diff --git a/src/librustc_data_structures/indexed_vec.rs b/src/librustc_data_structures/indexed_vec.rs index 6f40d059be27f..6e80b48a68560 100644 --- a/src/librustc_data_structures/indexed_vec.rs +++ b/src/librustc_data_structures/indexed_vec.rs @@ -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. diff --git a/src/librustc_data_structures/obligation_forest/graphviz.rs b/src/librustc_data_structures/obligation_forest/graphviz.rs index a0363e165e049..b2120b182fa7b 100644 --- a/src/librustc_data_structures/obligation_forest/graphviz.rs +++ b/src/librustc_data_structures/obligation_forest/graphviz.rs @@ -74,9 +74,9 @@ impl<'a, O: ForestObligation + 'a> dot::GraphWalk<'a> for &'a ObligationForest 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 { /// 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>`. But that is + /// slower, because this vector is accessed so often that the + /// `u32`-to-`usize` conversions required for accesses are significant. nodes: Vec>, /// A cache of predicates that have been successfully completed. done_cache: FxHashSet, - /// 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, - scratch: Option>, + /// A scratch vector reused in various operations, to avoid allocating new + /// vectors. + scratch: RefCell>, obligation_tree_id_generator: ObligationTreeIdGenerator, @@ -178,19 +177,41 @@ struct Node { obligation: O, state: Cell, - /// 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, - /// 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, /// Identifier of the obligation tree to which this node belongs. obligation_tree_id: ObligationTreeId, } +impl Node { + fn new( + parent: Option, + obligation: O, + obligation_tree_id: ObligationTreeId + ) -> Node { + 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 ObligationForest { 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 ObligationForest { } /// 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) -> Result<(), ()> { @@ -294,15 +313,16 @@ impl ObligationForest { 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 ObligationForest { 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 ObligationForest { } /// Converts all remaining obligations to the given error. - /// - /// This cannot be done during a snapshot. pub fn to_errors(&mut self, error: E) -> Vec> { 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 ObligationForest { 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 ObligationForest { 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 ObligationForest { 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 ObligationForest { 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 ObligationForest { /// 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

(&mut self, processor: &mut P) + fn process_cycles

(&self, processor: &mut P) where P: ObligationProcessor { - 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

(&self, stack: &mut Vec, - processor: &mut P, index: usize) + fn find_cycles_from_node

(&self, stack: &mut Vec, processor: &mut P, i: usize) where P: ObligationProcessor { - 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 { - let mut error_stack = self.scratch.take().unwrap(); + fn error_at(&self, mut i: usize) -> Vec { + 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 ObligationForest { #[inline(always)] fn inlined_mark_neighbors_as_waiting_from(&self, node: &Node) { 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 ObligationForest { #[inline(never)] fn compress(&mut self, do_completed: DoCompleted) -> Option> { 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 ObligationForest { // 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 ObligationForest { } } 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 ObligationForest { // 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 ObligationForest { // 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 ObligationForest { 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 ObligationForest { 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 Node { - fn new( - parent: Option, - obligation: O, - obligation_tree_id: ObligationTreeId - ) -> Node { - 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]); diff --git a/src/librustc_data_structures/obligation_forest/node_index.rs b/src/librustc_data_structures/obligation_forest/node_index.rs deleted file mode 100644 index 69ea473e05461..0000000000000 --- a/src/librustc_data_structures/obligation_forest/node_index.rs +++ /dev/null @@ -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 - } -}