Compute local variable liveness before translation to SSA.

runtime/vm/flow_graph_optimizer.cc

Index: runtime/vm/flow_graph_optimizer.cc
diff --git a/runtime/vm/flow_graph_optimizer.cc b/runtime/vm/flow_graph_optimizer.cc
index 9e6ee4efe41b9e45abc243c7dc5c4136ccd598a2..feceb41e84c967646934e1baa483a91d95383089 100644
--- a/runtime/vm/flow_graph_optimizer.cc
+++ b/runtime/vm/flow_graph_optimizer.cc
@@ -3252,7 +3252,7 @@ class LoadOptimizer : public ValueObject {
           for (intptr_t i = 0; i < block->PredecessorCount(); i++) {
             BlockEntryInstr* pred = block->PredecessorAt(i);
             BitVector* pred_out = out_[pred->preorder_number()];
-            temp->Intersect(*pred_out);
+            temp->Intersect(pred_out);
           }
         }
 
@@ -4435,6 +4435,8 @@ void ConstantPropagator::Transform() {
         // Replace the false target entry with the new join entry. We will
         // recompute the dominators after this pass.
         join->LinkTo(next);
+        jump->SetEnvironment(branch->env());

[Vyacheslav Egorov (Google), 2013/03/21 22:48:27]

This change revealed serious flaw in the way we restructure graph that slipped
past reviews before. 

We when we insert goto's into the graph we forget to attach the environment to
them... But we *must* do that goto can become a deoptimization target.

It is very fragile part of the system. Fix in this place extinguished immediate
fire but we need to review all places where we generate gotos and branches and
ensure that they get proper environment. 

[Kevin Millikin (Google), 2013/03/22 11:57:52]

I wouldn't say it's a flaw in the way we restructure the graph, but a flaw in
the way we record deoptimization environments.

Off the top of my head, there are two more occurrences in this file just below
for branch propagation, and occurrences also for inlining exits.

As we try to do more complicated things with changing the graph structure, this
will get harder and harder.

+        branch->SetEnvironment(NULL);
         branch->UnuseAllInputs();
       }
     }