Rollup merge of rust-lang#24209 - nikomatsakis:refactor-unification, r=nrc

 I'm on a quest to slowly refactor a lot of the inference code. A first step for that is moving the \"pure data structures\" out so as to simplify what's left. This PR moves `snapshot_vec`, `graph`, and `unify` into their own crate (`librustc_data_structures`). They can then be unit-tested, benchmarked, etc more easily. As a benefit, I improved the performance of unification slightly on the benchmark I added vs the original code.

r? @nrc

Author: Manishearth

mk/crates.mk

@@ -54,7 +54,8 @@ TARGET_CRATES := libc std flate arena term \
                  log graphviz core rbml alloc \
                  unicode rustc_bitflags
 RUSTC_CRATES := rustc rustc_typeck rustc_borrowck rustc_resolve rustc_driver \
-                rustc_trans rustc_back rustc_llvm rustc_privacy rustc_lint
+                rustc_trans rustc_back rustc_llvm rustc_privacy rustc_lint \
+                rustc_data_structures
 HOST_CRATES := syntax $(RUSTC_CRATES) rustdoc fmt_macros
 CRATES := $(TARGET_CRATES) $(HOST_CRATES)
 TOOLS := compiletest rustdoc rustc rustbook
@@ -80,9 +81,10 @@ DEPS_rustc_resolve := rustc log syntax
 DEPS_rustc_privacy := rustc log syntax
 DEPS_rustc_lint := rustc log syntax
 DEPS_rustc := syntax flate arena serialize getopts rbml \
-              log graphviz rustc_llvm rustc_back
+              log graphviz rustc_llvm rustc_back rustc_data_structures
 DEPS_rustc_llvm := native:rustllvm libc std
 DEPS_rustc_back := std syntax rustc_llvm flate log libc
+DEPS_rustc_data_structures := std log serialize
 DEPS_rustdoc := rustc rustc_driver native:hoedown serialize getopts \
                 test rustc_lint
 DEPS_rustc_bitflags := core
@@ -141,16 +143,17 @@ DOC_CRATES := $(filter-out rustc, \
 	   $(filter-out rustc_trans, \
 	   $(filter-out rustc_typeck, \
 	   $(filter-out rustc_borrowck, \
+	   $(filter-out rustc_data_structures, \
 	   $(filter-out rustc_resolve, \
 	   $(filter-out rustc_driver, \
 	   $(filter-out rustc_privacy, \
 	   $(filter-out rustc_lint, \
 	   $(filter-out log, \
 	   $(filter-out getopts, \
-	   $(filter-out syntax, $(CRATES))))))))))))
+	   $(filter-out syntax, $(CRATES)))))))))))))
 #endif
 #endif
-COMPILER_DOC_CRATES := rustc rustc_trans rustc_borrowck rustc_resolve \
+COMPILER_DOC_CRATES := rustc rustc_trans rustc_borrowck rustc_data_structures rustc_resolve \
                        rustc_typeck rustc_driver syntax rustc_privacy \
                        rustc_lint
 

src/librustc/lib.rs

@@ -54,6 +54,7 @@ extern crate graphviz;
 extern crate libc;
 extern crate rustc_llvm;
 extern crate rustc_back;
+extern crate rustc_data_structures;
 extern crate serialize;
 extern crate rbml;
 extern crate collections;
@@ -103,7 +104,6 @@ pub mod middle {
     pub mod entry;
     pub mod expr_use_visitor;
     pub mod fast_reject;
-    pub mod graph;
     pub mod intrinsicck;
     pub mod infer;
     pub mod lang_items;
@@ -141,7 +141,6 @@ pub mod util {
     pub mod common;
     pub mod ppaux;
     pub mod nodemap;
-    pub mod snapshot_vec;
     pub mod lev_distance;
 }
 

src/librustc/middle/cfg/construct.rs

@@ -8,9 +8,9 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use rustc_data_structures::graph;
 use middle::cfg::*;
 use middle::def;
-use middle::graph;
 use middle::pat_util;
 use middle::region::CodeExtent;
 use middle::ty;

src/librustc/middle/cfg/mod.rs

@@ -11,7 +11,7 @@
 //! Module that constructs a control-flow graph representing an item.
 //! Uses `Graph` as the underlying representation.
 
-use middle::graph;
+use rustc_data_structures::graph;
 use middle::ty;
 use syntax::ast;
 
@@ -24,7 +24,7 @@ pub struct CFG {
     pub exit: CFGIndex,
 }
 
-#[derive(Copy, Clone, PartialEq)]
+#[derive(Copy, Clone, Debug, PartialEq)]
 pub enum CFGNodeData {
     AST(ast::NodeId),
     Entry,
@@ -43,6 +43,7 @@ impl CFGNodeData {
     }
 }
 
