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rust/src/librustc/middle/region.rs
JP Sugarbroad 8611d857ed Clean up some info log spam.
2016-04-14 12:21:52 -07:00

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// Copyright 2012-2014 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.
//! This file actually contains two passes related to regions. The first
//! pass builds up the `scope_map`, which describes the parent links in
//! the region hierarchy. The second pass infers which types must be
//! region parameterized.
//!
//! Most of the documentation on regions can be found in
//! `middle/infer/region_inference/README.md`
use dep_graph::DepNode;
use hir::map as ast_map;
use session::Session;
use util::nodemap::{FnvHashMap, NodeMap, NodeSet};
use middle::cstore::InlinedItem;
use ty;
use std::cell::RefCell;
use std::collections::hash_map::Entry;
use std::fmt;
use std::mem;
use syntax::codemap::{self, Span};
use syntax::ast::{self, NodeId};
use hir;
use hir::intravisit::{self, Visitor, FnKind};
use hir::{Block, Item, FnDecl, Arm, Pat, PatKind, Stmt, Expr, Local};
#[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, RustcEncodable,
RustcDecodable, Copy)]
pub struct CodeExtent(u32);
impl fmt::Debug for CodeExtent {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "CodeExtent({:?}", self.0)?;
ty::tls::with_opt(|opt_tcx| {
if let Some(tcx) = opt_tcx {
if let Some(data) = tcx.region_maps.code_extents.borrow().get(self.0 as usize) {
write!(f, "/{:?}", data)?;
}
}
Ok(())
})?;
write!(f, ")")
}
}
/// The root of everything. I should be using NonZero or profiling
/// instead of this (probably).
pub const ROOT_CODE_EXTENT : CodeExtent = CodeExtent(0);
/// A placeholder used in trans to stand for real code extents
pub const DUMMY_CODE_EXTENT : CodeExtent = CodeExtent(1);
/// CodeExtent represents a statically-describable extent that can be
/// used to bound the lifetime/region for values.
///
/// `Misc(node_id)`: Any AST node that has any extent at all has the
/// `Misc(node_id)` extent. Other variants represent special cases not
/// immediately derivable from the abstract syntax tree structure.
///
/// `DestructionScope(node_id)` represents the extent of destructors
/// implicitly-attached to `node_id` that run immediately after the
/// expression for `node_id` itself. Not every AST node carries a
/// `DestructionScope`, but those that are `terminating_scopes` do;
/// see discussion with `RegionMaps`.
///
/// `Remainder(BlockRemainder { block, statement_index })` represents
/// the extent of user code running immediately after the initializer
/// expression for the indexed statement, until the end of the block.
///
/// So: the following code can be broken down into the extents beneath:
/// ```
/// let a = f().g( 'b: { let x = d(); let y = d(); x.h(y) } ) ;
/// ```
///
/// +-+ (D12.)
/// +-+ (D11.)
/// +---------+ (R10.)
/// +-+ (D9.)
/// +----------+ (M8.)
/// +----------------------+ (R7.)
/// +-+ (D6.)
/// +----------+ (M5.)
/// +-----------------------------------+ (M4.)
/// +--------------------------------------------------+ (M3.)
/// +--+ (M2.)
/// +-----------------------------------------------------------+ (M1.)
///
/// (M1.): Misc extent of the whole `let a = ...;` statement.
/// (M2.): Misc extent of the `f()` expression.
/// (M3.): Misc extent of the `f().g(..)` expression.
/// (M4.): Misc extent of the block labelled `'b:`.
/// (M5.): Misc extent of the `let x = d();` statement
/// (D6.): DestructionScope for temporaries created during M5.
/// (R7.): Remainder extent for block `'b:`, stmt 0 (let x = ...).
/// (M8.): Misc Extent of the `let y = d();` statement.
/// (D9.): DestructionScope for temporaries created during M8.
/// (R10.): Remainder extent for block `'b:`, stmt 1 (let y = ...).
/// (D11.): DestructionScope for temporaries and bindings from block `'b:`.
/// (D12.): DestructionScope for temporaries created during M1 (e.g. f()).
///
/// Note that while the above picture shows the destruction scopes
/// as following their corresponding misc extents, in the internal
/// data structures of the compiler the destruction scopes are
/// represented as enclosing parents. This is sound because we use the
/// enclosing parent relationship just to ensure that referenced
/// values live long enough; phrased another way, the starting point
/// of each range is not really the important thing in the above
/// picture, but rather the ending point.
///
/// FIXME (pnkfelix): This currently derives `PartialOrd` and `Ord` to
/// placate the same deriving in `ty::FreeRegion`, but we may want to
/// actually attach a more meaningful ordering to scopes than the one
/// generated via deriving here.
#[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, Debug, Copy)]
pub enum CodeExtentData {
Misc(ast::NodeId),
// extent of the call-site for a function or closure (outlives
// the parameters as well as the body).
CallSiteScope { fn_id: ast::NodeId, body_id: ast::NodeId },
// extent of parameters passed to a function or closure (they
// outlive its body)
ParameterScope { fn_id: ast::NodeId, body_id: ast::NodeId },
// extent of destructors for temporaries of node-id
DestructionScope(ast::NodeId),
// extent of code following a `let id = expr;` binding in a block
Remainder(BlockRemainder)
}
/// extent of call-site for a function/method.
