Implement a variation of scalar replacement for non-escaping allocations.

runtime/vm/object.h

 // 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.
 
 #ifndef VM_OBJECT_H_
 #define VM_OBJECT_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/utils.h"
@@ skipping 2578 matching lines @@
   // for a function. This value is used to catch potentially
   // malicious code.
   static const intptr_t kMaxHandlers = 1024 * 1024;
 
   void set_handled_types_data(const Array& value) const;
   FINAL_HEAP_OBJECT_IMPLEMENTATION(ExceptionHandlers, Object);
   friend class Class;
 };
 
 
-// Holds deopt information at one deoptimization point. The information
-// is a list of DeoptInstr objects, specifying transformation information
-// for each slot in unoptimized frame(s).
+// Holds deopt information at one deoptimization point. The information consists
+// of two parts:
+//  - first a prefix consiting of kMaterializeObject instructions describing
+//    objects which had their allocation removed as part of AllocationSinking
+//    pass and have to be materialized;
+//  - followed by a list of DeoptInstr objects, specifying transformation
+//    information for each slot in unoptimized frame(s).
+// Arguments for object materialization (class of instance to be allocated and
+// field-value pairs) are added as artificial slots to the expression stack
+// of the bottom-most frame. They are removed from the stack at the very end
+// of deoptimization by the deoptimization stub.
 class DeoptInfo : public Object {
  private:
   // Describes the layout of deopt info data. The index of a deopt-info entry
   // is implicitly the target slot in which the value is written into.
   enum {
     kInstruction = 0,
     kFromIndex,
     kNumberOfEntries,
   };
 
  public:
   // The number of instructions.
   intptr_t Length() const;
 
   // The number of real (non-suffix) instructions needed to execute the
   // deoptimization translation.
   intptr_t TranslationLength() const;
 
+  // Size of the frame part of the translation not counting kMaterializeObject
+  // instructions in the prefix.
+  intptr_t FrameSize() const;
+
   static RawDeoptInfo* New(intptr_t num_commands);
 
   static const intptr_t kBytesPerElement = (kNumberOfEntries * kWordSize);
   static const intptr_t kMaxElements = kSmiMax / kBytesPerElement;
 
   static intptr_t InstanceSize() {
     ASSERT(sizeof(RawDeoptInfo) == OFFSET_OF(RawDeoptInfo, data_));
     return 0;
   }
 
@@ skipping 3096 matching lines @@
 
 
 RawObject* MegamorphicCache::GetTargetFunction(const Array& array,
                                                intptr_t index) {
   return array.At((index * kEntryLength) + kTargetFunctionIndex);
 }
 
 }  // namespace dart
 
 #endif  // VM_OBJECT_H_