Trace CHA optimizations (where, when, why)

runtime/vm/flow_graph_type_propagator.cc

Index: runtime/vm/flow_graph_type_propagator.cc
diff --git a/runtime/vm/flow_graph_type_propagator.cc b/runtime/vm/flow_graph_type_propagator.cc
index 6fcd8742810a6c0c34c74da5a31903bb2f6ad781..f0ac5a6a530f8d27b4b085cf4758efb9dbc6e461 100644
--- a/runtime/vm/flow_graph_type_propagator.cc
+++ b/runtime/vm/flow_graph_type_propagator.cc
@@ -15,6 +15,7 @@ DEFINE_FLAG(bool, trace_type_propagation, false,
             "Trace flow graph type propagation");
 
 DECLARE_FLAG(bool, propagate_types);
+DECLARE_FLAG(bool, trace_cha);
 DECLARE_FLAG(bool, use_cha_deopt);
 
 
@@ -549,6 +550,10 @@ intptr_t CompileType::ToNullableCid() {
           // Type of a private class cannot change through later loaded libs.
           cid_ = type_class.id();
         } else if (FLAG_use_cha_deopt) {
+          if (FLAG_trace_cha) {
+            ISL_Print("  **(CHA) Compile type not subclassed: %s\n",
+                type_class.ToCString());
+          }
           cha->AddToLeafClasses(type_class);
           cid_ = type_class.id();
         } else {
@@ -786,6 +791,11 @@ CompileType ParameterInstr::ComputeType() const {
           cid = type_class.id();
         } else {
           if (FLAG_use_cha_deopt) {
+            if (FLAG_trace_cha) {
+              ISL_Print("  **(CHA) Computing exact type of parameters, "
+                  "no subclasses: %s\n",
+                  type_class.ToCString());
+            }
             thread->cha()->AddToLeafClasses(type_class);
             cid = type_class.id();
           }