21,11 +21,28 @@ enum Id {
     None,
 }
 
-struct NodeData {
+struct NodeStats {
     count: usize,
     size: usize,
 }
 
+impl NodeStats {
+    fn new() -> NodeStats {
+        NodeStats { count: 0, size: 0 }
+    }
+}
+
+struct Node {
+    stats: NodeStats,
+    subnodes: FxHashMap<&'static str, NodeStats>,
+}
+
+impl Node {
+    fn new() -> Node {
+        Node { stats: NodeStats::new(), subnodes: FxHashMap::default() }
+    }
+}
+
 /// This type measures the size of AST and HIR nodes, by implementing the AST
 /// and HIR `Visitor` traits. But we don't measure every visited type because
 /// that could cause double counting.
@@ -45,14 +62,14 @@ struct NodeData {
 /// unfortunate.
 struct StatCollector<'k> {
     krate: Option<Map<'k>>,
-    data: FxHashMap<&'static str, NodeData>,
+    nodes: FxHashMap<&'static str, Node>,
     seen: FxHashSet<Id>,
 }
 
 pub fn print_hir_stats(tcx: TyCtxt<'_>) {
     let mut collector = StatCollector {
         krate: Some(tcx.hir()),
-        data: FxHashMap::default(),
+        nodes: FxHashMap::default(),
         seen: FxHashSet::default(),
     };
     tcx.hir().walk_toplevel_module(&mut collector);
@@ -64,47 +81,82 @@ pub fn print_ast_stats(krate: &ast::Crate, title: &str) {
     use rustc_ast::visit::Visitor;
 
     let mut collector =
-        StatCollector { krate: None, data: FxHashMap::default(), seen: FxHashSet::default() };
+        StatCollector { krate: None, nodes: FxHashMap::default(), seen: FxHashSet::default() };
     collector.visit_crate(krate);
     collector.print(title);
 }
 
 impl<'k> StatCollector<'k> {
-    fn record<T>(&mut self, label: &'static str, id: Id, node: &T) {
+    // Record a top-level node.
+    fn record<T>(&mut self, label: &'static str, id: Id, val: &T) {
+        self.record_inner(label, None, id, val);
+    }
+
+    // Record a two-level entry, with a top-level enum type and a variant.
+    fn record_variant<T>(&mut self, label1: &'static str, label2: &'static str, id: Id, val: &T) {
+        self.record_inner(label1, Some(label2), id, val);
+    }
+
+    fn record_inner<T>(
+        &mut self,
+        label1: &'static str,
+        label2: Option<&'static str>,
+        id: Id,
+        val: &T,
+    ) {
         if id != Id::None && !self.seen.insert(id) {
             return;
         }
 
-        let entry = self.data.entry(label).or_insert(NodeData { count: 0, size: 0 });
+        let node = self.nodes.entry(label1).or_insert(Node::new());
+        node.stats.count += 1;
+        node.stats.size = std::mem::size_of_val(val);
 
-        entry.count += 1;
-        entry.size = std::mem::size_of_val(node);
+        if let Some(label2) = label2 {
+            let subnode = node.subnodes.entry(label2).or_insert(NodeStats::new());
+            subnode.count += 1;
+            subnode.size = std::mem::size_of_val(val);
+        }
     }
 
     fn print(&self, title: &str) {
-        let mut stats: Vec<_> = self.data.iter().collect();
-
-        stats.sort_by_key(|&(_, ref d)| d.count * d.size);
+        let mut nodes: Vec<_> = self.nodes.iter().collect();
+        nodes.sort_by_key(|&(_, ref node)| node.stats.count * node.stats.size);
 
-        let total_size = stats.iter().map(|(_, data)| data.count * data.size).sum();
+        let total_size = nodes.iter().map(|(_, node)| node.stats.count * node.stats.size).sum();
 
         eprintln!("\n{}\n", title);
 
         eprintln!("{:<18}{:>18}{:>14}{:>14}", "Name", "Accumulated Size", "Count", "Item Size");
         eprintln!("----------------------------------------------------------------");
 
-        let percent = |m, n| { (m * 100) as f64 / n as f64 };
+        let percent = |m, n| (m * 100) as f64 / n as f64;
 
