[vm] Implement gradual refinement of types

runtime/vm/intermediate_language.h

 // 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.
 
 #ifndef RUNTIME_VM_INTERMEDIATE_LANGUAGE_H_
 #define RUNTIME_VM_INTERMEDIATE_LANGUAGE_H_
 
 #include "vm/allocation.h"
 #include "vm/ast.h"
 #include "vm/flags.h"
@@ skipping 131 matching lines @@
 
   // Create non-nullable Smi type.
   static CompileType Smi();
 
   // Create non-nullable String type.
   static CompileType String();
 
   // Perform a join operation over the type lattice.
   void Union(CompileType* other);
 
+  // Refine old type with newly inferred type (it could be more or less
+  // specific, or even unrelated to an old type in case of unreachable code).
+  // May return 'old_type', 'new_type' or create a new CompileType instance.
+  static CompileType* ComputeRefinedType(CompileType* old_type,
+                                         CompileType* new_type);
+
   // Returns true if this and other types are the same.
   bool IsEqualTo(CompileType* other) {
     return (is_nullable_ == other->is_nullable_) &&
            (ToNullableCid() == other->ToNullableCid()) &&
            (ToAbstractType()->Equals(*other->ToAbstractType()));
   }
 
   bool IsNone() const { return (cid_ == kIllegalCid) && (type_ == NULL); }
 
   bool IsInt() {
@@ skipping 65 matching lines @@
 
   static void AddToList(Value* value, Value** list);
   void RemoveFromUseList();
 
   // Change the definition after use lists have been computed.
   inline void BindTo(Definition* definition);
   inline void BindToEnvironment(Definition* definition);
 
   Value* Copy(Zone* zone) { return new (zone) Value(definition_); }
 
-  // This function must only be used when the new Value is dominated by
+  // CopyWithType() must only be used when the new Value is dominated by
   // the original Value.
-  Value* CopyWithType() {
-    Value* copy = new Value(definition_);
+  Value* CopyWithType(Zone* zone) {
+    Value* copy = new (zone) Value(definition_);
     copy->reaching_type_ = reaching_type_;
     return copy;
   }
+  Value* CopyWithType() { return CopyWithType(Thread::Current()->zone()); }
 
   CompileType* Type();
 
   void SetReachingType(CompileType* type) { reaching_type_ = type; }
+  void RefineReachingType(CompileType* type);
 
   void PrintTo(BufferFormatter* f) const;
 
   const char* ToCString() const;
 
   bool IsSmiValue() { return Type()->ToCid() == kSmiCid; }
 
   // Return true if the value represents a constant.
   bool BindsToConstant() const;
 
@@ skipping 7797 matching lines @@
 #define DEFINE_UNIMPLEMENTED_INSTRUCTION(Name)                                 \
   LocationSummary* Name::MakeLocationSummary(Zone* zone, bool opt) const {     \
     UNIMPLEMENTED();                                                           \
     return NULL;                                                               \
   }                                                                            \
   void Name::EmitNativeCode(FlowGraphCompiler* compiler) { UNIMPLEMENTED(); }
 
 }  // namespace dart
 
 #endif  // RUNTIME_VM_INTERMEDIATE_LANGUAGE_H_