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Rollup merge of #64500 - nnethercote:ObligForest-fixups, r=nikomatsakis

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Various `ObligationForest` improvements

These commits make the code both nicer and faster.

r? @nikomatsakis
This commit is contained in:
Mazdak Farrokhzad 2019-09-17 03:08:38 +02:00 committed by GitHub
commit 1e3b57ee77
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GPG key ID: 4AEE18F83AFDEB23
4 changed files with 148 additions and 167 deletions
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2
src/librustc_data_structures/indexed_vec.rs
View file

@ -149,7 +149,7 @@ macro_rules! newtype_index {
#[inline]
$v const unsafe fn from_u32_unchecked(value: u32) -> Self {
unsafe { $type { private: value } }
$type { private: value }
}
/// Extracts the value of this index as an integer.

6
src/librustc_data_structures/obligation_forest/graphviz.rs
View file

@ -74,9 +74,9 @@ impl<'a, O: ForestObligation + 'a> dot::GraphWalk<'a> for &'a ObligationForest<O
.flat_map(|i| {
let node = &self.nodes[i];
node.parent.iter().map(|p| p.get())
.chain(node.dependents.iter().map(|p| p.get()))
.map(move |p| (p, i))
node.parent.iter()
.chain(node.dependents.iter())
.map(move |p| (p.index(), i))
})
.collect()
}

287
src/librustc_data_structures/obligation_forest/mod.rs
View file

@ -9,7 +9,7 @@
//! `ObligationForest` supports two main public operations (there are a
//! few others not discussed here):
//!
//! 1. Add a new root obligations (`push_tree`).
//! 1. Add a new root obligations (`register_obligation`).
//! 2. Process the pending obligations (`process_obligations`).
//!
//! When a new obligation `N` is added, it becomes the root of an
@ -20,13 +20,13 @@
//! with every pending obligation (so that will include `N`, the first
//! time). The callback also receives a (mutable) reference to the
//! per-tree state `T`. The callback should process the obligation `O`
//! that it is given and return one of three results:
//! that it is given and return a `ProcessResult`:
//!
//! - `Ok(None)` -> ambiguous result. Obligation was neither a success
//! - `Unchanged` -> ambiguous result. Obligation was neither a success
//! nor a failure. It is assumed that further attempts to process the
//! obligation will yield the same result unless something in the
//! surrounding environment changes.
//! - `Ok(Some(C))` - the obligation was *shallowly successful*. The
//! - `Changed(C)` - the obligation was *shallowly successful*. The
//! vector `C` is a list of subobligations. The meaning of this is that
//! `O` was successful on the assumption that all the obligations in `C`
//! are also successful. Therefore, `O` is only considered a "true"
@ -34,7 +34,7 @@
//! state and the obligations in `C` become the new pending
//! obligations. They will be processed the next time you call
//! `process_obligations`.
//! - `Err(E)` -> obligation failed with error `E`. We will collect this
//! - `Error(E)` -> obligation failed with error `E`. We will collect this
//! error and return it from `process_obligations`, along with the
//! "backtrace" of obligations (that is, the list of obligations up to
//! and including the root of the failed obligation). No further
@ -47,55 +47,50 @@
//! - `completed`: a list of obligations where processing was fully
//! completed without error (meaning that all transitive subobligations
//! have also been completed). So, for example, if the callback from
//! `process_obligations` returns `Ok(Some(C))` for some obligation `O`,
//! `process_obligations` returns `Changed(C)` for some obligation `O`,
//! then `O` will be considered completed right away if `C` is the
//! empty vector. Otherwise it will only be considered completed once
//! all the obligations in `C` have been found completed.
//! - `errors`: a list of errors that occurred and associated backtraces
//! at the time of error, which can be used to give context to the user.
//! - `stalled`: if true, then none of the existing obligations were
//! *shallowly successful* (that is, no callback returned `Ok(Some(_))`).
//! *shallowly successful* (that is, no callback returned `Changed(_)`).