-        for (label, data) in stats {
-            let size = data.count * data.size;
+        for (label, node) in nodes {
+            let size = node.stats.count * node.stats.size;
             eprintln!(
                 "{:<18}{:>10} ({:4.1}%){:>14}{:>14}",
                 label,
                 to_readable_str(size),
                 percent(size, total_size),
-                to_readable_str(data.count),
-                to_readable_str(data.size)
+                to_readable_str(node.stats.count),
+                to_readable_str(node.stats.size)
             );
+            if !node.subnodes.is_empty() {
+                let mut subnodes: Vec<_> = node.subnodes.iter().collect();
+                subnodes.sort_by_key(|&(_, ref subnode)| subnode.count * subnode.size);
+
+                for (label, subnode) in subnodes {
+                    let size = subnode.count * subnode.size;
+                    eprintln!(
+                        "- {:<18}{:>10} ({:4.1}%){:>14}",
+                        label,
+                        to_readable_str(size),
+                        percent(size, total_size),
+                        to_readable_str(subnode.count),
+                    );
+                }
+            }
         }
         eprintln!("----------------------------------------------------------------");
         eprintln!("{:<18}{:>10}\n", "Total", to_readable_str(total_size));
@@ -268,14 +320,54 @@ impl<'v> hir_visit::Visitor<'v> for StatCollector<'v> {
     }
 }
 
+// Used to avoid boilerplate for types with many variants.
+macro_rules! record_variants {
+    (
+        ($self:ident, $val:expr, $kind:expr, $ty:ty, $tykind:ident), // mandatory pieces
+        [$($variant:ident),*]
+    ) => {
+        match $kind {
+            $(
+                ast::$tykind::$variant { .. } => {
+                    $self.record_variant(stringify!($ty), stringify!($variant), Id::None, $val)
+                }
+            )*
+        }
+    };
+}
+
 impl<'v> ast_visit::Visitor<'v> for StatCollector<'v> {
     fn visit_foreign_item(&mut self, i: &'v ast::ForeignItem) {
-        self.record("ForeignItem", Id::None, i);
+        record_variants!(
+            (self, i, i.kind, ForeignItem, ForeignItemKind),
+            [Static, Fn, TyAlias, MacCall]
+        );
         ast_visit::walk_foreign_item(self, i)
     }
 
     fn visit_item(&mut self, i: &'v ast::Item) {
-        self.record("Item", Id::None, i);
+        record_variants!(
+            (self, i, i.kind, Item, ItemKind),
+            [
+                ExternCrate,
+                Use,
+                Static,
+                Const,
+                Fn,
+                Mod,
+                ForeignMod,
+                GlobalAsm,
+                TyAlias,
+                Enum,
+                Struct,
+                Union,
+                Trait,
+                TraitAlias,
+                Impl,
+                MacCall,
+                MacroDef
+            ]
+        );
         ast_visit::walk_item(self, i)
     }
 
@@ -290,7 +382,10 @@ impl<'v> ast_visit::Visitor<'v> for StatCollector<'v> {
     }
 
     fn visit_stmt(&mut self, s: &'v ast::Stmt) {
-        self.record("Stmt", Id::None, s);
+        record_variants!(
+            (self, s, s.kind, Stmt, StmtKind),
+            [Local, Item, Expr, Semi, Empty, MacCall]
+        );
         ast_visit::walk_stmt(self, s)
     }
 
@@ -305,17 +400,66 @@ impl<'v> ast_visit::Visitor<'v> for StatCollector<'v> {
     }
 
     fn visit_pat(&mut self, p: &'v ast::Pat) {
-        self.record("Pat", Id::None, p);
+        record_variants!(
+            (self, p, p.kind, Pat, PatKind),
+            [
+                Wild,
+                Ident,
+                Struct,
+                TupleStruct,
+                Or,
+                Path,
+                Tuple,
+                Box,
+                Ref,
+                Lit,
+                Range,
+                Slice,
+                Rest,
+                Paren,
+                MacCall
+            ]
+        );
         ast_visit::walk_pat(self, p)
     }
 
