rust/src/librustc/middle/reachable.rs

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// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// Finds items that are externally reachable, to determine which items
// need to have their metadata (and possibly their AST) serialized.
// All items that can be referred to through an exported name are
// reachable, and when a reachable thing is inline or generic, it
// makes all other generics or inline functions that it references
// reachable as well.
use core::prelude::*;
use core::iterator::IteratorUtil;
use middle::resolve;
use middle::ty;
use middle::typeck;
use core::hashmap::HashSet;
use syntax::ast::*;
use syntax::ast;
use syntax::ast_map;
use syntax::ast_util::def_id_of_def;
use syntax::attr;
use syntax::codemap;
use syntax::parse::token;
use syntax::visit::Visitor;
use syntax::visit;
// Returns true if the given set of attributes contains the `#[inline]`
// attribute.
fn attributes_specify_inlining(attrs: &[attribute]) -> bool {
attr::attrs_contains_name(attrs, "inline")
}
// Returns true if the given set of generics implies that the item it's
// associated with must be inlined.
fn generics_require_inlining(generics: &Generics) -> bool {
!generics.ty_params.is_empty()
}
// Returns true if the given item must be inlined because it may be
// monomorphized or it was marked with `#[inline]`. This will only return
// true for functions.
fn item_might_be_inlined(item: @item) -> bool {
if attributes_specify_inlining(item.attrs) {
return true
}
match item.node {
item_fn(_, _, _, ref generics, _) => {
generics_require_inlining(generics)
}
_ => false,
}
}
// Returns true if the given type method must be inlined because it may be
// monomorphized or it was marked with `#[inline]`.
fn ty_method_might_be_inlined(ty_method: &ty_method) -> bool {
attributes_specify_inlining(ty_method.attrs) ||
generics_require_inlining(&ty_method.generics)
}
// Returns true if the given trait method must be inlined because it may be
// monomorphized or it was marked with `#[inline]`.
fn trait_method_might_be_inlined(trait_method: &trait_method) -> bool {
match *trait_method {
required(ref ty_method) => ty_method_might_be_inlined(ty_method),
provided(_) => true
}
}
// The context we're in. If we're in a public context, then public symbols are
// marked reachable. If we're in a private context, then only trait
// implementations are marked reachable.
#[deriving(Eq)]
enum PrivacyContext {
PublicContext,
PrivateContext,
}
// Information needed while computing reachability.
struct ReachableContext {
// The type context.
tcx: ty::ctxt,
// The method map, which links node IDs of method call expressions to the
// methods they've been resolved to.
method_map: typeck::method_map,
// The set of items which must be exported in the linkage sense.
reachable_symbols: @mut HashSet<node_id>,
// A worklist of item IDs. Each item ID in this worklist will be inlined
// and will be scanned for further references.
worklist: @mut ~[node_id],
}
impl ReachableContext {
// Creates a new reachability computation context.
fn new(tcx: ty::ctxt, method_map: typeck::method_map)
-> ReachableContext {
ReachableContext {
tcx: tcx,
method_map: method_map,
reachable_symbols: @mut HashSet::new(),
worklist: @mut ~[],
}
}
// Step 1: Mark all public symbols, and add all public symbols that might
// be inlined to a worklist.
fn mark_public_symbols(&self, crate: @crate) {
let reachable_symbols = self.reachable_symbols;
let worklist = self.worklist;
let visitor = visit::mk_vt(@Visitor {
visit_item: |item, (privacy_context, visitor):
(PrivacyContext, visit::vt<PrivacyContext>)| {
match item.node {
item_fn(*) => {
if privacy_context == PublicContext {
reachable_symbols.insert(item.id);
}
if item_might_be_inlined(item) {
worklist.push(item.id)
}
}
item_struct(ref struct_def, _) => {
match struct_def.ctor_id {
Some(ctor_id) if
privacy_context == PublicContext => {
reachable_symbols.insert(ctor_id);
}
Some(_) | None => {}
}
}
item_enum(ref enum_def, _) => {
if privacy_context == PublicContext {
for enum_def.variants.each |variant| {
reachable_symbols.insert(variant.node.id);
}
}
}
item_impl(ref generics, trait_ref, _, ref methods) => {
// XXX(pcwalton): We conservatively assume any methods
// on a trait implementation are reachable, when this
// is not the case. We could be more precise by only
// treating implementations of reachable or cross-
// crate traits as reachable.