+#[derive(Debug)]
 pub struct CFGEdgeData {
     pub exiting_scopes: Vec<ast::NodeId>
 }

src/librustc/middle/dataflow.rs

@@ -530,10 +530,9 @@ impl<'a, 'b, 'tcx, O:DataFlowOperator> PropagationContext<'a, 'b, 'tcx, O> {
                                                pred_bits: &[usize],
                                                cfg: &cfg::CFG,
                                                cfgidx: CFGIndex) {
-        cfg.graph.each_outgoing_edge(cfgidx, |_e_idx, edge| {
+        for (_, edge) in cfg.graph.outgoing_edges(cfgidx) {
             self.propagate_bits_into_entry_set_for(pred_bits, edge);
-            true
-        });
+        }
     }
 
     fn propagate_bits_into_entry_set_for(&mut self,

src/librustc/middle/infer/freshen.rs

@@ -37,7 +37,7 @@ use middle::ty_fold::TypeFolder;
 use std::collections::hash_map::{self, Entry};
 
 use super::InferCtxt;
-use super::unify::ToType;
+use super::unify_key::ToType;
 
 pub struct TypeFreshener<'a, 'tcx:'a> {
     infcx: &'a InferCtxt<'a, 'tcx>,

src/librustc/middle/infer/mod.rs

@@ -29,6 +29,7 @@ use middle::ty::replace_late_bound_regions;
 use middle::ty::{self, Ty};
 use middle::ty_fold::{TypeFolder, TypeFoldable};
 use middle::ty_relate::{Relate, RelateResult, TypeRelation};
+use rustc_data_structures::unify::{self, UnificationTable};
 use std::cell::{RefCell};
 use std::fmt;
 use std::rc::Rc;
@@ -41,8 +42,8 @@ use util::ppaux::{Repr, UserString};
 
 use self::combine::CombineFields;
 use self::region_inference::{RegionVarBindings, RegionSnapshot};
-use self::unify::{ToType, UnificationTable};
 use self::error_reporting::ErrorReporting;
+use self::unify_key::ToType;
 
 pub mod bivariate;
 pub mod combine;
@@ -57,7 +58,7 @@ pub mod resolve;
 mod freshen;
 pub mod sub;
 pub mod type_variable;
-pub mod unify;
+pub mod unify_key;
 
 pub type Bound<T> = Option<T>;
 pub type UnitResult<'tcx> = RelateResult<'tcx, ()>; // "unify result"

src/librustc/middle/infer/region_inference/mod.rs

@@ -20,14 +20,13 @@ use self::Classification::*;
 
 use super::{RegionVariableOrigin, SubregionOrigin, TypeTrace, MiscVariable};
 
+use rustc_data_structures::graph::{self, Direction, NodeIndex};
 use middle::region;
 use middle::ty::{self, Ty};
 use middle::ty::{BoundRegion, FreeRegion, Region, RegionVid};
 use middle::ty::{ReEmpty, ReStatic, ReInfer, ReFree, ReEarlyBound};
 use middle::ty::{ReLateBound, ReScope, ReVar, ReSkolemized, BrFresh};
 use middle::ty_relate::RelateResult;
-use middle::graph;
-use middle::graph::{Direction, NodeIndex};
 use util::common::indenter;
 use util::nodemap::{FnvHashMap, FnvHashSet};
 use util::ppaux::{Repr, UserString};
@@ -1325,10 +1324,8 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> {
         let num_vars = self.num_vars();
 
         let constraints = self.constraints.borrow();
-        let num_edges = constraints.len();
 
-        let mut graph = graph::Graph::with_capacity(num_vars as usize + 1,
-                                                    num_edges);
+        let mut graph = graph::Graph::new();
 
         for _ in 0..num_vars {
             graph.add_node(());
@@ -1370,10 +1367,10 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> {
         // not contained by an upper-bound.
         let (mut lower_bounds, lower_dup) =
             self.collect_concrete_regions(graph, var_data, node_idx,
-                                          graph::Incoming, dup_vec);
+                                          graph::INCOMING, dup_vec);
         let (mut upper_bounds, upper_dup) =
             self.collect_concrete_regions(graph, var_data, node_idx,
-                                          graph::Outgoing, dup_vec);
+                                          graph::OUTGOING, dup_vec);
 
         if lower_dup || upper_dup {
             return;
@@ -1433,7 +1430,7 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> {
         // that have no intersection.
         let (upper_bounds, dup_found) =
             self.collect_concrete_regions(graph, var_data, node_idx,
-                                          graph::Outgoing, dup_vec);
+                                          graph::OUTGOING, dup_vec);
 
         if dup_found {
             return;
@@ -1508,8 +1505,8 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> {
             // figure out the direction from which this node takes its
             // values, and search for concrete regions etc in that direction
             let dir = match classification {
-                Expanding => graph::Incoming,
-                Contracting => graph::Outgoing,
+                Expanding => graph::INCOMING,
+                Contracting => graph::OUTGOING,
             };
 
             process_edges(self, &mut state, graph, node_idx, dir);
@@ -1519,14 +1516,14 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> {
         return (result, dup_found);
 