//! This implies that all obligations were either errors or returned an
//! ambiguous result, which means that any further calls to
//! `process_obligations` would simply yield back further ambiguous
//! results. This is used by the `FulfillmentContext` to decide when it
//! has reached a steady state.
//!
//! #### Snapshots
//!
//! The `ObligationForest` supports a limited form of snapshots; see
//! `start_snapshot`, `commit_snapshot`, and `rollback_snapshot`. In
//! particular, you can use a snapshot to roll back new root
//! obligations. However, it is an error to attempt to
//! `process_obligations` during a snapshot.
//!
//! ### Implementation details
//!
//! For the most part, comments specific to the implementation are in the
//! code. This file only contains a very high-level overview. Basically,
//! the forest is stored in a vector. Each element of the vector is a node
//! in some tree. Each node in the vector has the index of an (optional)
//! parent and (for convenience) its root (which may be itself). It also
//! has a current state, described by `NodeState`. After each
//! processing step, we compress the vector to remove completed and error
//! nodes, which aren't needed anymore.
//! in some tree. Each node in the vector has the index of its dependents,
//! including the first dependent which is known as the parent. It also
//! has a current state, described by `NodeState`. After each processing
//! step, we compress the vector to remove completed and error nodes, which
//! aren't needed anymore.
use crate::fx::{FxHashMap, FxHashSet};
use crate::indexed_vec::Idx;
use crate::newtype_index;
use std::cell::Cell;
use std::cell::{Cell, RefCell};
use std::collections::hash_map::Entry;
use std::fmt::Debug;
use std::hash;
use std::marker::PhantomData;
mod node_index;
use self::node_index::NodeIndex;
mod graphviz;
#[cfg(test)]
mod tests;
newtype_index! {
pub struct NodeIndex { .. }
}
pub trait ForestObligation : Clone + Debug {
type Predicate : Clone + hash::Hash + Eq + Debug;
@ -148,18 +143,22 @@ pub struct ObligationForest<O: ForestObligation> {
/// At the end of processing, those nodes will be removed by a
/// call to `compress`.
///
/// At all times we maintain the invariant that every node appears
/// at a higher index than its parent. This is needed by the
/// backtrace iterator (which uses `split_at`).
/// Ideally, this would be an `IndexVec<NodeIndex, Node<O>>`. But that is
/// slower, because this vector is accessed so often that the
/// `u32`-to-`usize` conversions required for accesses are significant.
nodes: Vec<Node<O>>,
/// A cache of predicates that have been successfully completed.
done_cache: FxHashSet<O::Predicate>,
/// An cache of the nodes in `nodes`, indexed by predicate.
/// A cache of the nodes in `nodes`, indexed by predicate. Unfortunately,
/// its contents are not guaranteed to match those of `nodes`. See the
/// comments in `process_obligation` for details.
waiting_cache: FxHashMap<O::Predicate, NodeIndex>,
scratch: Option<Vec<usize>>,
/// A scratch vector reused in various operations, to avoid allocating new
/// vectors.
scratch: RefCell<Vec<usize>>,
obligation_tree_id_generator: ObligationTreeIdGenerator,
@ -178,19 +177,41 @@ struct Node<O> {
obligation: O,
state: Cell<NodeState>,
/// The parent of a node - the original obligation of
/// which it is a subobligation. Except for error reporting,
/// it is just like any member of `dependents`.
/// The parent of a node - the original obligation of which it is a
/// subobligation. Except for error reporting, it is just like any member
/// of `dependents`.
///
/// Unlike `ObligationForest::nodes`, this uses `NodeIndex` rather than
/// `usize` for the index, because keeping the size down is more important
/// than the cost of converting to a `usize` for indexing.
parent: Option<NodeIndex>,
/// Obligations that depend on this obligation for their
/// completion. They must all be in a non-pending state.
/// Obligations that depend on this obligation for their completion. They
/// must all be in a non-pending state.