let should_be_considered_public = |method: @method| {
(method.vis == public &&
privacy_context == PublicContext) ||
trait_ref.is_some()
};
// Mark all public methods as reachable.
for methods.each |&method| {
if should_be_considered_public(method) {
reachable_symbols.insert(method.id);
}
}
if generics_require_inlining(generics) {
// If the impl itself has generics, add all public
// symbols to the worklist.
for methods.each |&method| {
if should_be_considered_public(method) {
worklist.push(method.id)
}
}
} else {
// Otherwise, add only public methods that have
// generics to the worklist.
for methods.each |method| {
let generics = &method.generics;
let attrs = &method.attrs;
if generics_require_inlining(generics) ||
attributes_specify_inlining(*attrs) ||
should_be_considered_public(*method) {
worklist.push(method.id)
}
}
}
}
item_trait(_, _, ref trait_methods) => {
// Mark all provided methods as reachable.
if privacy_context == PublicContext {
for trait_methods.each |trait_method| {
match *trait_method {
provided(method) => {
reachable_symbols.insert(method.id);
worklist.push(method.id)
}
required(_) => {}
}
}
}
}
_ => {}
}
if item.vis == public && privacy_context == PublicContext {
visit::visit_item(item, (PublicContext, visitor))
} else {
visit::visit_item(item, (PrivateContext, visitor))
}
},
.. *visit::default_visitor()
});
visit::visit_crate(crate, (PublicContext, visitor))
}
// Returns true if the given def ID represents a local item that is
// eligible for inlining and false otherwise.
fn def_id_represents_local_inlined_item(tcx: ty::ctxt, def_id: def_id)
-> bool {
if def_id.crate != local_crate {
return false
}
let node_id = def_id.node;
match tcx.items.find(&node_id) {
Some(&ast_map::node_item(item, _)) => {
match item.node {
item_fn(*) => item_might_be_inlined(item),
_ => false,
}
}
Some(&ast_map::node_trait_method(trait_method, _, _)) => {
match *trait_method {
required(_) => false,
provided(_) => true,
}
}
Some(&ast_map::node_method(method, impl_did, _)) => {
if generics_require_inlining(&method.generics) ||
attributes_specify_inlining(method.attrs) {
true
} else {
// Check the impl. If the generics on the self type of the
// impl require inlining, this method does too.
assert!(impl_did.crate == local_crate);
match tcx.items.find(&impl_did.node) {
Some(&ast_map::node_item(item, _)) => {
match item.node {
item_impl(ref generics, _, _, _) => {
generics_require_inlining(generics)
}
_ => false
}
}
Some(_) => {
tcx.sess.span_bug(method.span,
"method is not inside an \
impl?!")
}
None => {
tcx.sess.span_bug(method.span,
"the impl that this method is \
supposedly inside of doesn't \
exist in the AST map?!")
}
}
}
}
Some(_) => false,
None => false // This will happen for default methods.
}
}
// Helper function to set up a visitor for `propagate()` below.
fn init_visitor(&self) -> visit::vt<()> {
let (worklist, method_map) = (self.worklist, self.method_map);
let (tcx, reachable_symbols) = (self.tcx, self.reachable_symbols);
visit::mk_vt(@visit::Visitor {
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visit_expr: |expr, (_, visitor)| {
match expr.node {
expr_path(_) => {
let def = match tcx.def_map.find(&expr.id) {
Some(&def) => def,
None => {
tcx.sess.span_bug(expr.span,
"def ID not in def map?!")
