Initial support for polymorphic inlining.

runtime/vm/flow_graph.cc

Index: runtime/vm/flow_graph.cc
diff --git a/runtime/vm/flow_graph.cc b/runtime/vm/flow_graph.cc
index 34ca6932d6aad8b34e57e39fe44fab42b493ba5d..6157a160756049d76e732e80ba8ece9715b067ca 100644
--- a/runtime/vm/flow_graph.cc
+++ b/runtime/vm/flow_graph.cc
@@ -847,6 +847,24 @@ void FlowGraph::RemoveDeadPhis(GrowableArray<PhiInstr*>* live_phis) {
 }
 
 
+void FlowGraph::RemoveRedefinitions() {

[Florian Schneider, 2013/05/03 10:41:36]

This is very similar to what we do with ConstraintInstr after array bounds check
elimination. Could you share the code?

[Kevin Millikin (Google), 2013/05/03 11:47:38]

That one uses a maintained list of constraints, this one searches in the graph
for redefinitions.  I don't really want to maintain a list of redefinitions in
the graph as part of this change, so I'll leave it as is.

However, it does point out a bug in this code: it does not properly handle
redefinitions of redefinitions and nothing prevents them from arising.

+  // Remove redefinition instructions inserted to inhibit hoisting.
+  for (BlockIterator block_it = reverse_postorder_iterator();
+       !block_it.Done();
+       block_it.Advance()) {
+    for (ForwardInstructionIterator instr_it(block_it.Current());
+         !instr_it.Done();
+         instr_it.Advance()) {
+      RedefinitionInstr* redefinition = instr_it.Current()->AsRedefinition();
+      if (redefinition != NULL) {
+        redefinition->ReplaceUsesWith(redefinition->value()->definition());
+        instr_it.RemoveCurrentFromGraph();
+      }
+    }
+  }
+}
+
+
 // Find the natural loop for the back edge m->n and attach loop information
 // to block n (loop header). The algorithm is described in "Advanced Compiler
 // Design & Implementation" (Muchnick) p192.