New linear scan allocator.

runtime/vm/locations.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_LOCATIONS_H_
 #define VM_LOCATIONS_H_
 
 #include "vm/allocation.h"
 #include "vm/assembler.h"
 #include "vm/bitfield.h"
@@ skipping 60 matching lines @@
     ASSERT(&obj == &loc.constant());
     return loc;
   }
 
   const Object& constant() const {
     ASSERT(IsConstant());
     return *reinterpret_cast<const Object*>(value_ & ~kConstantMask);
   }
 
   // Unallocated locations.
+  // TODO(vegorov): writable register policy?
   enum Policy {
+    kAny,
+    kPrefersRegister,
     kRequiresRegister,
     kSameAsFirstInput,
   };
 
   bool IsUnallocated() const {
     return kind() == kUnallocated;
   }
 
+  bool IsRegisterBeneficial() {
+    return !Equals(Any());
+  }
+
   static Location UnallocatedLocation(Policy policy) {
     return Location(kUnallocated, PolicyField::encode(policy));
   }
 
   // Any free register is suitable to replace this unallocated location.
+  static Location Any() {
+    return UnallocatedLocation(kAny);
+  }
+
+  static Location PrefersRegister() {
+    return UnallocatedLocation(kPrefersRegister);
+  }
+
   static Location RequiresRegister() {
     return UnallocatedLocation(kRequiresRegister);
   }
 
   // The location of the first input to the instruction will be
   // used to replace this unallocated location.
   static Location SameAsFirstInput() {
     return UnallocatedLocation(kSameAsFirstInput);
   }
 
@@ skipping 31 matching lines @@
   }
 
   intptr_t spill_index() const {
     ASSERT(IsSpillSlot());
     return static_cast<intptr_t>(payload());
   }
 
   const char* Name() const;
   void PrintTo(BufferFormatter* f) const;
 
-  // Compare two non-constant locations.
+  // Compare two locations.
   bool Equals(Location other) const {
-    ASSERT(!IsConstant() && !other.IsConstant());
     return value_ == other.value_;
   }
 
  private:
   explicit Location(uword value) : value_(value) { }
 
   Location(Kind kind, uword payload)
       : value_(KindField::encode(kind) | PayloadField::encode(payload)) { }
 
   uword payload() const {
     return PayloadField::decode(value_);
   }
 
   // If current location is constant might return something that
   // is not equal to any Kind.
   Kind kind() const {
     return KindField::decode(value_);
   }
 
   typedef BitField<Kind, 0, 3> KindField;
   typedef BitField<uword, 3, kWordSize * kBitsPerByte - 2> PayloadField;
 
   // Layout for kUnallocated locations payload.
-  typedef BitField<Policy, 0, 1> PolicyField;
+  typedef BitField<Policy, 0, 2> PolicyField;
 
   // Location either contains kind and payload fields or a tagged handle for
   // a constant locations. Values of enumeration Kind are selected in such a
   // way that none of them can be interpreted as a kConstant tag.
   uword value_;
 };
 
 
 // Specification of locations for inputs and output.
 class LocationSummary : public ZoneAllocated {
@@ skipping 69 matching lines @@
   GrowableArray<Location> temp_locations_;
   Location output_location_;
 
   const bool is_call_;
 };
 
 
 }  // namespace dart
 
 #endif  // VM_LOCATIONS_H_