src/librustc/middle/reachable.rs

   1 // Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 // Finds items that are externally reachable, to determine which items
  12 // need to have their metadata (and possibly their AST) serialized.
  13 // All items that can be referred to through an exported name are
  14 // reachable, and when a reachable thing is inline or generic, it
  15 // makes all other generics or inline functions that it references
  16 // reachable as well.
  17
  18 use dep_graph::DepNode;
  19 use hir::map as ast_map;
  20 use hir::def::Def;
  21 use hir::def_id::DefId;
  22 use ty::{self, TyCtxt};
  23 use middle::privacy;
  24 use session::config;
  25 use util::nodemap::NodeSet;
  26
  27 use std::collections::HashSet;
  28 use syntax::abi::Abi;
  29 use syntax::ast;
  30 use syntax::attr;
  31 use hir;
  32 use hir::intravisit::Visitor;
  33 use hir::intravisit;
  34
  35 // Returns true if the given set of generics implies that the item it's
  36 // associated with must be inlined.
  37 fn generics_require_inlining(generics: &hir::Generics) -> bool {
  38     !generics.ty_params.is_empty()
  39 }
  40
  41 // Returns true if the given item must be inlined because it may be
  42 // monomorphized or it was marked with `#[inline]`. This will only return
  43 // true for functions.
  44 fn item_might_be_inlined(item: &hir::Item) -> bool {
  45     if attr::requests_inline(&item.attrs) {
  46         return true
  47     }
  48
  49     match item.node {
  50         hir::ItemImpl(_, _, ref generics, _, _, _) |
  51         hir::ItemFn(_, _, _, _, ref generics, _) => {
  52             generics_require_inlining(generics)
  53         }
  54         _ => false,
  55     }
  56 }
  57
  58 fn method_might_be_inlined(tcx: &TyCtxt, sig: &hir::MethodSig,
  59                            impl_item: &hir::ImplItem,
  60                            impl_src: DefId) -> bool {
  61     if attr::requests_inline(&impl_item.attrs) ||
  62         generics_require_inlining(&sig.generics) {
  63         return true
  64     }
  65     if let Some(impl_node_id) = tcx.map.as_local_node_id(impl_src) {
  66         match tcx.map.find(impl_node_id) {
  67             Some(ast_map::NodeItem(item)) =>
  68                 item_might_be_inlined(&item),
  69             Some(..) | None =>
  70                 span_bug!(impl_item.span, "impl did is not an item")
  71         }
  72     } else {
  73         span_bug!(impl_item.span, "found a foreign impl as a parent of a local method")
  74     }
  75 }
  76
  77 // Information needed while computing reachability.
  78 struct ReachableContext<'a, 'tcx: 'a> {
  79     // The type context.
  80     tcx: &'a TyCtxt<'tcx>,
  81     // The set of items which must be exported in the linkage sense.
  82     reachable_symbols: NodeSet,
  83     // A worklist of item IDs. Each item ID in this worklist will be inlined
  84     // and will be scanned for further references.
  85     worklist: Vec<ast::NodeId>,
  86     // Whether any output of this compilation is a library
  87     any_library: bool,
  88 }
  89
  90 impl<'a, 'tcx, 'v> Visitor<'v> for ReachableContext<'a, 'tcx> {
  91     fn visit_expr(&mut self, expr: &hir::Expr) {
  92         match expr.node {
  93             hir::ExprPath(..) => {
  94                 let def = match self.tcx.def_map.borrow().get(&expr.id) {
  95                     Some(d) => d.full_def(),
  96                     None => {
  97                         span_bug!(expr.span, "def ID not in def map?!")
  98                     }
  99                 };
 100
 101                 let def_id = def.def_id();
 102                 if let Some(node_id) = self.tcx.map.as_local_node_id(def_id) {
 103                     if self.def_id_represents_local_inlined_item(def_id) {
 104                         self.worklist.push(node_id);
 105                     } else {
 106                         match def {
 107                             // If this path leads to a constant, then we need to
 108                             // recurse into the constant to continue finding
 109                             // items that are reachable.
 110                             Def::Const(..) | Def::AssociatedConst(..) => {
 111                                 self.worklist.push(node_id);
 112                             }
 113
 114                             // If this wasn't a static, then the destination is
 115                             // surely reachable.
 116                             _ => {
 117                                 self.reachable_symbols.insert(node_id);
 118                             }
 119                         }
 120                     }
 121                 }
 122             }
 123             hir::ExprMethodCall(..) => {
 124                 let method_call = ty::MethodCall::expr(expr.id);
 125                 let def_id = self.tcx.tables.borrow().method_map[&method_call].def_id;
 126
 127                 // Mark the trait item (and, possibly, its default impl) as reachable
 128                 // Or mark inherent impl item as reachable
 129                 if let Some(node_id) = self.tcx.map.as_local_node_id(def_id) {
 130                     if self.def_id_represents_local_inlined_item(def_id) {
 131                         self.worklist.push(node_id)
 132                     }
 133                     self.reachable_symbols.insert(node_id);
 134                 }
 135             }
 136             _ => {}
 137         }
 138
 139         intravisit::walk_expr(self, expr)
 140     }
 141 }
 142
 143 impl<'a, 'tcx> ReachableContext<'a, 'tcx> {
 144     // Creates a new reachability computation context.