///
/// This uses `NodeIndex` for the same reason as `parent`.
dependents: Vec<NodeIndex>,
/// Identifier of the obligation tree to which this node belongs.
obligation_tree_id: ObligationTreeId,
}
impl<O> Node<O> {
fn new(
parent: Option<NodeIndex>,
obligation: O,
obligation_tree_id: ObligationTreeId
) -> Node<O> {
Node {
obligation,
state: Cell::new(NodeState::Pending),
parent,
dependents: vec![],
obligation_tree_id,
}
}
}
/// The state of one node in some tree within the forest. This
/// represents the current state of processing for the obligation (of
/// type `O`) associated with this node.
@ -262,7 +283,7 @@ impl<O: ForestObligation> ObligationForest<O> {
nodes: vec![],
done_cache: Default::default(),
waiting_cache: Default::default(),
scratch: Some(vec![]),
scratch: RefCell::new(vec![]),
obligation_tree_id_generator: (0..).map(ObligationTreeId),
error_cache: Default::default(),
}
@ -275,14 +296,12 @@ impl<O: ForestObligation> ObligationForest<O> {
}
/// Registers an obligation.
///
/// This CAN be done in a snapshot
pub fn register_obligation(&mut self, obligation: O) {
// Ignore errors here - there is no guarantee of success.
let _ = self.register_obligation_at(obligation, None);
}
// returns Err(()) if we already know this obligation failed.
// Returns Err(()) if we already know this obligation failed.
fn register_obligation_at(&mut self, obligation: O, parent: Option<NodeIndex>)
-> Result<(), ()>
{
@ -294,15 +313,16 @@ impl<O: ForestObligation> ObligationForest<O> {
Entry::Occupied(o) => {
debug!("register_obligation_at({:?}, {:?}) - duplicate of {:?}!",
obligation, parent, o.get());
let node = &mut self.nodes[o.get().get()];
if let Some(parent) = parent {
let node = &mut self.nodes[o.get().index()];
if let Some(parent_index) = parent {
// If the node is already in `waiting_cache`, it's already
// been marked with a parent. (It's possible that parent
// has been cleared by `apply_rewrites`, though.) So just
// dump `parent` into `node.dependents`... unless it's
// already in `node.dependents` or `node.parent`.
if !node.dependents.contains(&parent) && Some(parent) != node.parent {
node.dependents.push(parent);
if !node.dependents.contains(&parent_index) &&
Some(parent_index) != node.parent {
node.dependents.push(parent_index);
}
}
if let NodeState::Error = node.state.get() {
@ -316,9 +336,8 @@ impl<O: ForestObligation> ObligationForest<O> {
obligation, parent, self.nodes.len());
let obligation_tree_id = match parent {
Some(p) => {
let parent_node = &self.nodes[p.get()];
parent_node.obligation_tree_id
Some(parent_index) => {
self.nodes[parent_index.index()].obligation_tree_id
}
None => self.obligation_tree_id_generator.next().unwrap()
};
@ -342,13 +361,11 @@ impl<O: ForestObligation> ObligationForest<O> {
}
/// Converts all remaining obligations to the given error.
///
/// This cannot be done during a snapshot.
pub fn to_errors<E: Clone>(&mut self, error: E) -> Vec<Error<O, E>> {
let mut errors = vec![];
for index in 0..self.nodes.len() {
if let NodeState::Pending = self.nodes[index].state.get() {
let backtrace = self.error_at(index);
for (i, node) in self.nodes.iter().enumerate() {
if let NodeState::Pending = node.state.get() {
let backtrace = self.error_at(i);
errors.push(Error {
error: error.clone(),
backtrace,
@ -373,7 +390,6 @@ impl<O: ForestObligation> ObligationForest<O> {
fn insert_into_error_cache(&mut self, node_index: usize) {
let node = &self.nodes[node_index];
self.error_cache
.entry(node.obligation_tree_id)
.or_default()
@ -393,16 +409,22 @@ impl<O: ForestObligation> ObligationForest<O> {
let mut errors = vec![];
let mut stalled = true;
for index in 0..self.nodes.len() {
debug!("process_obligations: node {} == {:?}", index, self.nodes[index]);
for i in 0..self.nodes.len() {
let node = &mut self.nodes[i];
let result = match self.nodes[index] {
Node { ref state, ref mut obligation, .. } if state.get() == NodeState::Pending =>
processor.process_obligation(obligation),
debug!("process_obligations: node {} == {:?}", i, node);
// `processor.process_obligation` can modify the predicate within
// `node.obligation`, and that predicate is the key used for
// `self.waiting_cache`. This means that `self.waiting_cache` can
// get out of sync with `nodes`. It's not very common, but it does
// happen, and code in `compress` has to allow for it.
