Remove `NodeState::{Waiting,Done}`.
`NodeState` has two states, `Success` and `Done`, that are only used within `ObligationForest` methods. This commit removes them, and renames the existing `Waiting` state as `Success`. We are left with three states: `Pending`, `Success`, and `Error`. `Success` is augmented with a new `WaitingState`, which indicates when (if ever) it was last waiting on one or more `Pending` nodes. This notion of "when" requires adding a "process generation" to `ObligationForest`; it is incremented on each call to `process_obligtions`. This commit is a performance win. - Most of the benefit comes from `mark_as_waiting` (which the commit renames as `mark_still_waiting_nodes`). This function used to do two things: (a) change all `Waiting` nodes to `Success`, and (b) mark all nodes that depend on a pending node as `Waiting`. In practice, many nodes went from `Waiting` to `Success` and then immediately back to `Waiting`. The use of generations lets us skip step (a). - A smaller benefit comes from not having to change nodes to the `Done` state in `process_cycles`.
This commit is contained in:
parent
e9469a6aec
commit
a8207b1958
|
@ -128,21 +128,19 @@ type ObligationTreeIdGenerator =
|
|||
::std::iter::Map<::std::ops::RangeFrom<usize>, fn(usize) -> ObligationTreeId>;
|
||||
|
||||
pub struct ObligationForest<O: ForestObligation> {
|
||||
/// The list of obligations. In between calls to
|
||||
/// `process_obligations`, this list only contains nodes in the
|
||||
/// `Pending` or `Success` state (with a non-zero number of
|
||||
/// incomplete children). During processing, some of those nodes
|
||||
/// may be changed to the error state, or we may find that they
|
||||
/// are completed (That is, `num_incomplete_children` drops to 0).
|
||||
/// At the end of processing, those nodes will be removed by a
|
||||
/// call to `compress`.
|
||||
/// The list of obligations. In between calls to `process_obligations`,
|
||||
/// this list only contains nodes in the `Pending` or `Success` state.
|
||||
///
|
||||
/// `usize` indices are used here and throughout this module, rather than
|
||||
/// `rustc_index::newtype_index!` indices, because this code is hot enough that the
|
||||
/// `u32`-to-`usize` conversions that would be required are significant,
|
||||
/// and space considerations are not important.
|
||||
/// `rustc_index::newtype_index!` indices, because this code is hot enough
|
||||
/// that the `u32`-to-`usize` conversions that would be required are
|
||||
/// significant, and space considerations are not important.
|
||||
nodes: Vec<Node<O>>,
|
||||
|
||||
/// The process generation is 1 on the first call to `process_obligations`,
|
||||
/// 2 on the second call, etc.
|
||||
gen: u32,
|
||||
|
||||
/// A cache of predicates that have been successfully completed.
|
||||
done_cache: FxHashSet<O::Predicate>,
|
||||
|
||||
|
@ -211,31 +209,61 @@ impl<O> Node<O> {
|
|||
/// represents the current state of processing for the obligation (of
|
||||
/// type `O`) associated with this node.
|
||||
///
|
||||
/// Outside of ObligationForest methods, nodes should be either Pending
|
||||
/// or Waiting.
|
||||
/// The non-`Error` state transitions are as follows.
|
||||
/// ```
|
||||
/// (Pre-creation)
|
||||
/// |
|
||||
/// | register_obligation_at() (called by process_obligations() and
|
||||
/// v from outside the crate)
|
||||
/// Pending
|
||||
/// |
|
||||
/// | process_obligations()
|
||||
/// v
|
||||
/// Success(not_waiting())
|
||||
/// | |
|
||||
/// | | mark_still_waiting_nodes()
|
||||
/// | v
|
||||
/// | Success(still_waiting())
|
||||
/// | |
|
||||
/// | | compress()
|
||||
/// v v
|
||||
/// (Removed)
|
||||
/// ```
|
||||
/// The `Error` state can be introduced in several places, via `error_at()`.
|
||||
///
|
||||
/// Outside of `ObligationForest` methods, nodes should be either `Pending` or
|
||||
/// `Success`.
|
||||
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
|
||||
enum NodeState {
|
||||
/// Obligations for which selection had not yet returned a
|
||||
/// non-ambiguous result.
|
||||
/// This obligation has not yet been selected successfully. Cannot have
|
||||
/// subobligations.
|
||||
Pending,
|
||||
|
||||
/// This obligation was selected successfully, but may or
|
||||
/// may not have subobligations.