#[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, RustcEncodable,
RustcDecodable, Debug, Copy)]
pub struct CallSiteScopeData {
pub fn_id: ast::NodeId, pub body_id: ast::NodeId,
}
impl CallSiteScopeData {
pub fn to_code_extent(&self, region_maps: &RegionMaps) -> CodeExtent {
region_maps.lookup_code_extent(
match *self {
CallSiteScopeData { fn_id, body_id } =>
CodeExtentData::CallSiteScope { fn_id: fn_id, body_id: body_id },
})
}
}
/// Represents a subscope of `block` for a binding that is introduced
/// by `block.stmts[first_statement_index]`. Such subscopes represent
/// a suffix of the block. Note that each subscope does not include
/// the initializer expression, if any, for the statement indexed by
/// `first_statement_index`.
///
/// For example, given `{ let (a, b) = EXPR_1; let c = EXPR_2; ... }`:
///
/// * the subscope with `first_statement_index == 0` is scope of both
/// `a` and `b`; it does not include EXPR_1, but does include
/// everything after that first `let`. (If you want a scope that
/// includes EXPR_1 as well, then do not use `CodeExtentData::Remainder`,
/// but instead another `CodeExtent` that encompasses the whole block,
/// e.g. `CodeExtentData::Misc`.
///
/// * the subscope with `first_statement_index == 1` is scope of `c`,
/// and thus does not include EXPR_2, but covers the `...`.
#[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, RustcEncodable,
RustcDecodable, Debug, Copy)]
pub struct BlockRemainder {
pub block: ast::NodeId,
pub first_statement_index: u32,
}
impl CodeExtentData {
/// Returns a node id associated with this scope.
///
/// NB: likely to be replaced as API is refined; e.g. pnkfelix
/// anticipates `fn entry_node_id` and `fn each_exit_node_id`.
pub fn node_id(&self) -> ast::NodeId {
match *self {
CodeExtentData::Misc(node_id) => node_id,
// These cases all return rough approximations to the
// precise extent denoted by `self`.
CodeExtentData::Remainder(br) => br.block,
CodeExtentData::DestructionScope(node_id) => node_id,
CodeExtentData::CallSiteScope { fn_id: _, body_id } |
CodeExtentData::ParameterScope { fn_id: _, body_id } => body_id,
}
}
}
impl CodeExtent {
#[inline]
fn into_option(self) -> Option<CodeExtent> {
if self == ROOT_CODE_EXTENT {
None
} else {
Some(self)
}
}
pub fn node_id(&self, region_maps: &RegionMaps) -> ast::NodeId {
region_maps.code_extent_data(*self).node_id()
}
/// Returns the span of this CodeExtent. Note that in general the
/// returned span may not correspond to the span of any node id in
/// the AST.
pub fn span(&self, region_maps: &RegionMaps, ast_map: &ast_map::Map) -> Option<Span> {
match ast_map.find(self.node_id(region_maps)) {
Some(ast_map::NodeBlock(ref blk)) => {
match region_maps.code_extent_data(*self) {
CodeExtentData::CallSiteScope { .. } |
CodeExtentData::ParameterScope { .. } |
CodeExtentData::Misc(_) |
CodeExtentData::DestructionScope(_) => Some(blk.span),
CodeExtentData::Remainder(r) => {
assert_eq!(r.block, blk.id);
// Want span for extent starting after the
// indexed statement and ending at end of
// `blk`; reuse span of `blk` and shift `lo`
// forward to end of indexed statement.
//
// (This is the special case aluded to in the
// doc-comment for this method)
let stmt_span = blk.stmts[r.first_statement_index as usize].span;
Some(Span { lo: stmt_span.hi, ..blk.span })
}
}
}
Some(ast_map::NodeExpr(ref expr)) => Some(expr.span),
Some(ast_map::NodeStmt(ref stmt)) => Some(stmt.span),
Some(ast_map::NodeItem(ref item)) => Some(item.span),
Some(_) | None => None,
}
}
}
/// The region maps encode information about region relationships.
pub struct RegionMaps {
code_extents: RefCell<Vec<CodeExtentData>>,
code_extent_interner: RefCell<FnvHashMap<CodeExtentData, CodeExtent>>,
/// `scope_map` maps from a scope id to the enclosing scope id;
/// this is usually corresponding to the lexical nesting, though
/// in the case of closures the parent scope is the innermost
/// conditional expression or repeating block. (Note that the
/// enclosing scope id for the block associated with a closure is
/// the closure itself.)
scope_map: RefCell<Vec<CodeExtent>>,
/// `var_map` maps from a variable or binding id to the block in
/// which that variable is declared.
var_map: RefCell<NodeMap<CodeExtent>>,
/// `rvalue_scopes` includes entries for those expressions whose cleanup scope is
/// larger than the default. The map goes from the expression id
/// to the cleanup scope id. For rvalues not present in this
/// table, the appropriate cleanup scope is the innermost
/// enclosing statement, conditional expression, or repeating
/// block (see `terminating_scopes`).
rvalue_scopes: RefCell<NodeMap<CodeExtent>>,
/// Encodes the hierarchy of fn bodies. Every fn body (including
/// closures) forms its own distinct region hierarchy, rooted in
/// the block that is the fn body. This map points from the id of
/// that root block to the id of the root block for the enclosing
/// fn, if any. Thus the map structures the fn bodies into a
/// hierarchy based on their lexical mapping. This is used to
/// handle the relationships between regions in a fn and in a
/// closure defined by that fn. See the "Modeling closures"
/// section of the README in infer::region_inference for
/// more details.
fn_tree: RefCell<NodeMap<ast::NodeId>>,
}
#[derive(Debug, Copy, Clone)]
pub struct Context {
/// the root of the current region tree. This is typically the id
/// of the innermost fn body. Each fn forms its own disjoint tree
/// in the region hierarchy. These fn bodies are themselves
/// arranged into a tree. See the "Modeling closures" section of
/// the README in infer::region_inference for more
/// details.
