Auto merge of #51987 - nikomatsakis:nll-region-infer-scc, r=pnkfelix

nll experiment: compute SCCs instead of iterative region solving

This is an attempt to speed up region solving by replacing the current iterative dataflow with a SCC computation. The idea is to detect cycles (SCCs) amongst region constraints and then compute just one value per cycle. The graph with all cycles removed is of course a DAG, so we can then solve constraints "bottom up" once the liveness values are known.

I kinda ran out of time this morning so the last commit is a bit sloppy but I wanted to get this posted, let travis run on it, and maybe do a perf run, before I clean it up.

Author: bors

src/librustc/cfg/construct.rs

@@ -8,11 +8,11 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use rustc_data_structures::graph;
 use cfg::*;
 use middle::region;
-use ty::{self, TyCtxt};
+use rustc_data_structures::graph::implementation as graph;
 use syntax::ptr::P;
+use ty::{self, TyCtxt};
 
 use hir::{self, PatKind};
 use hir::def_id::DefId;

src/librustc/cfg/mod.rs

@@ -11,7 +11,7 @@
 //! Module that constructs a control-flow graph representing an item.
 //! Uses `Graph` as the underlying representation.
 
-use rustc_data_structures::graph;
+use rustc_data_structures::graph::implementation as graph;
 use ty::TyCtxt;
 use hir;
 use hir::def_id::DefId;

src/librustc/dep_graph/query.rs

@@ -9,7 +9,9 @@
 // except according to those terms.
 
 use rustc_data_structures::fx::FxHashMap;
-use rustc_data_structures::graph::{Direction, INCOMING, Graph, NodeIndex, OUTGOING};
+use rustc_data_structures::graph::implementation::{
+    Direction, INCOMING, Graph, NodeIndex, OUTGOING
+};
 
 use super::DepNode;
 

src/librustc/infer/lexical_region_resolve/mod.rs

@@ -20,7 +20,7 @@ use infer::region_constraints::VerifyBound;
 use middle::free_region::RegionRelations;
 use rustc_data_structures::indexed_vec::{Idx, IndexVec};
 use rustc_data_structures::fx::FxHashSet;
-use rustc_data_structures::graph::{self, Direction, NodeIndex, OUTGOING};
+use rustc_data_structures::graph::implementation::{Graph, Direction, NodeIndex, INCOMING, OUTGOING};
 use std::fmt;
 use std::u32;
 use ty::{self, TyCtxt};
@@ -99,7 +99,7 @@ struct RegionAndOrigin<'tcx> {
     origin: SubregionOrigin<'tcx>,
 }
 
-type RegionGraph<'tcx> = graph::Graph<(), Constraint<'tcx>>;
+type RegionGraph<'tcx> = Graph<(), Constraint<'tcx>>;
 
 struct LexicalResolver<'cx, 'gcx: 'tcx, 'tcx: 'cx> {
     region_rels: &'cx RegionRelations<'cx, 'gcx, 'tcx>,
@@ -501,7 +501,7 @@ impl<'cx, 'gcx, 'tcx> LexicalResolver<'cx, 'gcx, 'tcx> {
     fn construct_graph(&self) -> RegionGraph<'tcx> {
         let num_vars = self.num_vars();
 
-        let mut graph = graph::Graph::new();
+        let mut graph = Graph::new();
 
         for _ in 0..num_vars {
             graph.add_node(());
@@ -550,9 +550,9 @@ impl<'cx, 'gcx, 'tcx> LexicalResolver<'cx, 'gcx, 'tcx> {
         // Errors in expanding nodes result from a lower-bound that is
         // not contained by an upper-bound.
         let (mut lower_bounds, lower_dup) =
-            self.collect_concrete_regions(graph, node_idx, graph::INCOMING, dup_vec);
+            self.collect_concrete_regions(graph, node_idx, INCOMING, dup_vec);
         let (mut upper_bounds, upper_dup) =
-            self.collect_concrete_regions(graph, node_idx, graph::OUTGOING, dup_vec);
+            self.collect_concrete_regions(graph, node_idx, OUTGOING, dup_vec);
 
         if lower_dup || upper_dup {
             return;

src/librustc/middle/dataflow.rs

@@ -22,7 +22,7 @@ use std::mem;
 use std::usize;
 use syntax::print::pprust::PrintState;
 