let result = match node.state.get() {
NodeState::Pending => processor.process_obligation(&mut node.obligation),
_ => continue
};
debug!("process_obligations: node {} got result {:?}", index, result);
debug!("process_obligations: node {} got result {:?}", i, result);
match result {
ProcessResult::Unchanged => {
@ -411,23 +433,23 @@ impl<O: ForestObligation> ObligationForest<O> {
ProcessResult::Changed(children) => {
// We are not (yet) stalled.
stalled = false;
self.nodes[index].state.set(NodeState::Success);
node.state.set(NodeState::Success);
for child in children {
let st = self.register_obligation_at(
child,
Some(NodeIndex::new(index))
Some(NodeIndex::new(i))
);
if let Err(()) = st {
// error already reported - propagate it
// Error already reported - propagate it
// to our node.
self.error_at(index);
self.error_at(i);
}
}
}
ProcessResult::Error(err) => {
stalled = false;
let backtrace = self.error_at(index);
let backtrace = self.error_at(i);
errors.push(Error {
error: err,
backtrace,
@ -448,8 +470,6 @@ impl<O: ForestObligation> ObligationForest<O> {
self.mark_as_waiting();
self.process_cycles(processor);
// Now we have to compress the result
let completed = self.compress(do_completed);
debug!("process_obligations: complete");
@ -465,97 +485,92 @@ impl<O: ForestObligation> ObligationForest<O> {
/// report all cycles between them. This should be called
/// after `mark_as_waiting` marks all nodes with pending
/// subobligations as NodeState::Waiting.
fn process_cycles<P>(&mut self, processor: &mut P)
fn process_cycles<P>(&self, processor: &mut P)
where P: ObligationProcessor<Obligation=O>
{
let mut stack = self.scratch.take().unwrap();
let mut stack = self.scratch.replace(vec![]);
debug_assert!(stack.is_empty());
debug!("process_cycles()");
for index in 0..self.nodes.len() {
for (i, node) in self.nodes.iter().enumerate() {
// For rustc-benchmarks/inflate-0.1.0 this state test is extremely
// hot and the state is almost always `Pending` or `Waiting`. It's
// a win to handle the no-op cases immediately to avoid the cost of
// the function call.
let state = self.nodes[index].state.get();
match state {
match node.state.get() {
NodeState::Waiting | NodeState::Pending | NodeState::Done | NodeState::Error => {},
_ => self.find_cycles_from_node(&mut stack, processor, index),
_ => self.find_cycles_from_node(&mut stack, processor, i),
}
}
debug!("process_cycles: complete");
debug_assert!(stack.is_empty());
self.scratch = Some(stack);
self.scratch.replace(stack);
}
fn find_cycles_from_node<P>(&self, stack: &mut Vec<usize>,
processor: &mut P, index: usize)
fn find_cycles_from_node<P>(&self, stack: &mut Vec<usize>, processor: &mut P, i: usize)
where P: ObligationProcessor<Obligation=O>
{
let node = &self.nodes[index];
let state = node.state.get();
match state {
let node = &self.nodes[i];
match node.state.get() {
NodeState::OnDfsStack => {
let index =
stack.iter().rposition(|n| *n == index).unwrap();
processor.process_backedge(stack[index..].iter().map(GetObligation(&self.nodes)),
let i = stack.iter().rposition(|n| *n == i).unwrap();
processor.process_backedge(stack[i..].iter().map(GetObligation(&self.nodes)),
PhantomData);
}
NodeState::Success => {
node.state.set(NodeState::OnDfsStack);
stack.push(index);
for dependent in node.parent.iter().chain(node.dependents.iter()) {
self.find_cycles_from_node(stack, processor, dependent.get());
stack.push(i);
for index in node.parent.iter().chain(node.dependents.iter()) {
self.find_cycles_from_node(stack, processor, index.index());
}
stack.pop();
node.state.set(NodeState::Done);
},
NodeState::Waiting | NodeState::Pending => {
// this node is still reachable from some pending node. We
// This node is still reachable from some pending node. We
// will get to it when they are all processed.