root_id: Option<ast::NodeId>,
/// the scope that contains any new variables declared
var_parent: CodeExtent,
/// region parent of expressions etc
parent: CodeExtent
}
struct RegionResolutionVisitor<'a> {
sess: &'a Session,
// Generated maps:
region_maps: &'a RegionMaps,
cx: Context,
/// `terminating_scopes` is a set containing the ids of each
/// statement, or conditional/repeating expression. These scopes
/// are calling "terminating scopes" because, when attempting to
/// find the scope of a temporary, by default we search up the
/// enclosing scopes until we encounter the terminating scope. A
/// conditional/repeating expression is one which is not
/// guaranteed to execute exactly once upon entering the parent
/// scope. This could be because the expression only executes
/// conditionally, such as the expression `b` in `a && b`, or
/// because the expression may execute many times, such as a loop
/// body. The reason that we distinguish such expressions is that,
/// upon exiting the parent scope, we cannot statically know how
/// many times the expression executed, and thus if the expression
/// creates temporaries we cannot know statically how many such
/// temporaries we would have to cleanup. Therefore we ensure that
/// the temporaries never outlast the conditional/repeating
/// expression, preventing the need for dynamic checks and/or
/// arbitrary amounts of stack space. Terminating scopes end
/// up being contained in a DestructionScope that contains the
/// destructor's execution.
terminating_scopes: NodeSet
}
impl RegionMaps {
/// create a bogus code extent for the regions in astencode types. Nobody
/// really cares about the contents of these.
pub fn bogus_code_extent(&self, e: CodeExtentData) -> CodeExtent {
self.intern_code_extent(e, DUMMY_CODE_EXTENT)
}
pub fn lookup_code_extent(&self, e: CodeExtentData) -> CodeExtent {
match self.code_extent_interner.borrow().get(&e) {
Some(&d) => d,
None => bug!("unknown code extent {:?}", e)
}
}
pub fn node_extent(&self, n: ast::NodeId) -> CodeExtent {
self.lookup_code_extent(CodeExtentData::Misc(n))
}
// Returns the code extent for an item - the destruction scope.
pub fn item_extent(&self, n: ast::NodeId) -> CodeExtent {
self.lookup_code_extent(CodeExtentData::DestructionScope(n))
}
pub fn call_site_extent(&self, fn_id: ast::NodeId, body_id: ast::NodeId) -> CodeExtent {
assert!(fn_id != body_id);
self.lookup_code_extent(CodeExtentData::CallSiteScope { fn_id: fn_id, body_id: body_id })
}
pub fn opt_destruction_extent(&self, n: ast::NodeId) -> Option<CodeExtent> {
self.code_extent_interner.borrow().get(&CodeExtentData::DestructionScope(n)).cloned()
}
pub fn intern_code_extent(&self,
e: CodeExtentData,
parent: CodeExtent) -> CodeExtent {
match self.code_extent_interner.borrow_mut().entry(e) {
Entry::Occupied(o) => {
// this can happen when the bogus code extents from tydecode
// have (bogus) NodeId-s that overlap items created during
// inlining.
// We probably shouldn't be creating bogus code extents
// though.
let idx = *o.get();
if parent == DUMMY_CODE_EXTENT {
info!("CodeExtent({}) = {:?} [parent={}] BOGUS!",
idx.0, e, parent.0);
} else {
assert_eq!(self.scope_map.borrow()[idx.0 as usize],
DUMMY_CODE_EXTENT);
info!("CodeExtent({}) = {:?} [parent={}] RECLAIMED!",
idx.0, e, parent.0);
self.scope_map.borrow_mut()[idx.0 as usize] = parent;
}
idx
}
Entry::Vacant(v) => {
if self.code_extents.borrow().len() > 0xffffffffusize {
bug!() // should pass a sess,
// but this isn't the only place
}
let idx = CodeExtent(self.code_extents.borrow().len() as u32);
debug!("CodeExtent({}) = {:?} [parent={}]", idx.0, e, parent.0);
self.code_extents.borrow_mut().push(e);
self.scope_map.borrow_mut().push(parent);
*v.insert(idx)
}
}
}
pub fn intern_node(&self,
n: ast::NodeId,
parent: CodeExtent) -> CodeExtent {
self.intern_code_extent(CodeExtentData::Misc(n), parent)
}
pub fn code_extent_data(&self, e: CodeExtent) -> CodeExtentData {
self.code_extents.borrow()[e.0 as usize]
}
pub fn each_encl_scope<E>(&self, mut e:E) where E: FnMut(&CodeExtent, &CodeExtent) {
for child_id in 1..self.code_extents.borrow().len() {
let child = CodeExtent(child_id as u32);
if let Some(parent) = self.opt_encl_scope(child) {
e(&child, &parent)
}
}
}
pub fn each_var_scope<E>(&self, mut e:E) where E: FnMut(&ast::NodeId, &CodeExtent) {
for (child, parent) in self.var_map.borrow().iter() {
e(child, parent)
}
}
pub fn each_rvalue_scope<E>(&self, mut e:E) where E: FnMut(&ast::NodeId, &CodeExtent) {
for (child, parent) in self.rvalue_scopes.borrow().iter() {
e(child, parent)
}
}
/// Records that `sub_fn` is defined within `sup_fn`. These ids
/// should be the id of the block that is the fn body, which is
/// also the root of the region hierarchy for that fn.
