Improve constant propagation for type arguments.

runtime/vm/flow_graph_optimizer.cc

 // Copyright (c) 2013, 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/dart_entry.h"
 #include "vm/flow_graph_builder.h"
@@ skipping 7218 matching lines @@
       SetValue(instr, object);
       return;
     }
     SetValue(instr, non_constant_);
   }
 }
 
 
 void ConstantPropagator::VisitExtractConstructorTypeArguments(
     ExtractConstructorTypeArgumentsInstr* instr) {
+  CompileType* type = instr->instantiator()->Type();
+  if (type->HasDecidableNullability()) {
+    if (!type->is_nullable()) {
+      SetValue(instr, instr->type_arguments());
+      return;
+    }
+    ASSERT(type->IsNull());
+    SetValue(instr, instr->instantiator()->definition()->constant_value());
+    return;
+  }
   SetValue(instr, non_constant_);
 }
 
 
 void ConstantPropagator::VisitExtractConstructorInstantiator(
     ExtractConstructorInstantiatorInstr* instr) {
+  CompileType* type = instr->instantiator()->Type();
+  if (type->HasDecidableNullability()) {
+    if (type->IsNull()) {
+      SetValue(instr, Smi::ZoneHandle(Smi::New(StubCode::kNoInstantiator)));
+      return;
+    }
+    ASSERT(!type->is_nullable());
+    SetValue(instr, instr->instantiator()->definition()->constant_value());
+    return;
+  }
   SetValue(instr, non_constant_);
 }
 
 
 void ConstantPropagator::VisitAllocateContext(AllocateContextInstr* instr) {
   SetValue(instr, non_constant_);
 }
 
 
 void ConstantPropagator::VisitCloneContext(CloneContextInstr* instr) {
@@ skipping 1225 matching lines @@
   }
 
   // Insert materializations at environment uses.
   for (intptr_t i = 0; i < exits.length(); i++) {
     CreateMaterializationAt(exits[i], alloc, alloc->cls(), *fields);
   }
 }
 
 
 }  // namespace dart