With --noopt run unoptimized code through optimizer, more optimizations can be done later.

runtime/vm/block_scheduler.cc

Index: runtime/vm/block_scheduler.cc
diff --git a/runtime/vm/block_scheduler.cc b/runtime/vm/block_scheduler.cc
index f04aa9522d0fe9deb0e870a421bf9ddcaa56e64e..e8d950c536022cc616352c1dfaf08dc0db3ba651 100644
--- a/runtime/vm/block_scheduler.cc
+++ b/runtime/vm/block_scheduler.cc
@@ -80,6 +80,9 @@ static void SetEdgeWeight(Instruction* instruction,
 
 
 void BlockScheduler::AssignEdgeWeights() const {
+  if (!FLAG_emit_edge_counters) {
+    return;
+  }
   const Code& unoptimized_code = flow_graph()->parsed_function().code();
   ASSERT(!unoptimized_code.IsNull());