fn record_fn_parent(&self, sub_fn: ast::NodeId, sup_fn: ast::NodeId) {
debug!("record_fn_parent(sub_fn={:?}, sup_fn={:?})", sub_fn, sup_fn);
assert!(sub_fn != sup_fn);
let previous = self.fn_tree.borrow_mut().insert(sub_fn, sup_fn);
assert!(previous.is_none());
}
fn fn_is_enclosed_by(&self, mut sub_fn: ast::NodeId, sup_fn: ast::NodeId) -> bool {
let fn_tree = self.fn_tree.borrow();
loop {
if sub_fn == sup_fn { return true; }
match fn_tree.get(&sub_fn) {
Some(&s) => { sub_fn = s; }
None => { return false; }
}
}
}
fn record_var_scope(&self, var: ast::NodeId, lifetime: CodeExtent) {
debug!("record_var_scope(sub={:?}, sup={:?})", var, lifetime);
assert!(var != lifetime.node_id(self));
self.var_map.borrow_mut().insert(var, lifetime);
}
fn record_rvalue_scope(&self, var: ast::NodeId, lifetime: CodeExtent) {
debug!("record_rvalue_scope(sub={:?}, sup={:?})", var, lifetime);
assert!(var != lifetime.node_id(self));
self.rvalue_scopes.borrow_mut().insert(var, lifetime);
}
pub fn opt_encl_scope(&self, id: CodeExtent) -> Option<CodeExtent> {
//! Returns the narrowest scope that encloses `id`, if any.
self.scope_map.borrow()[id.0 as usize].into_option()
}
#[allow(dead_code)] // used in cfg
pub fn encl_scope(&self, id: CodeExtent) -> CodeExtent {
//! Returns the narrowest scope that encloses `id`, if any.
self.opt_encl_scope(id).unwrap()
}
/// Returns the lifetime of the local variable `var_id`
pub fn var_scope(&self, var_id: ast::NodeId) -> CodeExtent {
match self.var_map.borrow().get(&var_id) {
Some(&r) => r,
None => { bug!("no enclosing scope for id {:?}", var_id); }
}
}
pub fn temporary_scope(&self, expr_id: ast::NodeId) -> Option<CodeExtent> {
//! Returns the scope when temp created by expr_id will be cleaned up
// check for a designated rvalue scope
match self.rvalue_scopes.borrow().get(&expr_id) {
Some(&s) => {
debug!("temporary_scope({:?}) = {:?} [custom]", expr_id, s);
return Some(s);
}
None => { }
}
let scope_map : &[CodeExtent] = &self.scope_map.borrow();
let code_extents: &[CodeExtentData] = &self.code_extents.borrow();
// else, locate the innermost terminating scope
// if there's one. Static items, for instance, won't
// have an enclosing scope, hence no scope will be
// returned.
let expr_extent = self.node_extent(expr_id);
// For some reason, the expr's scope itself is skipped here.
let mut id = match scope_map[expr_extent.0 as usize].into_option() {
Some(i) => i,
_ => return None
};
while let Some(p) = scope_map[id.0 as usize].into_option() {
match code_extents[p.0 as usize] {
CodeExtentData::DestructionScope(..) => {
debug!("temporary_scope({:?}) = {:?} [enclosing]",
expr_id, id);
return Some(id);
}
_ => id = p
}
}
debug!("temporary_scope({:?}) = None", expr_id);
return None;
}
pub fn var_region(&self, id: ast::NodeId) -> ty::Region {
//! Returns the lifetime of the variable `id`.
let scope = ty::ReScope(self.var_scope(id));
debug!("var_region({:?}) = {:?}", id, scope);
scope
}
pub fn scopes_intersect(&self, scope1: CodeExtent, scope2: CodeExtent)
-> bool {
self.is_subscope_of(scope1, scope2) ||
self.is_subscope_of(scope2, scope1)
}
/// Returns true if `subscope` is equal to or is lexically nested inside `superscope` and false
/// otherwise.
pub fn is_subscope_of(&self,
subscope: CodeExtent,
superscope: CodeExtent)
-> bool {
let mut s = subscope;
debug!("is_subscope_of({:?}, {:?})", subscope, superscope);
while superscope != s {
match self.opt_encl_scope(s) {
None => {
debug!("is_subscope_of({:?}, {:?}, s={:?})=false",
subscope, superscope, s);
return false;
}
Some(scope) => s = scope
}
}
debug!("is_subscope_of({:?}, {:?})=true",
subscope, superscope);
return true;
}
/// Finds the nearest common ancestor (if any) of two scopes. That is, finds the smallest
/// scope which is greater than or equal to both `scope_a` and `scope_b`.
pub fn nearest_common_ancestor(&self,
scope_a: CodeExtent,
scope_b: CodeExtent)
-> CodeExtent {
if scope_a == scope_b { return scope_a; }
let mut a_buf: [CodeExtent; 32] = [ROOT_CODE_EXTENT; 32];
let mut a_vec: Vec<CodeExtent> = vec![];
let mut b_buf: [CodeExtent; 32] = [ROOT_CODE_EXTENT; 32];
let mut b_vec: Vec<CodeExtent> = vec![];
let scope_map : &[CodeExtent] = &self.scope_map.borrow();
let a_ancestors = ancestors_of(scope_map,
scope_a, &mut a_buf, &mut a_vec);
let b_ancestors = ancestors_of(scope_map,
scope_b, &mut b_buf, &mut b_vec);
let mut a_index = a_ancestors.len() - 1;
let mut b_index = b_ancestors.len() - 1;
// Here, [ab]_ancestors is a vector going from narrow to broad.
