Improve and fix constant propagation for type arguments.

runtime/vm/flow_graph_optimizer.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/flow_graph_optimizer.h"
 
 #include "vm/bit_vector.h"
 #include "vm/cha.h"
 #include "vm/flow_graph_builder.h"
 #include "vm/flow_graph_compiler.h"
@@ skipping 3529 matching lines @@
   SetValue(instr, instr->value()->definition()->constant_value());
 }
 
 
 void ConstantPropagator::VisitInstantiateTypeArguments(
     InstantiateTypeArgumentsInstr* instr) {
   const Object& object =
       instr->instantiator()->definition()->constant_value();
   if (IsNonConstant(object)) {
     SetValue(instr, non_constant_);
-  } else if (IsConstant(object)) {
-    if (!object.IsNull() &&
+    return;
+  }
+  if (IsConstant(object)) {
+    const intptr_t len = instr->type_arguments().Length();
+    if (instr->type_arguments().IsRawInstantiatedRaw(len) &&
+        object.IsNull()) {
+      SetValue(instr, object);
+      return;
+    }
+    if (instr->type_arguments().IsUninstantiatedIdentity() &&
+        !object.IsNull() &&
         object.IsTypeArguments() &&
-        (TypeArguments::Cast(object).Length() ==
-         instr->type_arguments().Length())) {
+        (TypeArguments::Cast(object).Length() == len)) {
       SetValue(instr, object);
-    } else {
-      SetValue(instr, non_constant_);
+      return;
     }
+    SetValue(instr, non_constant_);
   }
 }
 
 
 void ConstantPropagator::VisitExtractConstructorTypeArguments(
     ExtractConstructorTypeArgumentsInstr* instr) {
   SetValue(instr, non_constant_);
 }
 
 
@@ skipping 256 matching lines @@
     for (ForwardInstructionIterator i(block); !i.Done(); i.Advance()) {
       Definition* defn = i.Current()->AsDefinition();
       // Replace constant-valued instructions without observable side
       // effects.  Do this for smis only to avoid having to copy other
       // objects into the heap's old generation.
       //
       // TODO(kmillikin): Extend this to handle booleans, other number
       // types, etc.
       if ((defn != NULL) &&
           (defn->constant_value().IsSmi() ||
+           defn->constant_value().IsNull() ||
            defn->constant_value().IsTypeArguments()) &&
           !defn->IsConstant() &&
           !defn->IsPushArgument() &&
           !defn->IsStoreIndexed() &&
           !defn->IsStoreInstanceField() &&
           !defn->IsStoreStaticField() &&
           !defn->IsStoreVMField()) {
         if (FLAG_trace_constant_propagation) {
           OS::Print("Constant v%"Pd" = %s\n",
                     defn->ssa_temp_index(),
@@ skipping 61 matching lines @@
 
   if (FLAG_trace_constant_propagation) {
     OS::Print("\n==== After constant propagation ====\n");
     FlowGraphPrinter printer(*graph_);
     printer.PrintBlocks();
   }
 }
 
 
 }  // namespace dart