}
NodeState::Done | NodeState::Error => {
// already processed that node
// Already processed that node.
}
};
}
/// Returns a vector of obligations for `p` and all of its
/// ancestors, putting them into the error state in the process.
fn error_at(&mut self, p: usize) -> Vec<O> {
let mut error_stack = self.scratch.take().unwrap();
fn error_at(&self, mut i: usize) -> Vec<O> {
let mut error_stack = self.scratch.replace(vec![]);
let mut trace = vec![];
let mut n = p;
loop {
self.nodes[n].state.set(NodeState::Error);
trace.push(self.nodes[n].obligation.clone());
error_stack.extend(self.nodes[n].dependents.iter().map(|x| x.get()));
let node = &self.nodes[i];
node.state.set(NodeState::Error);
trace.push(node.obligation.clone());
error_stack.extend(node.dependents.iter().map(|index| index.index()));
// loop to the parent
match self.nodes[n].parent {
Some(q) => n = q.get(),
// Loop to the parent.
match node.parent {
Some(parent_index) => i = parent_index.index(),
None => break
}
}
while let Some(i) = error_stack.pop() {
match self.nodes[i].state.get() {
let node = &self.nodes[i];
match node.state.get() {
NodeState::Error => continue,
_ => self.nodes[i].state.set(NodeState::Error),
_ => node.state.set(NodeState::Error),
}
let node = &self.nodes[i];
error_stack.extend(
node.parent.iter().chain(node.dependents.iter()).map(|x| x.get())
node.parent.iter().chain(node.dependents.iter()).map(|index| index.index())
);
}
self.scratch = Some(error_stack);
self.scratch.replace(error_stack);
trace
}
@ -563,7 +578,7 @@ impl<O: ForestObligation> ObligationForest<O> {
#[inline(always)]
fn inlined_mark_neighbors_as_waiting_from(&self, node: &Node<O>) {
for dependent in node.parent.iter().chain(node.dependents.iter()) {
self.mark_as_waiting_from(&self.nodes[dependent.get()]);
self.mark_as_waiting_from(&self.nodes[dependent.index()]);
}
}
@ -609,7 +624,7 @@ impl<O: ForestObligation> ObligationForest<O> {
#[inline(never)]
fn compress(&mut self, do_completed: DoCompleted) -> Option<Vec<O>> {
let nodes_len = self.nodes.len();
let mut node_rewrites: Vec<_> = self.scratch.take().unwrap();
let mut node_rewrites: Vec<_> = self.scratch.replace(vec![]);
node_rewrites.extend(0..nodes_len);
let mut dead_nodes = 0;
@ -620,7 +635,8 @@ impl<O: ForestObligation> ObligationForest<O> {
// self.nodes[i - dead_nodes..i] are all dead
// self.nodes[i..] are unchanged
for i in 0..self.nodes.len() {
match self.nodes[i].state.get() {
let node = &self.nodes[i];
match node.state.get() {
NodeState::Pending | NodeState::Waiting => {
if dead_nodes > 0 {
self.nodes.swap(i, i - dead_nodes);
@ -628,13 +644,16 @@ impl<O: ForestObligation> ObligationForest<O> {
}
}
NodeState::Done => {
// Avoid cloning the key (predicate) in case it exists in the waiting cache
// This lookup can fail because the contents of
// `self.waiting_cache` is not guaranteed to match those of
// `self.nodes`. See the comment in `process_obligation`
// for more details.