// The end of each vector will be the item where the scope is
// defined; if there are any common ancestors, then the tails of
// the vector will be the same. So basically we want to walk
// backwards from the tail of each vector and find the first point
// where they diverge. If one vector is a suffix of the other,
// then the corresponding scope is a superscope of the other.
if a_ancestors[a_index] != b_ancestors[b_index] {
// In this case, the two regions belong to completely
// different functions. Compare those fn for lexical
// nesting. The reasoning behind this is subtle. See the
// "Modeling closures" section of the README in
// infer::region_inference for more details.
let a_root_scope = self.code_extent_data(a_ancestors[a_index]);
let b_root_scope = self.code_extent_data(a_ancestors[a_index]);
return match (a_root_scope, b_root_scope) {
(CodeExtentData::DestructionScope(a_root_id),
CodeExtentData::DestructionScope(b_root_id)) => {
if self.fn_is_enclosed_by(a_root_id, b_root_id) {
// `a` is enclosed by `b`, hence `b` is the ancestor of everything in `a`
scope_b
} else if self.fn_is_enclosed_by(b_root_id, a_root_id) {
// `b` is enclosed by `a`, hence `a` is the ancestor of everything in `b`
scope_a
} else {
// neither fn encloses the other
bug!()
}
}
_ => {
// root ids are always Misc right now
bug!()
}
};
}
loop {
// Loop invariant: a_ancestors[a_index] == b_ancestors[b_index]
// for all indices between a_index and the end of the array
if a_index == 0 { return scope_a; }
if b_index == 0 { return scope_b; }
a_index -= 1;
b_index -= 1;
if a_ancestors[a_index] != b_ancestors[b_index] {
return a_ancestors[a_index + 1];
}
}
fn ancestors_of<'a>(scope_map: &[CodeExtent],
scope: CodeExtent,
buf: &'a mut [CodeExtent; 32],
vec: &'a mut Vec<CodeExtent>) -> &'a [CodeExtent] {
// debug!("ancestors_of(scope={:?})", scope);
let mut scope = scope;
let mut i = 0;
while i < 32 {
buf[i] = scope;
match scope_map[scope.0 as usize].into_option() {
Some(superscope) => scope = superscope,
_ => return &buf[..i+1]
}
i += 1;
}
*vec = Vec::with_capacity(64);
vec.extend_from_slice(buf);
loop {
vec.push(scope);
match scope_map[scope.0 as usize].into_option() {
Some(superscope) => scope = superscope,
_ => return &*vec
}
}
}
}
}
/// Records the lifetime of a local variable as `cx.var_parent`
fn record_var_lifetime(visitor: &mut RegionResolutionVisitor,
var_id: ast::NodeId,
_sp: Span) {
match visitor.cx.var_parent {
ROOT_CODE_EXTENT => {
// this can happen in extern fn declarations like
//
// extern fn isalnum(c: c_int) -> c_int
}
parent_scope =>
visitor.region_maps.record_var_scope(var_id, parent_scope),
}
}
fn resolve_block(visitor: &mut RegionResolutionVisitor, blk: &hir::Block) {
debug!("resolve_block(blk.id={:?})", blk.id);
let prev_cx = visitor.cx;
let block_extent = visitor.new_node_extent_with_dtor(blk.id);
// We treat the tail expression in the block (if any) somewhat
// differently from the statements. The issue has to do with
// temporary lifetimes. Consider the following:
//
// quux({
// let inner = ... (&bar()) ...;
//
// (... (&foo()) ...) // (the tail expression)
// }, other_argument());
//
// Each of the statements within the block is a terminating
// scope, and thus a temporary (e.g. the result of calling
// `bar()` in the initalizer expression for `let inner = ...;`)
// will be cleaned up immediately after its corresponding
// statement (i.e. `let inner = ...;`) executes.
//
// On the other hand, temporaries associated with evaluating the
// tail expression for the block are assigned lifetimes so that
// they will be cleaned up as part of the terminating scope
// *surrounding* the block expression. Here, the terminating
// scope for the block expression is the `quux(..)` call; so
// those temporaries will only be cleaned up *after* both
// `other_argument()` has run and also the call to `quux(..)`
// itself has returned.
visitor.cx = Context {
root_id: prev_cx.root_id,
var_parent: block_extent,
parent: block_extent,
};
{
// This block should be kept approximately in sync with
// `intravisit::walk_block`. (We manually walk the block, rather
// than call `walk_block`, in order to maintain precise
// index information.)
for (i, statement) in blk.stmts.iter().enumerate() {
if let hir::StmtDecl(..) = statement.node {
// Each StmtDecl introduces a subscope for bindings
// introduced by the declaration; this subscope covers
// a suffix of the block . Each subscope in a block
// has the previous subscope in the block as a parent,
// except for the first such subscope, which has the
// block itself as a parent.
let stmt_extent = visitor.new_code_extent(
CodeExtentData::Remainder(BlockRemainder {
block: blk.id,
first_statement_index: i as u32
})
);
visitor.cx = Context {
root_id: prev_cx.root_id,
var_parent: stmt_extent,
parent: stmt_extent,
};
}
visitor.visit_stmt(statement)
}
walk_list!(visitor, visit_expr, &blk.expr);
}
visitor.cx = prev_cx;
}
fn resolve_arm(visitor: &mut RegionResolutionVisitor, arm: &hir::Arm) {
visitor.terminating_scopes.insert(arm.body.id);
if let Some(ref expr) = arm.guard {
visitor.terminating_scopes.insert(expr.id);
}
intravisit::walk_arm(visitor, arm);
}
fn resolve_pat(visitor: &mut RegionResolutionVisitor, pat: &hir::Pat) {
visitor.new_node_extent(pat.id);
// If this is a binding (or maybe a binding, I'm too lazy to check
// the def map) then record the lifetime of that binding.
