Skeleton of a linear scan register allocator.

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 a02a048f50c3c75d750092c4c44fcd1c185e0c58..8072c6abd77b8f58b29637caaa3033bc3fd7f1b4 100644
--- a/runtime/vm/flow_graph_optimizer.cc
+++ b/runtime/vm/flow_graph_optimizer.cc
@@ -527,6 +527,9 @@ void FlowGraphOptimizer::VisitStoreIndexed(StoreIndexedComp* comp,
 }
 
 
+#if 0
+// TODO(vegorov): land a separate CL to fix the fusion. Now it should remove
+// instruction from the graph to avoid confusing register allocator.
 static void TryFuseComparisonWithBranch(BindInstr* instr,
                                         ComparisonComp* comp) {
   Instruction* next_instr = instr->next();
@@ -558,6 +561,7 @@ static void TryFuseComparisonWithBranch(BindInstr* instr,
     }
   }
 }
+#endif
 
 
 void FlowGraphOptimizer::VisitRelationalOp(RelationalOpComp* comp,
@@ -581,13 +585,17 @@ void FlowGraphOptimizer::VisitRelationalOp(RelationalOpComp* comp,
   // For smi and double comparisons if the next instruction is a conditional
   // branch that uses the value of this comparison mark them as fused together
   // to avoid materializing a boolean value.
+#if 0

[srdjan, 2012/07/11 17:22:32]

Enable once synced with branch fusion fix

   TryFuseComparisonWithBranch(instr, comp);
+#endif
 }
 
 
 void FlowGraphOptimizer::VisitStrictCompare(StrictCompareComp* comp,
                                             BindInstr* instr) {
+#if 0
   TryFuseComparisonWithBranch(instr, comp);
+#endif
 }
 
 
@@ -600,7 +608,9 @@ void FlowGraphOptimizer::VisitEqualityCompare(EqualityCompareComp* comp,
     comp->set_ic_data(&unary_checks);
   }
 
+#if 0
   TryFuseComparisonWithBranch(instr, comp);
+#endif
 }