}
};
let def_id = def_id_of_def(def);
if ReachableContext::
def_id_represents_local_inlined_item(tcx,
def_id) {
worklist.push(def_id.node)
}
reachable_symbols.insert(def_id.node);
}
expr_method_call(*) => {
match method_map.find(&expr.id) {
Some(&typeck::method_map_entry {
origin: typeck::method_static(def_id),
_
}) => {
if ReachableContext::
def_id_represents_local_inlined_item(
tcx,
def_id) {
worklist.push(def_id.node)
}
reachable_symbols.insert(def_id.node);
}
Some(_) => {}
None => {
tcx.sess.span_bug(expr.span,
"method call expression \
not in method map?!")
}
}
}
_ => {}
}
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visit::visit_expr(expr, ((), visitor))
},
..*visit::default_visitor()
})
}
// Step 2: Mark all symbols that the symbols on the worklist touch.
fn propagate(&self) {
let visitor = self.init_visitor();
let mut scanned = HashSet::new();
while self.worklist.len() > 0 {
let search_item = self.worklist.pop();
if scanned.contains(&search_item) {
loop
}
scanned.insert(search_item);
self.reachable_symbols.insert(search_item);
// Find the AST block corresponding to the item and visit it,
// marking all path expressions that resolve to something
// interesting.
match self.tcx.items.find(&search_item) {
Some(&ast_map::node_item(item, _)) => {
match item.node {
item_fn(_, _, _, _, ref search_block) => {
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visit::visit_block(search_block, ((), visitor))
}
_ => {
self.tcx.sess.span_bug(item.span,
"found non-function item \
in worklist?!")
}
}
}
Some(&ast_map::node_trait_method(trait_method, _, _)) => {
match *trait_method {
required(ref ty_method) => {
self.tcx.sess.span_bug(ty_method.span,
"found required method in \
worklist?!")
}
provided(ref method) => {
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visit::visit_block(&method.body, ((), visitor))
}
}
}
Some(&ast_map::node_method(ref method, _, _)) => {
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visit::visit_block(&method.body, ((), visitor))
}
Some(_) => {
let ident_interner = token::get_ident_interner();
let desc = ast_map::node_id_to_str(self.tcx.items,
search_item,
ident_interner);
self.tcx.sess.bug(fmt!("found unexpected thingy in \
worklist: %s",
desc))
}
None => {
self.tcx.sess.bug(fmt!("found unmapped ID in worklist: \
%d",
search_item))
}
}
}
}
// Step 3: Mark all destructors as reachable.
//
// XXX(pcwalton): This is a conservative overapproximation, but fixing
// this properly would result in the necessity of computing *type*
// reachability, which might result in a compile time loss.
fn mark_destructors_reachable(&self) {
for self.tcx.destructor_for_type.each |_, destructor_def_id| {
if destructor_def_id.crate == local_crate {
self.reachable_symbols.insert(destructor_def_id.node);
}
}
}
}
pub fn find_reachable(tcx: ty::ctxt,
method_map: typeck::method_map,
crate: @crate)
-> @mut HashSet<node_id> {
// XXX(pcwalton): We only need to mark symbols that are exported. But this
// is more complicated than just looking at whether the symbol is `pub`,
// because it might be the target of a `pub use` somewhere. For now, I
// think we are fine, because you can't `pub use` something that wasn't
// exported due to the bug whereby `use` only looks through public
// modules even if you're inside the module the `use` appears in. When
// this bug is fixed, however, this code will need to be updated. Probably
// the easiest way to fix this (although a conservative overapproximation)
// is to have the name resolution pass mark all targets of a `pub use` as
// "must be reachable".
let reachable_context = ReachableContext::new(tcx, method_map);
// Step 1: Mark all public symbols, and add all public symbols that might
// be inlined to a worklist.
reachable_context.mark_public_symbols(crate);
// Step 2: Mark all symbols that the symbols on the worklist touch.
reachable_context.propagate();
// Step 3: Mark all destructors as reachable.
reachable_context.mark_destructors_reachable();
// Return the set of reachable symbols.
reachable_context.reachable_symbols
}