         fn process_edges<'a, 'tcx>(this: &RegionVarBindings<'a, 'tcx>,
-                         state: &mut WalkState<'tcx>,
-                         graph: &RegionGraph,
-                         source_vid: RegionVid,
-                         dir: Direction) {
+                                   state: &mut WalkState<'tcx>,
+                                   graph: &RegionGraph,
+                                   source_vid: RegionVid,
+                                   dir: Direction) {
             debug!("process_edges(source_vid={:?}, dir={:?})", source_vid, dir);
 
             let source_node_index = NodeIndex(source_vid.index as usize);
-            graph.each_adjacent_edge(source_node_index, dir, |_, edge| {
+            for (_, edge) in graph.adjacent_edges(source_node_index, dir) {
                 match edge.data {
                     ConstrainVarSubVar(from_vid, to_vid) => {
                         let opp_vid =
@@ -1544,8 +1541,7 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> {
                         });
                     }
                 }
-                true
-            });
+            }
         }
     }
 

src/librustc/middle/infer/type_variable.rs

@@ -17,7 +17,7 @@ use std::cmp::min;
 use std::marker::PhantomData;
 use std::mem;
 use std::u32;
-use util::snapshot_vec as sv;
+use rustc_data_structures::snapshot_vec as sv;
 
 pub struct TypeVariableTable<'tcx> {
     values: sv::SnapshotVec<Delegate<'tcx>>,
@@ -65,7 +65,7 @@ impl RelationDir {
 
 impl<'tcx> TypeVariableTable<'tcx> {
     pub fn new() -> TypeVariableTable<'tcx> {
-        TypeVariableTable { values: sv::SnapshotVec::new(Delegate(PhantomData)) }
+        TypeVariableTable { values: sv::SnapshotVec::new() }
     }
 
     fn relations<'a>(&'a mut self, a: ty::TyVid) -> &'a mut Vec<Relation> {
@@ -201,9 +201,7 @@ impl<'tcx> sv::SnapshotVecDelegate for Delegate<'tcx> {
     type Value = TypeVariableData<'tcx>;
     type Undo = UndoEntry;
 
-    fn reverse(&mut self,
-               values: &mut Vec<TypeVariableData<'tcx>>,
-               action: UndoEntry) {
+    fn reverse(values: &mut Vec<TypeVariableData<'tcx>>, action: UndoEntry) {
         match action {
             SpecifyVar(vid, relations) => {
                 values[vid.index as usize].value = Bounded(relations);

src/librustc/middle/infer/unify_key.rs

@@ -0,0 +1,48 @@
+// 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.
+
+use middle::ty::{self, IntVarValue, Ty};
+use rustc_data_structures::unify::UnifyKey;
+use syntax::ast;
+
+pub trait ToType<'tcx> {
+    fn to_type(&self, tcx: &ty::ctxt<'tcx>) -> Ty<'tcx>;
+}
+
+impl UnifyKey for ty::IntVid {
+    type Value = Option<IntVarValue>;
+    fn index(&self) -> u32 { self.index }
+    fn from_index(i: u32) -> ty::IntVid { ty::IntVid { index: i } }
+    fn tag(_: Option<ty::IntVid>) -> &'static str { "IntVid" }
+}
+
+impl<'tcx> ToType<'tcx> for IntVarValue {
+    fn to_type(&self, tcx: &ty::ctxt<'tcx>) -> Ty<'tcx> {
+        match *self {
+            ty::IntType(i) => ty::mk_mach_int(tcx, i),
+            ty::UintType(i) => ty::mk_mach_uint(tcx, i),
+        }
+    }
+}
+
+// Floating point type keys
+
+impl UnifyKey for ty::FloatVid {
+    type Value = Option<ast::FloatTy>;
+    fn index(&self) -> u32 { self.index }
+    fn from_index(i: u32) -> ty::FloatVid { ty::FloatVid { index: i } }
+    fn tag(_: Option<ty::FloatVid>) -> &'static str { "FloatVid" }
+}
+
+impl<'tcx> ToType<'tcx> for ast::FloatTy {
+    fn to_type(&self, tcx: &ty::ctxt<'tcx>) -> Ty<'tcx> {
+        ty::mk_mach_float(tcx, *self)
+    }
+}

src/librustc_data_structures/bitvec.rs

@@ -0,0 +1,42 @@
+// Copyright 2015 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.
+
+use std::iter;
+
+/// A very simple BitVector type.
+pub struct BitVector {
+    data: Vec<u64>
+}
+
+impl BitVector {
+    pub fn new(num_bits: usize) -> BitVector {
+        let num_words = (num_bits + 63) / 64;
+        BitVector { data: iter::repeat(0).take(num_words).collect() }
+    }
+
+    fn word_mask(&self, bit: usize) -> (usize, u64) {
+        let word = bit / 64;
+        let mask = 1 << (bit % 64);
+        (word, mask)
+    }
+
+    pub fn contains(&self, bit: usize) -> bool {
+        let (word, mask) = self.word_mask(bit);
+        (self.data[word] & mask) != 0
+    }
+
+    pub fn insert(&mut self, bit: usize) -> bool {
+        let (word, mask) = self.word_mask(bit);
+        let data = &mut self.data[word];
+        let value = *data;
+        *data = value | mask;
+        (value | mask) != value
+    }
+}