|
||||
Success,
|
||||
/// This obligation was selected successfully, but it may be waiting on one
|
||||
/// or more pending subobligations, as indicated by the `WaitingState`.
|
||||
Success(WaitingState),
|
||||
|
||||
/// This obligation was selected successfully, but it has
|
||||
/// a pending subobligation.
|
||||
Waiting,
|
||||
|
||||
/// This obligation, along with its subobligations, are complete,
|
||||
/// and will be removed in the next collection.
|
||||
Done,
|
||||
|
||||
/// This obligation was resolved to an error. Error nodes are
|
||||
/// removed from the vector by the compression step.
|
||||
/// This obligation was resolved to an error. It will be removed by the
|
||||
/// next compression step.
|
||||
Error,
|
||||
}
|
||||
|
||||
/// Indicates when a `Success` node was last (if ever) waiting on one or more
|
||||
/// `Pending` nodes. The notion of "when" comes from `ObligationForest::gen`.
|
||||
/// - 0: "Not waiting". This is a special value, set by `process_obligation`,
|
||||
/// and usable because generation counting starts at 1.
|
||||
/// - 1..ObligationForest::gen: "Was waiting" in a previous generation, but
|
||||
/// waiting no longer. In other words, finished.
|
||||
/// - ObligationForest::gen: "Still waiting" in this generation.
|
||||
///
|
||||
/// Things to note about this encoding:
|
||||
/// - Every time `ObligationForest::gen` is incremented, all the "still
|
||||
/// waiting" nodes automatically become "was waiting".
|
||||
/// - `ObligationForest::is_still_waiting` is very cheap.
|
||||
///
|
||||
#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd)]
|
||||
struct WaitingState(u32);
|
||||
|
||||
#[derive(Debug)]
|
||||
pub struct Outcome<O, E> {
|
||||
/// Obligations that were completely evaluated, including all
|
||||
|
@ -272,6 +300,7 @@ impl<O: ForestObligation> ObligationForest<O> {
|
|||
pub fn new() -> ObligationForest<O> {
|
||||
ObligationForest {
|
||||
nodes: vec![],
|
||||
gen: 0,
|
||||
done_cache: Default::default(),
|
||||
active_cache: Default::default(),
|
||||
node_rewrites: RefCell::new(vec![]),
|
||||
|
@ -382,6 +411,18 @@ impl<O: ForestObligation> ObligationForest<O> {
|
|||
.insert(node.obligation.as_predicate().clone());
|
||||
}
|
||||
|
||||
fn not_waiting() -> WaitingState {
|
||||
WaitingState(0)
|
||||
}
|
||||
|
||||
fn still_waiting(&self) -> WaitingState {
|
||||
WaitingState(self.gen)
|
||||
}
|
||||
|
||||
fn is_still_waiting(&self, waiting: WaitingState) -> bool {
|
||||
waiting.0 == self.gen
|
||||
}
|
||||
|
||||
/// Performs a pass through the obligation list. This must
|
||||
/// be called in a loop until `outcome.stalled` is false.
|
||||
///
|
||||
|
@ -392,6 +433,8 @@ impl<O: ForestObligation> ObligationForest<O> {
|
|||
{
|
||||
debug!("process_obligations(len={})", self.nodes.len());
|
||||
|
||||
self.gen += 1;
|
||||
|
||||
let mut errors = vec![];
|
||||
let mut stalled = true;
|
||||
|
||||
|
@ -429,7 +472,7 @@ impl<O: ForestObligation> ObligationForest<O> {
|
|||
ProcessResult::Changed(children) => {
|
||||
// We are not (yet) stalled.
|
||||
stalled = false;
|
||||
node.state.set(NodeState::Success);
|
||||
node.state.set(NodeState::Success(Self::not_waiting()));
|
||||
|
||||
for child in children {
|
||||
let st = self.register_obligation_at(
|
||||
|
@ -464,7 +507,7 @@ impl<O: ForestObligation> ObligationForest<O> {
|
|||
};
|
||||
}
|
||||
|
||||
self.mark_as_waiting();
|
||||
self.mark_still_waiting_nodes();
|
||||
self.process_cycles(processor);
|
||||
let completed = self.compress(do_completed);
|
||||
|
||||
|
@ -477,10 +520,8 @@ impl<O: ForestObligation> ObligationForest<O> {
|
|||
}
|
||||
}
|
||||
|
||||
/// Mark all `NodeState::Success` nodes as `NodeState::Done` and
|
||||
/// report all cycles between them. This should be called
|
||||
/// after `mark_as_waiting` marks all nodes with pending
|
||||
/// subobligations as NodeState::Waiting.