 145     fn new(tcx: &'a TyCtxt<'tcx>) -> ReachableContext<'a, 'tcx> {
 146         let any_library = tcx.sess.crate_types.borrow().iter().any(|ty| {
 147             *ty != config::CrateTypeExecutable
 148         });
 149         ReachableContext {
 150             tcx: tcx,
 151             reachable_symbols: NodeSet(),
 152             worklist: Vec::new(),
 153             any_library: any_library,
 154         }
 155     }
 156
 157     // Returns true if the given def ID represents a local item that is
 158     // eligible for inlining and false otherwise.
 159     fn def_id_represents_local_inlined_item(&self, def_id: DefId) -> bool {
 160         let node_id = match self.tcx.map.as_local_node_id(def_id) {
 161             Some(node_id) => node_id,
 162             None => { return false; }
 163         };
 164
 165         match self.tcx.map.find(node_id) {
 166             Some(ast_map::NodeItem(item)) => {
 167                 match item.node {
 168                     hir::ItemFn(..) => item_might_be_inlined(&item),
 169                     _ => false,
 170                 }
 171             }
 172             Some(ast_map::NodeTraitItem(trait_method)) => {
 173                 match trait_method.node {
 174                     hir::ConstTraitItem(_, ref default) => default.is_some(),
 175                     hir::MethodTraitItem(_, ref body) => body.is_some(),
 176                     hir::TypeTraitItem(..) => false,
 177                 }
 178             }
 179             Some(ast_map::NodeImplItem(impl_item)) => {
 180                 match impl_item.node {
 181                     hir::ImplItemKind::Const(..) => true,
 182                     hir::ImplItemKind::Method(ref sig, _) => {
 183                         if generics_require_inlining(&sig.generics) ||
 184                                 attr::requests_inline(&impl_item.attrs) {
 185                             true
 186                         } else {
 187                             let impl_did = self.tcx
 188                                                .map
 189                                                .get_parent_did(node_id);
 190                             // Check the impl. If the generics on the self
 191                             // type of the impl require inlining, this method
 192                             // does too.
 193                             let impl_node_id = self.tcx.map.as_local_node_id(impl_did).unwrap();
 194                             match self.tcx.map.expect_item(impl_node_id).node {
 195                                 hir::ItemImpl(_, _, ref generics, _, _, _) => {
 196                                     generics_require_inlining(generics)
 197                                 }
 198                                 _ => false
 199                             }
 200                         }
 201                     }
 202                     hir::ImplItemKind::Type(_) => false,
 203                 }
 204             }
 205             Some(_) => false,
 206             None => false   // This will happen for default methods.
 207         }
 208     }
 209
 210     // Step 2: Mark all symbols that the symbols on the worklist touch.
 211     fn propagate(&mut self) {
 212         let mut scanned = HashSet::new();
 213         loop {
 214             let search_item = match self.worklist.pop() {
 215                 Some(item) => item,
 216                 None => break,
 217             };
 218             if !scanned.insert(search_item) {
 219                 continue
 220             }
 221
 222             if let Some(ref item) = self.tcx.map.find(search_item) {
 223                 self.propagate_node(item, search_item);
 224             }
 225         }
 226     }
 227
 228     fn propagate_node(&mut self, node: &ast_map::Node,
 229                       search_item: ast::NodeId) {
 230         if !self.any_library {
 231             // If we are building an executable, only explicitly extern
 232             // types need to be exported.
 233             if let ast_map::NodeItem(item) = *node {
 234                 let reachable = if let hir::ItemFn(_, _, _, abi, _, _) = item.node {
 235                     abi != Abi::Rust
 236                 } else {
 237                     false
 238                 };
 239                 let is_extern = attr::contains_extern_indicator(&self.tcx.sess.diagnostic(),
 240                                                                 &item.attrs);
 241                 if reachable || is_extern {
 242                     self.reachable_symbols.insert(search_item);
 243                 }
 244             }
 245         } else {
 246             // If we are building a library, then reachable symbols will
 247             // continue to participate in linkage after this product is
 248             // produced. In this case, we traverse the ast node, recursing on
 249             // all reachable nodes from this one.
 250             self.reachable_symbols.insert(search_item);
 251         }
 252
 253         match *node {
 254             ast_map::NodeItem(item) => {
 255                 match item.node {
 256                     hir::ItemFn(_, _, _, _, _, ref search_block) => {
 257                         if item_might_be_inlined(&item) {
 258                             intravisit::walk_block(self, &search_block)
 259                         }
 260                     }
 261
 262                     // Reachable constants will be inlined into other crates
 263                     // unconditionally, so we need to make sure that their
 264                     // contents are also reachable.
