Extract the topological ordering into a module.

Multiple passes will need to iterate over EBBs in a
dominator-topological order. Move that functionality into a separate
module.

lib/cretonne/src/lib.rs

@@ -35,4 +35,5 @@ mod packed_option;
 mod partition_slice;
 mod predicates;
 mod ref_slice;
+mod topo_order;
 mod write;

lib/cretonne/src/regalloc/coloring.rs

@@ -43,19 +43,13 @@ use regalloc::affinity::Affinity;
 use regalloc::allocatable_set::AllocatableSet;
 use regalloc::live_value_tracker::{LiveValue, LiveValueTracker};
 use regalloc::liveness::Liveness;
-use sparse_map::SparseSet;
+use topo_order::TopoOrder;
 
 
 /// Data structures for the coloring pass.
 ///
 /// These are scratch space data structures that can be reused between invocations.
-pub struct Coloring {
-    /// Set of visited EBBs.
-    visited: SparseSet<Ebb>,
-
-    /// Stack of EBBs to be visited next.
-    stack: Vec<Ebb>,
-}
+pub struct Coloring {}
 
 /// Bundle of references that the coloring algorithm needs.
 ///
@@ -83,10 +77,7 @@ struct Context<'a> {
 impl Coloring {
     /// Allocate scratch space data structures for the coloring pass.
     pub fn new() -> Coloring {
-        Coloring {
-            visited: SparseSet::new(),
-            stack: Vec::new(),
-        }
+        Coloring {}
     }
 
     /// Run the coloring algorithm over `func`.
@@ -95,6 +86,7 @@ impl Coloring {
                func: &mut Function,
                domtree: &DominatorTree,
                liveness: &mut Liveness,
+               topo: &mut TopoOrder,
                tracker: &mut LiveValueTracker) {
         let mut ctx = Context {
             reginfo: isa.register_info(),
@@ -103,45 +95,17 @@ impl Coloring {
             liveness,
             usable_regs: isa.allocatable_registers(func),
         };
-        ctx.run(self, func, tracker)
+        ctx.run(func, topo, tracker)
     }
 }
 
 impl<'a> Context<'a> {
     /// Run the coloring algorithm.
-    fn run(&mut self, data: &mut Coloring, func: &mut Function, tracker: &mut LiveValueTracker) {
-        // Just visit blocks in layout order, letting `process_ebb` enforce a topological ordering.
+    fn run(&mut self, func: &mut Function, topo: &mut TopoOrder, tracker: &mut LiveValueTracker) {
+        // Just visit blocks in layout order, letting `topo` enforce a topological ordering.
         // TODO: Once we have a loop tree, we could visit hot blocks first.
-        let mut next = func.layout.entry_block();
-        while let Some(ebb) = next {
-            self.process_ebb(ebb, data, func, tracker);
-            next = func.layout.next_ebb(ebb);
-        }
-    }
-
-    /// Process `ebb`, but only after ensuring that the immediate dominator has been processed.
-    ///
-    /// This method can be called with the most desired order of visiting the EBBs. It will convert
-    /// that order into a valid topological order by visiting dominators first.
-    fn process_ebb(&mut self,
-                   mut ebb: Ebb,
-                   data: &mut Coloring,
-                   func: &mut Function,
-                   tracker: &mut LiveValueTracker) {
-        // The stack is just a scratch space for this algorithm. We leave it empty when returning.
-        assert!(data.stack.is_empty());
-
-        // Trace up the dominator tree until we reach a dominator that has already been visited.
-        while data.visited.insert(ebb).is_none() {
-            data.stack.push(ebb);
-            match self.domtree.idom(ebb) {
-                Some(idom) => ebb = func.layout.inst_ebb(idom).expect("idom not in layout"),
-                None => break,
-            }
-        }
-
-        // Pop off blocks in topological order.
-        while let Some(ebb) = data.stack.pop() {
+        topo.reset(func.layout.ebbs());
+        while let Some(ebb) = topo.next(&func.layout, self.domtree) {
             self.visit_ebb(ebb, func, tracker);
         }
     }

lib/cretonne/src/regalloc/context.rs

@@ -12,11 +12,13 @@ use regalloc::coloring::Coloring;
 use regalloc::live_value_tracker::LiveValueTracker;
 use regalloc::liveness::Liveness;
 use result::CtonResult;
+use topo_order::TopoOrder;
 use verifier::{verify_context, verify_liveness};
 
 /// Persistent memory allocations for register allocation.
 pub struct Context {
     liveness: Liveness,
+    topo: TopoOrder,
     tracker: LiveValueTracker,
     coloring: Coloring,
 }
@@ -29,6 +31,7 @@ impl Context {
     pub fn new() -> Context {
         Context {
             liveness: Liveness::new(),
+            topo: TopoOrder::new(),
             tracker: LiveValueTracker::new(),
             coloring: Coloring::new(),
         }
@@ -60,7 +63,12 @@ impl Context {
 
