Make the ControlFlowGraph reusable.

Move the flow graph computation into a compute method which can be
called with multiple functions.

This allows us to reuse the ControlFlowGraph memory and keep an instance
in the Context.

lib/cretonne/src/cfg.rs

@@ -50,31 +50,44 @@ pub struct ControlFlowGraph {
 }
 
 impl ControlFlowGraph {
-    /// During initialization mappings will be generated for any existing
-    /// blocks within the CFG's associated function.
-    pub fn new(func: &Function) -> ControlFlowGraph {
+    /// Allocate a new blank control flow graph.
+    pub fn new() -> ControlFlowGraph {
+        ControlFlowGraph {
+            entry_block: None,
+            data: EntityMap::new(),
+        }
+    }
 
-        let mut cfg = ControlFlowGraph {
-            data: EntityMap::with_capacity(func.dfg.num_ebbs()),
-            entry_block: func.layout.entry_block(),
-        };
+    /// Allocate and compute the control flow graph for `func`.
+    pub fn with_function(func: &Function) -> ControlFlowGraph {
+        let mut cfg = ControlFlowGraph::new();
+        cfg.compute(func);
+        cfg
+    }
+
+    /// Compute the control flow graph of `func`.
+    ///
+    /// This will clear and overwrite any information already stored in this data structure.
+    pub fn compute(&mut self, func: &Function) {
+        self.entry_block = func.layout.entry_block();
+        self.data.clear();
+        self.data.resize(func.dfg.num_ebbs());
 
         for ebb in &func.layout {
             for inst in func.layout.ebb_insts(ebb) {
                 match func.dfg[inst].analyze_branch() {
                     BranchInfo::SingleDest(dest, _) => {
-                        cfg.add_edge((ebb, inst), dest);
+                        self.add_edge((ebb, inst), dest);
                     }
                     BranchInfo::Table(jt) => {
                         for (_, dest) in func.jump_tables[jt].entries() {
-                            cfg.add_edge((ebb, inst), dest);
+                            self.add_edge((ebb, inst), dest);
                         }
                     }
                     BranchInfo::NotABranch => {}
                 }
             }
         }
-        cfg
     }
 
     fn add_edge(&mut self, from: BasicBlock, to: Ebb) {
@@ -140,7 +153,7 @@ mod tests {
     #[test]
     fn empty() {
         let func = Function::new();
-        let cfg = ControlFlowGraph::new(&func);
+        let cfg = ControlFlowGraph::with_function(&func);
         assert_eq!(None, cfg.ebbs().next());
     }
 
@@ -154,7 +167,7 @@ mod tests {
         func.layout.append_ebb(ebb1);
         func.layout.append_ebb(ebb2);
 
-        let cfg = ControlFlowGraph::new(&func);
+        let cfg = ControlFlowGraph::with_function(&func);
         let nodes = cfg.ebbs().collect::<Vec<_>>();
         assert_eq!(nodes.len(), 3);
 
@@ -194,7 +207,7 @@ mod tests {
             cur.insert_ebb(ebb2);
         }
 
-        let cfg = ControlFlowGraph::new(&func);
+        let cfg = ControlFlowGraph::with_function(&func);
 
         let ebb0_predecessors = cfg.get_predecessors(ebb0);
         let ebb1_predecessors = cfg.get_predecessors(ebb1);

lib/cretonne/src/context.rs

@@ -4,12 +4,16 @@
 //! deallocating the data structures needed for compilation. The `Context` struct is used to hold
 //! on to memory allocations between function compilations.
 
+use cfg::ControlFlowGraph;
 use ir::Function;
 
 /// Persistent data structures and compilation pipeline.
 pub struct Context {
     /// The function we're compiling.
     pub func: Function,
+
+    /// The control flow graph of `func`.
+    pub cfg: ControlFlowGraph,
 }
 
 impl Context {
@@ -18,6 +22,9 @@ impl Context {
     /// The returned instance should be reused for compiling multiple functions in order to avoid
     /// needless allocator thrashing.
     pub fn new() -> Context {
-        Context { func: Function::new() }
+        Context {
+            func: Function::new(),
+            cfg: ControlFlowGraph::new(),
+        }
     }
 }

lib/cretonne/src/dominator_tree.rs

@@ -203,7 +203,7 @@ mod test {
     #[test]
     fn empty() {
         let func = Function::new();
-        let cfg = ControlFlowGraph::new(&func);
+        let cfg = ControlFlowGraph::with_function(&func);
         let dtree = DominatorTree::new(&func, &cfg);
         assert_eq!(0, dtree.nodes.keys().count());
     }
@@ -238,7 +238,7 @@ mod test {
             cur.insert_ebb(ebb0);
         }
 
-        let cfg = ControlFlowGraph::new(&func);
+        let cfg = ControlFlowGraph::with_function(&func);
         let dt = DominatorTree::new(&func, &cfg);
 
         assert_eq!(func.layout.entry_block().unwrap(), ebb3);

src/filetest/domtree.rs

@@ -40,7 +40,7 @@ impl SubTest for TestDomtree {
     // Extract our own dominator tree from
     fn run(&self, func: Cow<Function>, context: &Context) -> Result<()> {
         let func = func.borrow();
-        let cfg = ControlFlowGraph::new(func);
+        let cfg = ControlFlowGraph::with_function(func);
         let domtree = DominatorTree::new(func, &cfg);
 
         // Build an expected domtree from the source annotations.

src/print_cfg.rs

@@ -33,7 +33,7 @@ impl<'a> CFGPrinter<'a> {
     pub fn new(func: &'a Function) -> CFGPrinter<'a> {
         CFGPrinter {
             func: func,
-            cfg: ControlFlowGraph::new(func),
+            cfg: ControlFlowGraph::with_function(func),
         }
     }
 

tests/cfg_traversal.rs

@@ -8,7 +8,7 @@ use self::cretonne::entity_map::EntityMap;
 
 fn test_reverse_postorder_traversal(function_source: &str, ebb_order: Vec<u32>) {
     let func = &parse_functions(function_source).unwrap()[0];
-    let cfg = ControlFlowGraph::new(&func);
+    let cfg = ControlFlowGraph::with_function(&func);
     let ebbs = ebb_order.iter()
         .map(|n| Ebb::with_number(*n).unwrap())
         .collect::<Vec<Ebb>>();