-use rustc_data_structures::graph::OUTGOING;
+use rustc_data_structures::graph::implementation::OUTGOING;
 
 use util::nodemap::FxHashMap;
 use hir;

src/librustc/mir/mod.rs

@@ -21,9 +21,8 @@ use mir::interpret::{EvalErrorKind, Scalar, Value};
 use mir::visit::MirVisitable;
 use rustc_apfloat::ieee::{Double, Single};
 use rustc_apfloat::Float;
-use rustc_data_structures::control_flow_graph::dominators::{dominators, Dominators};
-use rustc_data_structures::control_flow_graph::ControlFlowGraph;
-use rustc_data_structures::control_flow_graph::{GraphPredecessors, GraphSuccessors};
+use rustc_data_structures::graph::dominators::{dominators, Dominators};
+use rustc_data_structures::graph::{self, GraphPredecessors, GraphSuccessors};
 use rustc_data_structures::indexed_vec::{Idx, IndexVec};
 use rustc_data_structures::small_vec::SmallVec;
 use rustc_data_structures::sync::Lrc;
@@ -2289,23 +2288,32 @@ fn item_path_str(def_id: DefId) -> String {
     ty::tls::with(|tcx| tcx.item_path_str(def_id))
 }
 
-impl<'tcx> ControlFlowGraph for Mir<'tcx> {
+impl<'tcx> graph::DirectedGraph for Mir<'tcx> {
     type Node = BasicBlock;
+}
 
+impl<'tcx> graph::WithNumNodes for Mir<'tcx> {
     fn num_nodes(&self) -> usize {
         self.basic_blocks.len()
     }
+}
 
+impl<'tcx> graph::WithStartNode for Mir<'tcx> {
     fn start_node(&self) -> Self::Node {
         START_BLOCK
     }
+}
 
+impl<'tcx> graph::WithPredecessors for Mir<'tcx> {
     fn predecessors<'graph>(
         &'graph self,
         node: Self::Node,
     ) -> <Self as GraphPredecessors<'graph>>::Iter {
         self.predecessors_for(node).clone().into_iter()
     }
+}
+
+impl<'tcx> graph::WithSuccessors for Mir<'tcx> {
     fn successors<'graph>(
         &'graph self,
         node: Self::Node,
@@ -2314,12 +2322,12 @@ impl<'tcx> ControlFlowGraph for Mir<'tcx> {
     }
 }
 
-impl<'a, 'b> GraphPredecessors<'b> for Mir<'a> {
+impl<'a, 'b> graph::GraphPredecessors<'b> for Mir<'a> {
     type Item = BasicBlock;
     type Iter = IntoIter<BasicBlock>;
 }
 
-impl<'a, 'b> GraphSuccessors<'b> for Mir<'a> {
+impl<'a, 'b> graph::GraphSuccessors<'b> for Mir<'a> {
     type Item = BasicBlock;
     type Iter = iter::Cloned<Successors<'b>>;
 }

src/librustc_codegen_llvm/mir/analyze.rs

@@ -12,7 +12,7 @@
 //! which do not.
 
 use rustc_data_structures::bitvec::BitVector;
-use rustc_data_structures::control_flow_graph::dominators::Dominators;
+use rustc_data_structures::graph::dominators::Dominators;
 use rustc_data_structures::indexed_vec::{Idx, IndexVec};
 use rustc::mir::{self, Location, TerminatorKind};
 use rustc::mir::visit::{Visitor, PlaceContext};

src/librustc_data_structures/control_flow_graph/mod.rs

@@ -14,9 +14,9 @@
 //! Rice Computer Science TS-06-33870
 //! <https://www.cs.rice.edu/~keith/EMBED/dom.pdf>
 
-use super::ControlFlowGraph;
+use super::super::indexed_vec::{Idx, IndexVec};
 use super::iterate::reverse_post_order;
-use super::super::indexed_vec::{IndexVec, Idx};
+use super::ControlFlowGraph;
 
 use std::fmt;
 