|
||||
/// Report cycles between all `Success` nodes that aren't still waiting.
|
||||
/// This must be called after `mark_still_waiting_nodes`.
|
||||
fn process_cycles<P>(&self, processor: &mut P)
|
||||
where P: ObligationProcessor<Obligation=O>
|
||||
{
|
||||
|
@ -489,13 +530,15 @@ impl<O: ForestObligation> ObligationForest<O> {
|
|||
debug!("process_cycles()");
|
||||
|
||||
for (index, node) in self.nodes.iter().enumerate() {
|
||||
// For some benchmarks this state test is extremely
|
||||
// hot. It's a win to handle the no-op cases immediately to avoid
|
||||
// the cost of the function call.
|
||||
if node.state.get() == NodeState::Success {
|
||||
// For some benchmarks this state test is extremely hot. It's a win
|
||||
// to handle the no-op cases immediately to avoid the cost of the
|
||||
// function call.
|
||||
if let NodeState::Success(waiting) = node.state.get() {
|
||||
if !self.is_still_waiting(waiting) {
|
||||
self.find_cycles_from_node(&mut stack, processor, index);
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
debug!("process_cycles: complete");
|
||||
|
||||
|
@ -506,7 +549,8 @@ impl<O: ForestObligation> ObligationForest<O> {
|
|||
where P: ObligationProcessor<Obligation=O>
|
||||
{
|
||||
let node = &self.nodes[index];
|
||||
if node.state.get() == NodeState::Success {
|
||||
if let NodeState::Success(waiting) = node.state.get() {
|
||||
if !self.is_still_waiting(waiting) {
|
||||
match stack.iter().rposition(|&n| n == index) {
|
||||
None => {
|
||||
stack.push(index);
|
||||
|
@ -514,7 +558,6 @@ impl<O: ForestObligation> ObligationForest<O> {
|
|||
self.find_cycles_from_node(stack, processor, index);
|
||||
}
|
||||
stack.pop();
|
||||
node.state.set(NodeState::Done);
|
||||
}
|
||||
Some(rpos) => {
|
||||
// Cycle detected.
|
||||
|
@ -526,6 +569,7 @@ impl<O: ForestObligation> ObligationForest<O> {
|
|||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
/// Returns a vector of obligations for `p` and all of its
|
||||
/// ancestors, putting them into the error state in the process.
|
||||
|
@ -562,19 +606,14 @@ impl<O: ForestObligation> ObligationForest<O> {
|
|||
|
||||
// This always-inlined function is for the hot call site.
|
||||
#[inline(always)]
|
||||
fn inlined_mark_neighbors_as_waiting_from(&self, node: &Node<O>) {
|
||||
fn inlined_mark_dependents_as_still_waiting(&self, node: &Node<O>) {
|
||||
for &index in node.dependents.iter() {
|
||||
let node = &self.nodes[index];
|
||||
match node.state.get() {
|
||||
NodeState::Waiting | NodeState::Error => {}
|
||||
NodeState::Success => {
|
||||
node.state.set(NodeState::Waiting);
|
||||
if let NodeState::Success(waiting) = node.state.get() {
|
||||
if !self.is_still_waiting(waiting) {
|
||||
node.state.set(NodeState::Success(self.still_waiting()));
|
||||
// This call site is cold.
|
||||
self.uninlined_mark_neighbors_as_waiting_from(node);
|
||||
}
|
||||
NodeState::Pending | NodeState::Done => {
|
||||
// This call site is cold.
|
||||
self.uninlined_mark_neighbors_as_waiting_from(node);
|
||||
self.uninlined_mark_dependents_as_still_waiting(node);
|
||||
}
|
||||
}
|
||||
}
|
||||
|
@ -582,31 +621,26 @@ impl<O: ForestObligation> ObligationForest<O> {
|
|||
|
||||
// This never-inlined function is for the cold call site.
|
||||
#[inline(never)]
|
||||
fn uninlined_mark_neighbors_as_waiting_from(&self, node: &Node<O>) {
|
||||
self.inlined_mark_neighbors_as_waiting_from(node)
|
||||
}
|
||||
|
||||
/// Marks all nodes that depend on a pending node as `NodeState::Waiting`.
|
||||
fn mark_as_waiting(&self) {
|
||||
for node in &self.nodes {
|
||||
if node.state.get() == NodeState::Waiting {
|
||||
node.state.set(NodeState::Success);
|
||||
}
|
||||
fn uninlined_mark_dependents_as_still_waiting(&self, node: &Node<O>) {
|
||||
self.inlined_mark_dependents_as_still_waiting(node)
|
||||
}
|
||||
|
||||
/// Mark all `Success` nodes that depend on a pending node as still
|
||||
/// waiting. Upon completion, any `Success` nodes that aren't still waiting
|
||||
/// can be removed by `compress`.
