Remove the cfg::predecessors_iter() method and iterator.

This iterator enumerates all EBB references whether they are in the layout or
not. That is usually not what is needed when working with the CFG.

It is better to iterate over EBB referrences in layout order, or in reverse
post-order and then call the get_predecessors() method for each Ebb reference.

See the new implementation of print_cfg::cfg_connections().

cranelift/src/libcretonne/cfg.rs

@@ -142,34 +142,6 @@ impl ControlFlowGraph {
     pub fn len(&self) -> usize {
         self.data.len()
     }
-
-    pub fn predecessors_iter(&self) -> CFGPredecessorsIter {
-        CFGPredecessorsIter {
-            cur: 0,
-            cfg: &self,
-        }
-    }
-}
-
-/// Iterate through every mapping of ebb to predecessors in the CFG
-pub struct CFGPredecessorsIter<'a> {
-    cfg: &'a ControlFlowGraph,
-    cur: usize,
-}
-
-impl<'a> Iterator for CFGPredecessorsIter<'a> {
-    type Item = (Ebb, &'a Vec<BasicBlock>);
-
-    fn next(&mut self) -> Option<Self::Item> {
-        if self.cur < self.cfg.len() {
-            let ebb = Ebb::with_number(self.cur as u32).unwrap();
-            let bbs = self.cfg.get_predecessors(ebb);
-            self.cur += 1;
-            Some((ebb, bbs))
-        } else {
-            None
-        }
-    }
 }
 
 #[cfg(test)]
@@ -183,7 +155,7 @@ mod tests {
     fn empty() {
         let func = Function::new();
         let cfg = ControlFlowGraph::new(&func);
-        assert_eq!(None, cfg.predecessors_iter().next());
+        assert_eq!(cfg.reverse_postorder_ebbs().keys().count(), 0);
     }
 
     #[test]
@@ -197,7 +169,8 @@ mod tests {
         func.layout.append_ebb(ebb2);
 
         let cfg = ControlFlowGraph::new(&func);
-        let nodes = cfg.predecessors_iter().collect::<Vec<_>>();
+        let nodes =
+            [ebb0, ebb1, ebb2].iter().map(|&e| (e, cfg.get_predecessors(e))).collect::<Vec<_>>();
         assert_eq!(nodes.len(), 3);
 
         let mut fun_ebbs = func.layout.ebbs();