@@ -29,15 +29,16 @@ pub fn dominators<G: ControlFlowGraph>(graph: &G) -> Dominators<G::Node> {
     dominators_given_rpo(graph, &rpo)
 }
 
-pub fn dominators_given_rpo<G: ControlFlowGraph>(graph: &G,
-                                                 rpo: &[G::Node])
-                                                 -> Dominators<G::Node> {
+pub fn dominators_given_rpo<G: ControlFlowGraph>(
+    graph: &G,
+    rpo: &[G::Node],
+) -> Dominators<G::Node> {
     let start_node = graph.start_node();
     assert_eq!(rpo[0], start_node);
 
     // compute the post order index (rank) for each node
-    let mut post_order_rank: IndexVec<G::Node, usize> = IndexVec::from_elem_n(usize::default(),
-                                                                              graph.num_nodes());
+    let mut post_order_rank: IndexVec<G::Node, usize> =
+        IndexVec::from_elem_n(usize::default(), graph.num_nodes());
     for (index, node) in rpo.iter().rev().cloned().enumerate() {
         post_order_rank[node] = index;
     }
@@ -56,10 +57,12 @@ pub fn dominators_given_rpo<G: ControlFlowGraph>(graph: &G,
                 if immediate_dominators[pred].is_some() {
                     // (*)
                     // (*) dominators for `pred` have been calculated
-                    new_idom = intersect_opt(&post_order_rank,
-                                             &immediate_dominators,
-                                             new_idom,
-                                             Some(pred));
+                    new_idom = intersect_opt(
+                        &post_order_rank,
+                        &immediate_dominators,
+                        new_idom,
+                        Some(pred),
+                    );
                 }
             }
 
@@ -76,23 +79,25 @@ pub fn dominators_given_rpo<G: ControlFlowGraph>(graph: &G,
     }
 }
 
-fn intersect_opt<Node: Idx>(post_order_rank: &IndexVec<Node, usize>,
-                            immediate_dominators: &IndexVec<Node, Option<Node>>,
-                            node1: Option<Node>,
-                            node2: Option<Node>)
-                            -> Option<Node> {
+fn intersect_opt<Node: Idx>(
+    post_order_rank: &IndexVec<Node, usize>,
+    immediate_dominators: &IndexVec<Node, Option<Node>>,
+    node1: Option<Node>,
+    node2: Option<Node>,
+) -> Option<Node> {
     match (node1, node2) {
         (None, None) => None,
         (Some(n), None) | (None, Some(n)) => Some(n),
         (Some(n1), Some(n2)) => Some(intersect(post_order_rank, immediate_dominators, n1, n2)),
     }
 }
 
-fn intersect<Node: Idx>(post_order_rank: &IndexVec<Node, usize>,
-                        immediate_dominators: &IndexVec<Node, Option<Node>>,
-                        mut node1: Node,
-                        mut node2: Node)
-                        -> Node {
+fn intersect<Node: Idx>(
+    post_order_rank: &IndexVec<Node, usize>,
+    immediate_dominators: &IndexVec<Node, Option<Node>>,
+    mut node1: Node,
+    mut node2: Node,
+) -> Node {
     while node1 != node2 {
         while post_order_rank[node1] < post_order_rank[node2] {
             node1 = immediate_dominators[node1].unwrap();
@@ -176,11 +181,13 @@ impl<Node: Idx> DominatorTree<Node> {
 
 impl<Node: Idx> fmt::Debug for DominatorTree<Node> {
     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
-        fmt::Debug::fmt(&DominatorTreeNode {
-                            tree: self,
-                            node: self.root,
-                        },
-                        fmt)
+        fmt::Debug::fmt(
+            &DominatorTreeNode {
+                tree: self,
+                node: self.root,
+            },
+            fmt,
+        )
     }
 }
 
@@ -194,11 +201,9 @@ impl<'tree, Node: Idx> fmt::Debug for DominatorTreeNode<'tree, Node> {
         let subtrees: Vec<_> = self.tree
             .children(self.node)
             .iter()
-            .map(|&child| {
-                DominatorTreeNode {
-                    tree: self.tree,
-                    node: child,
-                }
+            .map(|&child| DominatorTreeNode {
+                tree: self.tree,
+                node: child,
             })
             .collect();
         fmt.debug_tuple("")