-    fn visit_expr(&mut self, ex: &'v ast::Expr) {
-        self.record("Expr", Id::None, ex);
-        ast_visit::walk_expr(self, ex)
+    fn visit_expr(&mut self, e: &'v ast::Expr) {
+        record_variants!(
+            (self, e, e.kind, Expr, ExprKind),
+            [
+                Box, Array, ConstBlock, Call, MethodCall, Tup, Binary, Unary, Lit, Cast, Type, Let,
+                If, While, ForLoop, Loop, Match, Closure, Block, Async, Await, TryBlock, Assign,
+                AssignOp, Field, Index, Range, Underscore, Path, AddrOf, Break, Continue, Ret,
+                InlineAsm, MacCall, Struct, Repeat, Paren, Try, Yield, Yeet, Err
+            ]
+        );
+        ast_visit::walk_expr(self, e)
     }
 
     fn visit_ty(&mut self, t: &'v ast::Ty) {
-        self.record("Ty", Id::None, t);
+        record_variants!(
+            (self, t, t.kind, Ty, TyKind),
+            [
+                Slice,
+                Array,
+                Ptr,
+                Rptr,
+                BareFn,
+                Never,
+                Tup,
+                Path,
+                TraitObject,
+                ImplTrait,
+                Paren,
+                Typeof,
+                Infer,
+                ImplicitSelf,
+                MacCall,
+                Err,
+                CVarArgs
+            ]
+        );
+
         ast_visit::walk_ty(self, t)
     }
 
@@ -325,7 +469,10 @@ impl<'v> ast_visit::Visitor<'v> for StatCollector<'v> {
     }
 
     fn visit_where_predicate(&mut self, p: &'v ast::WherePredicate) {
-        self.record("WherePredicate", Id::None, p);
+        record_variants!(
+            (self, p, p, WherePredicate, WherePredicate),
+            [BoundPredicate, RegionPredicate, EqPredicate]
+        );
         ast_visit::walk_where_predicate(self, p)
     }
 
@@ -334,14 +481,17 @@ impl<'v> ast_visit::Visitor<'v> for StatCollector<'v> {
         ast_visit::walk_fn(self, fk, s)
     }
 
-    fn visit_assoc_item(&mut self, item: &'v ast::AssocItem, ctxt: ast_visit::AssocCtxt) {
-        self.record("AssocItem", Id::None, item);
-        ast_visit::walk_assoc_item(self, item, ctxt);
+    fn visit_assoc_item(&mut self, i: &'v ast::AssocItem, ctxt: ast_visit::AssocCtxt) {
+        record_variants!(
+            (self, i, i.kind, AssocItem, AssocItemKind),
+            [Const, Fn, TyAlias, MacCall]
+        );
+        ast_visit::walk_assoc_item(self, i, ctxt);
     }
 
-    fn visit_param_bound(&mut self, bounds: &'v ast::GenericBound, _ctxt: BoundKind) {
-        self.record("GenericBound", Id::None, bounds);
-        ast_visit::walk_param_bound(self, bounds)
+    fn visit_param_bound(&mut self, b: &'v ast::GenericBound, _ctxt: BoundKind) {
+        record_variants!((self, b, b, GenericBound, GenericBound), [Trait, Outlives]);
+        ast_visit::walk_param_bound(self, b)
     }
 
     fn visit_field_def(&mut self, s: &'v ast::FieldDef) {
@@ -369,12 +519,12 @@ impl<'v> ast_visit::Visitor<'v> for StatCollector<'v> {
     // common, so we implement `visit_generic_args` and tolerate the double
     // counting in the former case.
     fn visit_generic_args(&mut self, sp: Span, g: &'v ast::GenericArgs) {
-        self.record("GenericArgs", Id::None, g);
+        record_variants!((self, g, g, GenericArgs, GenericArgs), [AngleBracketed, Parenthesized]);
         ast_visit::walk_generic_args(self, sp, g)
     }
 
     fn visit_attribute(&mut self, attr: &'v ast::Attribute) {
-        self.record("Attribute", Id::None, attr);
+        record_variants!((self, attr, attr.kind, Attribute, AttrKind), [Normal, DocComment]);
         ast_visit::walk_attribute(self, attr)
     }
 

src/test/ui/stats/hir-stats.rs

@@ -2,8 +2,8 @@
 // compile-flags: -Zhir-stats
 // only-x86_64
 
-// The aim here is to include at least one of every different type of AST/HIR
-// node reported by `-Zhir-stats`.
+// The aim here is to include at least one of every different type of top-level
+// AST/HIR node reported by `-Zhir-stats`.
 
 #![allow(dead_code)]