|
||||
fn mark_still_waiting_nodes(&self) {
|
||||
for node in &self.nodes {
|
||||
if node.state.get() == NodeState::Pending {
|
||||
// This call site is hot.
|
||||
self.inlined_mark_neighbors_as_waiting_from(node);
|
||||
self.inlined_mark_dependents_as_still_waiting(node);
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
/// Compresses the vector, removing all popped nodes. This adjusts the
|
||||
/// indices and hence invalidates any outstanding indices.
|
||||
///
|
||||
/// Beforehand, all nodes must be marked as `Done` and no cycles
|
||||
/// on these nodes may be present. This is done by e.g., `process_cycles`.
|
||||
/// indices and hence invalidates any outstanding indices. `process_cycles`
|
||||
/// must be run beforehand to remove any cycles on not-still-waiting
|
||||
/// `Success` nodes.
|
||||
#[inline(never)]
|
||||
fn compress(&mut self, do_completed: DoCompleted) -> Option<Vec<O>> {
|
||||
let orig_nodes_len = self.nodes.len();
|
||||
|
@ -614,10 +648,10 @@ impl<O: ForestObligation> ObligationForest<O> {
|
|||
debug_assert!(node_rewrites.is_empty());
|
||||
node_rewrites.extend(0..orig_nodes_len);
|
||||
let mut dead_nodes = 0;
|
||||
let mut removed_done_obligations: Vec<O> = vec![];
|
||||
let mut removed_success_obligations: Vec<O> = vec![];
|
||||
|
||||
// Now move all Done/Error nodes to the end, preserving the order of
|
||||
// the Pending/Waiting nodes.
|
||||
// Move removable nodes to the end, preserving the order of the
|
||||
// remaining nodes.
|
||||
//
|
||||
// LOOP INVARIANT:
|
||||
// self.nodes[0..index - dead_nodes] are the first remaining nodes
|
||||
|
@ -626,13 +660,19 @@ impl<O: ForestObligation> ObligationForest<O> {
|
|||
for index in 0..orig_nodes_len {
|
||||
let node = &self.nodes[index];
|
||||
match node.state.get() {
|
||||
NodeState::Pending | NodeState::Waiting => {
|
||||
NodeState::Pending => {
|
||||
if dead_nodes > 0 {
|
||||
self.nodes.swap(index, index - dead_nodes);
|
||||
node_rewrites[index] -= dead_nodes;
|
||||
}
|
||||
}
|
||||
NodeState::Done => {
|
||||
NodeState::Success(waiting) if self.is_still_waiting(waiting) => {
|
||||
if dead_nodes > 0 {
|
||||
self.nodes.swap(index, index - dead_nodes);
|
||||
node_rewrites[index] -= dead_nodes;
|
||||
}
|
||||
}
|
||||
NodeState::Success(_) => {
|
||||
// This lookup can fail because the contents of
|
||||
// `self.active_cache` are not guaranteed to match those of
|
||||
// `self.nodes`. See the comment in `process_obligation`
|
||||
|
@ -646,7 +686,7 @@ impl<O: ForestObligation> ObligationForest<O> {
|
|||
}
|
||||
if do_completed == DoCompleted::Yes {
|
||||
// Extract the success stories.
|
||||
removed_done_obligations.push(node.obligation.clone());
|
||||
removed_success_obligations.push(node.obligation.clone());
|
||||
}
|
||||
node_rewrites[index] = orig_nodes_len;
|
||||
dead_nodes += 1;
|
||||
|
@ -660,7 +700,6 @@ impl<O: ForestObligation> ObligationForest<O> {
|
|||
node_rewrites[index] = orig_nodes_len;
|
||||
dead_nodes += 1;
|
||||
}
|
||||
NodeState::Success => unreachable!()
|
||||
}
|
||||
}
|
||||
|
||||
|
@ -674,7 +713,7 @@ impl<O: ForestObligation> ObligationForest<O> {
|
|||
self.node_rewrites.replace(node_rewrites);
|
||||
|
||||
if do_completed == DoCompleted::Yes {
|
||||
Some(removed_done_obligations)
|
||||
Some(removed_success_obligations)
|
||||
} else {
|
||||
None
|
||||
}
|
||||
|
|
Loading…
Reference in New Issue