if let Some((predicate, _)) = self.waiting_cache
.remove_entry(self.nodes[i].obligation.as_predicate())
.remove_entry(node.obligation.as_predicate())
{
self.done_cache.insert(predicate);
} else {
self.done_cache.insert(self.nodes[i].obligation.as_predicate().clone());
self.done_cache.insert(node.obligation.as_predicate().clone());
}
node_rewrites[i] = nodes_len;
dead_nodes += 1;
@ -643,7 +662,7 @@ impl<O: ForestObligation> ObligationForest<O> {
// We *intentionally* remove the node from the cache at this point. Otherwise
// tests must come up with a different type on every type error they
// check against.
self.waiting_cache.remove(self.nodes[i].obligation.as_predicate());
self.waiting_cache.remove(node.obligation.as_predicate());
node_rewrites[i] = nodes_len;
dead_nodes += 1;
self.insert_into_error_cache(i);
@ -655,12 +674,11 @@ impl<O: ForestObligation> ObligationForest<O> {
// No compression needed.
if dead_nodes == 0 {
node_rewrites.truncate(0);
self.scratch = Some(node_rewrites);
self.scratch.replace(node_rewrites);
return if do_completed == DoCompleted::Yes { Some(vec![]) } else { None };
}
// Pop off all the nodes we killed and extract the success
// stories.
// Pop off all the nodes we killed and extract the success stories.
let successful = if do_completed == DoCompleted::Yes {
Some((0..dead_nodes)
.map(|_| self.nodes.pop().unwrap())
@ -679,7 +697,7 @@ impl<O: ForestObligation> ObligationForest<O> {
self.apply_rewrites(&node_rewrites);
node_rewrites.truncate(0);
self.scratch = Some(node_rewrites);
self.scratch.replace(node_rewrites);
successful
}
@ -689,58 +707,41 @@ impl<O: ForestObligation> ObligationForest<O> {
for node in &mut self.nodes {
if let Some(index) = node.parent {
let new_index = node_rewrites[index.get()];
if new_index >= nodes_len {
// parent dead due to error
let new_i = node_rewrites[index.index()];
if new_i >= nodes_len {
node.parent = None;
} else {
node.parent = Some(NodeIndex::new(new_index));
node.parent = Some(NodeIndex::new(new_i));
}
}
let mut i = 0;
while i < node.dependents.len() {
let new_index = node_rewrites[node.dependents[i].get()];
if new_index >= nodes_len {
let new_i = node_rewrites[node.dependents[i].index()];
if new_i >= nodes_len {
node.dependents.swap_remove(i);
} else {
node.dependents[i] = NodeIndex::new(new_index);
node.dependents[i] = NodeIndex::new(new_i);
i += 1;
}
}
}
let mut kill_list = vec![];
for (predicate, index) in &mut self.waiting_cache {
let new_index = node_rewrites[index.get()];
if new_index >= nodes_len {
kill_list.push(predicate.clone());
// This updating of `self.waiting_cache` is necessary because the
// removal of nodes within `compress` can fail. See above.
self.waiting_cache.retain(|_predicate, index| {
let new_i = node_rewrites[index.index()];
if new_i >= nodes_len {
false
} else {
*index = NodeIndex::new(new_index);
*index = NodeIndex::new(new_i);
true
}
}
for predicate in kill_list { self.waiting_cache.remove(&predicate); }
});
}
}
impl<O> Node<O> {
fn new(
parent: Option<NodeIndex>,
obligation: O,
obligation_tree_id: ObligationTreeId
) -> Node<O> {
Node {
obligation,
state: Cell::new(NodeState::Pending),
parent,
dependents: vec![],
obligation_tree_id,
}
}
}
// I need a Clone closure
// I need a Clone closure.
#[derive(Clone)]
struct GetObligation<'a, O>(&'a [Node<O>]);

20
src/librustc_data_structures/obligation_forest/node_index.rs
View file

@ -1,20 +0,0 @@
use std::num::NonZeroU32;
use std::u32;
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub struct NodeIndex {
index: NonZeroU32,
}
impl NodeIndex {
#[inline]
pub fn new(value: usize) -> NodeIndex {
assert!(value < (u32::MAX as usize));
NodeIndex { index: NonZeroU32::new((value as u32) + 1).unwrap() }
}
#[inline]
pub fn get(self) -> usize {
(self.index.get() - 1) as usize
}
}