match pat.node {
PatKind::Ident(..) => {
record_var_lifetime(visitor, pat.id, pat.span);
}
_ => { }
}
intravisit::walk_pat(visitor, pat);
}
fn resolve_stmt(visitor: &mut RegionResolutionVisitor, stmt: &hir::Stmt) {
let stmt_id = stmt.node.id();
debug!("resolve_stmt(stmt.id={:?})", stmt_id);
// Every statement will clean up the temporaries created during
// execution of that statement. Therefore each statement has an
// associated destruction scope that represents the extent of the
// statement plus its destructors, and thus the extent for which
// regions referenced by the destructors need to survive.
visitor.terminating_scopes.insert(stmt_id);
let stmt_extent = visitor.new_node_extent_with_dtor(stmt_id);
let prev_parent = visitor.cx.parent;
visitor.cx.parent = stmt_extent;
intravisit::walk_stmt(visitor, stmt);
visitor.cx.parent = prev_parent;
}
fn resolve_expr(visitor: &mut RegionResolutionVisitor, expr: &hir::Expr) {
debug!("resolve_expr(expr.id={:?})", expr.id);
let expr_extent = visitor.new_node_extent_with_dtor(expr.id);
let prev_cx = visitor.cx;
visitor.cx.parent = expr_extent;
{
let terminating_scopes = &mut visitor.terminating_scopes;
let mut terminating = |id: ast::NodeId| {
terminating_scopes.insert(id);
};
match expr.node {
// Conditional or repeating scopes are always terminating
// scopes, meaning that temporaries cannot outlive them.
// This ensures fixed size stacks.
hir::ExprBinary(codemap::Spanned { node: hir::BiAnd, .. }, _, ref r) |
hir::ExprBinary(codemap::Spanned { node: hir::BiOr, .. }, _, ref r) => {
// For shortcircuiting operators, mark the RHS as a terminating
// scope since it only executes conditionally.
terminating(r.id);
}
hir::ExprIf(_, ref then, Some(ref otherwise)) => {
terminating(then.id);
terminating(otherwise.id);
}
hir::ExprIf(ref expr, ref then, None) => {
terminating(expr.id);
terminating(then.id);
}
hir::ExprLoop(ref body, _) => {
terminating(body.id);
}
hir::ExprWhile(ref expr, ref body, _) => {
terminating(expr.id);
terminating(body.id);
}
hir::ExprMatch(..) => {
visitor.cx.var_parent = expr_extent;
}
hir::ExprAssignOp(..) | hir::ExprIndex(..) |
hir::ExprUnary(..) | hir::ExprCall(..) | hir::ExprMethodCall(..) => {
// FIXME(#6268) Nested method calls
//
// The lifetimes for a call or method call look as follows:
//
// call.id
// - arg0.id
// - ...
// - argN.id
// - call.callee_id
//
// The idea is that call.callee_id represents *the time when
// the invoked function is actually running* and call.id
// represents *the time to prepare the arguments and make the
// call*. See the section "Borrows in Calls" borrowck/README.md
// for an extended explanation of why this distinction is
// important.
//
// record_superlifetime(new_cx, expr.callee_id);
}
_ => {}
}
}
intravisit::walk_expr(visitor, expr);
visitor.cx = prev_cx;
}
fn resolve_local(visitor: &mut RegionResolutionVisitor, local: &hir::Local) {
debug!("resolve_local(local.id={:?},local.init={:?})",
local.id,local.init.is_some());
// For convenience in trans, associate with the local-id the var
// scope that will be used for any bindings declared in this
// pattern.
let blk_scope = visitor.cx.var_parent;
assert!(blk_scope != ROOT_CODE_EXTENT); // locals must be within a block
visitor.region_maps.record_var_scope(local.id, blk_scope);
// As an exception to the normal rules governing temporary
// lifetimes, initializers in a let have a temporary lifetime
// of the enclosing block. This means that e.g. a program
// like the following is legal:
//
// let ref x = HashMap::new();
//
// Because the hash map will be freed in the enclosing block.
//
// We express the rules more formally based on 3 grammars (defined
// fully in the helpers below that implement them):
//
// 1. `E&`, which matches expressions like `&<rvalue>` that
// own a pointer into the stack.
//
// 2. `P&`, which matches patterns like `ref x` or `(ref x, ref
// y)` that produce ref bindings into the value they are
// matched against or something (at least partially) owned by
// the value they are matched against. (By partially owned,
// I mean that creating a binding into a ref-counted or managed value
// would still count.)
//
// 3. `ET`, which matches both rvalues like `foo()` as well as lvalues
// based on rvalues like `foo().x[2].y`.
//
// A subexpression `<rvalue>` that appears in a let initializer
// `let pat [: ty] = expr` has an extended temporary lifetime if
// any of the following conditions are met:
//
// A. `pat` matches `P&` and `expr` matches `ET`
// (covers cases where `pat` creates ref bindings into an rvalue
// produced by `expr`)
// B. `ty` is a borrowed pointer and `expr` matches `ET`
// (covers cases where coercion creates a borrow)
// C. `expr` matches `E&`
// (covers cases `expr` borrows an rvalue that is then assigned
// to memory (at least partially) owned by the binding)
//
// Here are some examples hopefully giving an intuition where each
// rule comes into play and why:
//
// Rule A. `let (ref x, ref y) = (foo().x, 44)`. The rvalue `(22, 44)`
// would have an extended lifetime, but not `foo()`.
//
// Rule B. `let x: &[...] = [foo().x]`. The rvalue `[foo().x]`
// would have an extended lifetime, but not `foo()`.
//
// Rule C. `let x = &foo().x`. The rvalue ``foo()` would have extended
// lifetime.
//
// In some cases, multiple rules may apply (though not to the same
// rvalue). For example:
//
// let ref x = [&a(), &b()];
//
// Here, the expression `[...]` has an extended lifetime due to rule
// A, but the inner rvalues `a()` and `b()` have an extended lifetime
// due to rule C.