 265                     hir::ItemConst(_, ref init) => {
 266                         self.visit_expr(&init);
 267                     }
 268
 269                     // These are normal, nothing reachable about these
 270                     // inherently and their children are already in the
 271                     // worklist, as determined by the privacy pass
 272                     hir::ItemExternCrate(_) | hir::ItemUse(_) |
 273                     hir::ItemTy(..) | hir::ItemStatic(_, _, _) |
 274                     hir::ItemMod(..) | hir::ItemForeignMod(..) |
 275                     hir::ItemImpl(..) | hir::ItemTrait(..) |
 276                     hir::ItemStruct(..) | hir::ItemEnum(..) |
 277                     hir::ItemDefaultImpl(..) => {}
 278                 }
 279             }
 280             ast_map::NodeTraitItem(trait_method) => {
 281                 match trait_method.node {
 282                     hir::ConstTraitItem(_, None) |
 283                     hir::MethodTraitItem(_, None) => {
 284                         // Keep going, nothing to get exported
 285                     }
 286                     hir::ConstTraitItem(_, Some(ref expr)) => {
 287                         self.visit_expr(&expr);
 288                     }
 289                     hir::MethodTraitItem(_, Some(ref body)) => {
 290                         intravisit::walk_block(self, body);
 291                     }
 292                     hir::TypeTraitItem(..) => {}
 293                 }
 294             }
 295             ast_map::NodeImplItem(impl_item) => {
 296                 match impl_item.node {
 297                     hir::ImplItemKind::Const(_, ref expr) => {
 298                         self.visit_expr(&expr);
 299                     }
 300                     hir::ImplItemKind::Method(ref sig, ref body) => {
 301                         let did = self.tcx.map.get_parent_did(search_item);
 302                         if method_might_be_inlined(self.tcx, sig, impl_item, did) {
 303                             intravisit::walk_block(self, body)
 304                         }
 305                     }
 306                     hir::ImplItemKind::Type(_) => {}
 307                 }
 308             }
 309             // Nothing to recurse on for these
 310             ast_map::NodeForeignItem(_) |
 311             ast_map::NodeVariant(_) |
 312             ast_map::NodeStructCtor(_) => {}
 313             _ => {
 314                 bug!("found unexpected thingy in worklist: {}",
 315                      self.tcx.map.node_to_string(search_item))
 316             }
 317         }
 318     }
 319 }
 320
 321 // Some methods from non-exported (completely private) trait impls still have to be
 322 // reachable if they are called from inlinable code. Generally, it's not known until
 323 // monomorphization if a specific trait impl item can be reachable or not. So, we
 324 // conservatively mark all of them as reachable.
 325 // FIXME: One possible strategy for pruning the reachable set is to avoid marking impl
 326 // items of non-exported traits (or maybe all local traits?) unless their respective
 327 // trait items are used from inlinable code through method call syntax or UFCS, or their
 328 // trait is a lang item.
 329 struct CollectPrivateImplItemsVisitor<'a> {
 330     access_levels: &'a privacy::AccessLevels,
 331     worklist: &'a mut Vec<ast::NodeId>,
 332 }
 333
 334 impl<'a, 'v> Visitor<'v> for CollectPrivateImplItemsVisitor<'a> {
 335     fn visit_item(&mut self, item: &hir::Item) {
 336         // We need only trait impls here, not inherent impls, and only non-exported ones
 337         if let hir::ItemImpl(_, _, _, Some(_), _, ref impl_items) = item.node {
 338             if !self.access_levels.is_reachable(item.id) {
 339                 for impl_item in impl_items {
 340                     self.worklist.push(impl_item.id);
 341                 }
 342             }
 343         }
 344     }
 345 }
 346
 347 pub fn find_reachable(tcx: &TyCtxt,
 348                       access_levels: &privacy::AccessLevels)
 349                       -> NodeSet {
 350     let _task = tcx.dep_graph.in_task(DepNode::Reachability);
 351
 352     let mut reachable_context = ReachableContext::new(tcx);
 353
 354     // Step 1: Seed the worklist with all nodes which were found to be public as
 355     //         a result of the privacy pass along with all local lang items and impl items.
 356     //         If other crates link to us, they're going to expect to be able to
 357     //         use the lang items, so we need to be sure to mark them as
 358     //         exported.
 359     for (id, _) in &access_levels.map {
 360         reachable_context.worklist.push(*id);
 361     }
 362     for item in tcx.lang_items.items().iter() {
 363         if let Some(did) = *item {
 364             if let Some(node_id) = tcx.map.as_local_node_id(did) {
 365                 reachable_context.worklist.push(node_id);
 366             }
 367         }
 368     }
 369     {
 370         let mut collect_private_impl_items = CollectPrivateImplItemsVisitor {
 371             access_levels: access_levels,
 372             worklist: &mut reachable_context.worklist,
 373         };
 374         tcx.map.krate().visit_all_items(&mut collect_private_impl_items);
 375     }
 376
 377     // Step 2: Mark all symbols that the symbols on the worklist touch.
 378     reachable_context.propagate();
 379
 380     // Return the set of reachable symbols.
 381     reachable_context.reachable_symbols
 382 }