         // Third pass: Reload and coloring.
         self.coloring
-            .run(isa, func, domtree, &mut self.liveness, &mut self.tracker);
+            .run(isa,
+                 func,
+                 domtree,
+                 &mut self.liveness,
+                 &mut self.topo,
+                 &mut self.tracker);
 
         if isa.flags().enable_verifier() {
             verify_context(func, cfg, domtree, Some(isa))?;

lib/cretonne/src/topo_order.rs

@@ -0,0 +1,125 @@
+//! Topological order of EBBs, according to the dominator tree.
+
+use dominator_tree::DominatorTree;
+use ir::{Ebb, Layout};
+use sparse_map::SparseSet;
+
+/// Present EBBs in a topological order such that all dominating EBBs are guaranteed to be visited
+/// before the current EBB.
+///
+/// There are many topological orders of the EBBs in a function, so it is possible to provide a
+/// preferred order, and the `TopoOrder` will present EBBs in an order that is as close as possible
+/// to the preferred order.
+pub struct TopoOrder {
+    /// Preferred order of EBBs to visit.
+    preferred: Vec<Ebb>,
+
+    /// Next entry to get from `preferred`.
+    next: usize,
+
+    /// Set of visited EBBs.
+    visited: SparseSet<Ebb>,
+
+    /// Stack of EBBs to be visited next, already in `visited`.
+    stack: Vec<Ebb>,
+}
+
+impl TopoOrder {
+    /// Create a new empty topological order.
+    pub fn new() -> TopoOrder {
+        TopoOrder {
+            preferred: Vec::new(),
+            next: 0,
+            visited: SparseSet::new(),
+            stack: Vec::new(),
+        }
+    }
+
+    /// Reset and initialize with a preferred sequence of EBBs. The resulting topological order is
+    /// guaranteed to contain all of the EBBs in `preferred` as well as any dominators.
+    pub fn reset<Ebbs>(&mut self, preferred: Ebbs)
+        where Ebbs: IntoIterator<Item = Ebb>
+    {
+        self.preferred.clear();
+        self.preferred.extend(preferred);
+        self.next = 0;
+        self.visited.clear();
+        self.stack.clear();
+    }
+
+    /// Get the next EBB in the topological order.
+    ///
+    /// Two things are guaranteed about the EBBs returned by this function:
+    ///
+    /// - All EBBs in the `preferred` iterator given to `reset` will be returned.
+    /// - All dominators are visited before the EBB returned.
+    pub fn next(&mut self, layout: &Layout, domtree: &DominatorTree) -> Option<Ebb> {
+        // Any entries in `stack` should be returned immediately. They have already been added to
+        // `visited`.
+        while self.stack.is_empty() {
+            match self.preferred.get(self.next).cloned() {
+                None => return None,
+                Some(mut ebb) => {
+                    // We have the next EBB in the preferred order.
+                    self.next += 1;
+                    // Push it along with any non-visited dominators.
+                    while self.visited.insert(ebb).is_none() {
+                        self.stack.push(ebb);
+                        match domtree.idom(ebb) {
+                            Some(idom) => ebb = layout.inst_ebb(idom).expect("idom not in layout"),
+                            None => break,
+                        }
+                    }
+                }
+            }
+        }
+        return self.stack.pop();
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use flowgraph::ControlFlowGraph;
+    use dominator_tree::DominatorTree;
+    use ir::{Function, InstBuilder, Cursor};
+    use std::iter;
+    use super::*;
+
+    #[test]
+    fn empty() {
+        let func = Function::new();
+        let cfg = ControlFlowGraph::with_function(&func);
+        let domtree = DominatorTree::with_function(&func, &cfg);
+        let mut topo = TopoOrder::new();
+
+        assert_eq!(topo.next(&func.layout, &domtree), None);
+        topo.reset(func.layout.ebbs());
+        assert_eq!(topo.next(&func.layout, &domtree), None);
+    }
+
+    #[test]
+    fn simple() {
+        let mut func = Function::new();
+        let ebb0 = func.dfg.make_ebb();
+        let ebb1 = func.dfg.make_ebb();
+
+        {
+            let dfg = &mut func.dfg;
+            let cur = &mut Cursor::new(&mut func.layout);
+
+            cur.insert_ebb(ebb0);
+            dfg.ins(cur).jump(ebb1, &[]);
+            cur.insert_ebb(ebb1);
+            dfg.ins(cur).jump(ebb1, &[]);
+        }
+
+        let cfg = ControlFlowGraph::with_function(&func);
+        let domtree = DominatorTree::with_function(&func, &cfg);
+        let mut topo = TopoOrder::new();
+
+        topo.reset(iter::once(ebb1));
+        assert_eq!(topo.next(&func.layout, &domtree), Some(ebb0));
+        assert_eq!(topo.next(&func.layout, &domtree), Some(ebb1));
+        assert_eq!(topo.next(&func.layout, &domtree), None);
+    }
+}