//
// FIXME(#6308) -- Note that `[]` patterns work more smoothly post-DST.
match local.init {
Some(ref expr) => {
record_rvalue_scope_if_borrow_expr(visitor, &expr, blk_scope);
let is_borrow =
if let Some(ref ty) = local.ty { is_borrowed_ty(&ty) } else { false };
if is_binding_pat(&local.pat) || is_borrow {
record_rvalue_scope(visitor, &expr, blk_scope);
}
}
None => { }
}
intravisit::walk_local(visitor, local);
/// True if `pat` match the `P&` nonterminal:
///
/// P& = ref X
/// | StructName { ..., P&, ... }
/// | VariantName(..., P&, ...)
/// | [ ..., P&, ... ]
/// | ( ..., P&, ... )
/// | box P&
fn is_binding_pat(pat: &hir::Pat) -> bool {
match pat.node {
PatKind::Ident(hir::BindByRef(_), _, _) => true,
PatKind::Struct(_, ref field_pats, _) => {
field_pats.iter().any(|fp| is_binding_pat(&fp.node.pat))
}
PatKind::Vec(ref pats1, ref pats2, ref pats3) => {
pats1.iter().any(|p| is_binding_pat(&p)) ||
pats2.iter().any(|p| is_binding_pat(&p)) ||
pats3.iter().any(|p| is_binding_pat(&p))
}
PatKind::TupleStruct(_, Some(ref subpats)) |
PatKind::Tup(ref subpats) => {
subpats.iter().any(|p| is_binding_pat(&p))
}
PatKind::Box(ref subpat) => {
is_binding_pat(&subpat)
}
_ => false,
}
}
/// True if `ty` is a borrowed pointer type like `&int` or `&[...]`.
fn is_borrowed_ty(ty: &hir::Ty) -> bool {
match ty.node {
hir::TyRptr(..) => true,
_ => false
}
}
/// If `expr` matches the `E&` grammar, then records an extended rvalue scope as appropriate:
///
/// E& = & ET
/// | StructName { ..., f: E&, ... }
/// | [ ..., E&, ... ]
/// | ( ..., E&, ... )
/// | {...; E&}
/// | box E&
/// | E& as ...
/// | ( E& )
fn record_rvalue_scope_if_borrow_expr(visitor: &mut RegionResolutionVisitor,
expr: &hir::Expr,
blk_id: CodeExtent) {
match expr.node {
hir::ExprAddrOf(_, ref subexpr) => {
record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id);
record_rvalue_scope(visitor, &subexpr, blk_id);
}
hir::ExprStruct(_, ref fields, _) => {
for field in fields {
record_rvalue_scope_if_borrow_expr(
visitor, &field.expr, blk_id);
}
}
hir::ExprVec(ref subexprs) |
hir::ExprTup(ref subexprs) => {
for subexpr in subexprs {
record_rvalue_scope_if_borrow_expr(
visitor, &subexpr, blk_id);
}
}
hir::ExprCast(ref subexpr, _) => {
record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id)
}
hir::ExprBlock(ref block) => {
match block.expr {
Some(ref subexpr) => {
record_rvalue_scope_if_borrow_expr(
visitor, &subexpr, blk_id);
}
None => { }
}
}
_ => {
}
}
}
/// Applied to an expression `expr` if `expr` -- or something owned or partially owned by
/// `expr` -- is going to be indirectly referenced by a variable in a let statement. In that
/// case, the "temporary lifetime" or `expr` is extended to be the block enclosing the `let`
/// statement.
///
/// More formally, if `expr` matches the grammar `ET`, record the rvalue scope of the matching
/// `<rvalue>` as `blk_id`:
///
/// ET = *ET
/// | ET[...]
/// | ET.f
/// | (ET)
/// | <rvalue>
///
/// Note: ET is intended to match "rvalues or lvalues based on rvalues".
fn record_rvalue_scope<'a>(visitor: &mut RegionResolutionVisitor,
expr: &'a hir::Expr,
blk_scope: CodeExtent) {
let mut expr = expr;
loop {
// Note: give all the expressions matching `ET` with the
// extended temporary lifetime, not just the innermost rvalue,
// because in trans if we must compile e.g. `*rvalue()`
// into a temporary, we request the temporary scope of the
// outer expression.
visitor.region_maps.record_rvalue_scope(expr.id, blk_scope);
match expr.node {
hir::ExprAddrOf(_, ref subexpr) |
hir::ExprUnary(hir::UnDeref, ref subexpr) |
hir::ExprField(ref subexpr, _) |
hir::ExprTupField(ref subexpr, _) |
hir::ExprIndex(ref subexpr, _) => {
expr = &subexpr;
}
_ => {
return;
}
}
}
}
}
fn resolve_item(visitor: &mut RegionResolutionVisitor, item: &hir::Item) {
// Items create a new outer block scope as far as we're concerned.
let prev_cx = visitor.cx;
let prev_ts = mem::replace(&mut visitor.terminating_scopes, NodeSet());
visitor.cx = Context {
root_id: None,
var_parent: ROOT_CODE_EXTENT,
parent: ROOT_CODE_EXTENT
};
intravisit::walk_item(visitor, item);
visitor.create_item_scope_if_needed(item.id);
visitor.cx = prev_cx;
visitor.terminating_scopes = prev_ts;
}
fn resolve_fn(visitor: &mut RegionResolutionVisitor,
kind: FnKind,
decl: &hir::FnDecl,
body: &hir::Block,
sp: Span,
id: ast::NodeId) {
debug!("region::resolve_fn(id={:?}, \
span={:?}, \
body.id={:?}, \
cx.parent={:?})",
id,
visitor.sess.codemap().span_to_string(sp),
body.id,
visitor.cx.parent);
visitor.cx.parent = visitor.new_code_extent(
CodeExtentData::CallSiteScope { fn_id: id, body_id: body.id });
let fn_decl_scope = visitor.new_code_extent(
CodeExtentData::ParameterScope { fn_id: id, body_id: body.id });
if let Some(root_id) = visitor.cx.root_id {
visitor.region_maps.record_fn_parent(body.id, root_id);
}
let outer_cx = visitor.cx;
let outer_ts = mem::replace(&mut visitor.terminating_scopes, NodeSet());
visitor.terminating_scopes.insert(body.id);
// The arguments and `self` are parented to the fn.
