auto merge of #7688 : nikomatsakis/rust/issue-6298-dataflow-graph, r=graydon

This patch is a step towards #6298. It extracts the graph abstraction from region inference into a library, and then ports the region inference to use it. It also adds a control-flow graph abstraction that will eventually be used by dataflow. The CFG code is not yet used, but I figured better to add it so as to make later rebasing etc easier.

Author: bors

src/librustc/middle/cfg/construct.rs

@@ -0,0 +1,61 @@
+// Copyright 2012 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.
+
+/*!
+
+Module that constructs a control-flow graph representing an item.
+Uses `Graph` as the underlying representation.
+
+*/
+
+use middle::graph;
+use middle::ty;
+use middle::typeck;
+use std::hashmap::HashMap;
+use syntax::ast;
+use syntax::opt_vec::OptVec;
+
+mod construct;
+
+pub struct CFG {
+    exit_map: HashMap<ast::node_id, CFGIndex>,
+    graph: CFGGraph,
+    entry: CFGIndex,
+    exit: CFGIndex,
+}
+
+pub struct CFGNodeData {
+    id: ast::node_id
+}
+
+pub struct CFGEdgeData {
+    exiting_scopes: OptVec<ast::node_id>
+}
+
+pub type CFGIndex = graph::NodeIndex;
+
+pub type CFGGraph = graph::Graph<CFGNodeData, CFGEdgeData>;
+
+pub type CFGNode = graph::Node<CFGNodeData>;
+
+pub type CFGEdge = graph::Edge<CFGEdgeData>;
+
+pub struct CFGIndices {
+    entry: CFGIndex,
+    exit: CFGIndex,
+}
+
+impl CFG {
+    pub fn new(tcx: ty::ctxt,
+               method_map: typeck::method_map,
+               blk: &ast::blk) -> CFG {
+        construct::construct(tcx, method_map, blk)
+    }
+}