visitor.cx = Context {
root_id: Some(body.id),
parent: ROOT_CODE_EXTENT,
var_parent: fn_decl_scope,
};
intravisit::walk_fn_decl(visitor, decl);
intravisit::walk_fn_kind(visitor, kind);
// The body of the every fn is a root scope.
visitor.cx = Context {
root_id: Some(body.id),
parent: fn_decl_scope,
var_parent: fn_decl_scope
};
visitor.visit_block(body);
// Restore context we had at the start.
visitor.cx = outer_cx;
visitor.terminating_scopes = outer_ts;
}
impl<'a> RegionResolutionVisitor<'a> {
/// Records the current parent (if any) as the parent of `child_scope`.
fn new_code_extent(&mut self, child_scope: CodeExtentData) -> CodeExtent {
self.region_maps.intern_code_extent(child_scope, self.cx.parent)
}
fn new_node_extent(&mut self, child_scope: ast::NodeId) -> CodeExtent {
self.new_code_extent(CodeExtentData::Misc(child_scope))
}
fn new_node_extent_with_dtor(&mut self, id: ast::NodeId) -> CodeExtent {
// If node was previously marked as a terminating scope during the
// recursive visit of its parent node in the AST, then we need to
// account for the destruction scope representing the extent of
// the destructors that run immediately after it completes.
if self.terminating_scopes.contains(&id) {
let ds = self.new_code_extent(
CodeExtentData::DestructionScope(id));
self.region_maps.intern_node(id, ds)
} else {
self.new_node_extent(id)
}
}
fn create_item_scope_if_needed(&mut self, id: ast::NodeId) {
// create a region for the destruction scope - this is needed
// for constructing parameter environments based on the item.
// functions put their destruction scopes *inside* their parameter
// scopes.
let scope = CodeExtentData::DestructionScope(id);
if !self.region_maps.code_extent_interner.borrow().contains_key(&scope) {
self.region_maps.intern_code_extent(scope, ROOT_CODE_EXTENT);
}
}
}
impl<'a, 'v> Visitor<'v> for RegionResolutionVisitor<'a> {
fn visit_block(&mut self, b: &Block) {
resolve_block(self, b);
}
fn visit_item(&mut self, i: &Item) {
resolve_item(self, i);
}
fn visit_impl_item(&mut self, ii: &hir::ImplItem) {
intravisit::walk_impl_item(self, ii);
self.create_item_scope_if_needed(ii.id);
}
fn visit_trait_item(&mut self, ti: &hir::TraitItem) {
intravisit::walk_trait_item(self, ti);
self.create_item_scope_if_needed(ti.id);
}
fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v FnDecl,
b: &'v Block, s: Span, n: NodeId) {
resolve_fn(self, fk, fd, b, s, n);
}
fn visit_arm(&mut self, a: &Arm) {
resolve_arm(self, a);
}
fn visit_pat(&mut self, p: &Pat) {
resolve_pat(self, p);
}
fn visit_stmt(&mut self, s: &Stmt) {
resolve_stmt(self, s);
}
fn visit_expr(&mut self, ex: &Expr) {
resolve_expr(self, ex);
}
fn visit_local(&mut self, l: &Local) {
resolve_local(self, l);
}
}
pub fn resolve_crate(sess: &Session, map: &ast_map::Map) -> RegionMaps {
let _task = map.dep_graph.in_task(DepNode::RegionResolveCrate);
let krate = map.krate();
let maps = RegionMaps {
code_extents: RefCell::new(vec![]),
code_extent_interner: RefCell::new(FnvHashMap()),
scope_map: RefCell::new(vec![]),
var_map: RefCell::new(NodeMap()),
rvalue_scopes: RefCell::new(NodeMap()),
fn_tree: RefCell::new(NodeMap()),
};
let root_extent = maps.bogus_code_extent(
CodeExtentData::DestructionScope(ast::DUMMY_NODE_ID));
assert_eq!(root_extent, ROOT_CODE_EXTENT);
let bogus_extent = maps.bogus_code_extent(
CodeExtentData::Misc(ast::DUMMY_NODE_ID));
assert_eq!(bogus_extent, DUMMY_CODE_EXTENT);
{
let mut visitor = RegionResolutionVisitor {
sess: sess,
region_maps: &maps,
cx: Context {
root_id: None,
parent: ROOT_CODE_EXTENT,
var_parent: ROOT_CODE_EXTENT
},
terminating_scopes: NodeSet()
};
krate.visit_all_items(&mut visitor);
}
return maps;
}
pub fn resolve_inlined_item(sess: &Session,
region_maps: &RegionMaps,
item: &InlinedItem) {
let mut visitor = RegionResolutionVisitor {
sess: sess,
region_maps: region_maps,
cx: Context {
root_id: None,
parent: ROOT_CODE_EXTENT,
var_parent: ROOT_CODE_EXTENT
},
terminating_scopes: NodeSet()
};
item.visit(&mut visitor);
}
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