Add support for fixed parameters in the register 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 28 matching lines @@
     // a policy that specifies what kind of location is suitable. Payload
     // contains register allocation policy.
     kUnallocated = 2,
 
     // Register location represents a fixed register.  Payload contains
     // register code.
     kRegister = 3,
 
     // Spill slot allocated by the register allocator.  Payload contains
     // a spill index.
-    kSpillSlot = 4
+    kStackSlot = 4,
+  };
+
+  enum {
+    // Number of bits required to encode Kind value.
+    kBitsForKind = 3,
+    kBitsForPayload = kWordSize * kBitsPerByte - kBitsForKind
   };
 
   static const uword kInvalidLocation = 0;
   static const uword kConstantMask = 0x3;
 
   Location() : value_(kInvalidLocation) {
     ASSERT(IsInvalid());
   }
 
   bool IsInvalid() const {
@@ skipping 75 matching lines @@
   bool IsRegister() const {
     return kind() == kRegister;
   }
 
   Register reg() const {
     ASSERT(IsRegister());
     return static_cast<Register>(payload());
   }
 
   // Spill slots.
-  static Location SpillSlot(intptr_t spill_index) {
-    return Location(kSpillSlot, static_cast<uword>(spill_index));
+  static const intptr_t kStackIndexBias =
+      static_cast<intptr_t>(1) << (kBitsForPayload - 1);
+  static Location StackSlot(intptr_t stack_index) {
+    ASSERT((-kStackIndexBias <= stack_index) &&
+           (stack_index < kStackIndexBias));
+    Location loc(kStackSlot, static_cast<uword>(kStackIndexBias + stack_index));
+    // Ensure that sign is preserved.
+    ASSERT(loc.stack_index() == stack_index);
+    return loc;
   }
 
-  bool IsSpillSlot() const {
-    return kind() == kSpillSlot;
+  bool IsStackSlot() const {
+    return kind() == kStackSlot;
   }
 
-  intptr_t spill_index() const {
-    ASSERT(IsSpillSlot());
-    return static_cast<intptr_t>(payload());
+  intptr_t stack_index() const {
+    ASSERT(IsStackSlot());
+    // Decode stack index manually to preserve sign.
+    return payload() - kStackIndexBias;
   }
 
   const char* Name() const;
   void PrintTo(BufferFormatter* f) const;
 
   // Compare two locations.
   bool Equals(Location other) const {
     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;
+  typedef BitField<Kind, 0, kBitsForKind> KindField;
+  typedef BitField<uword, kBitsForKind, kBitsForPayload> PayloadField;
 
   // Layout for kUnallocated locations payload.
   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_;
 };
 
@@ skipping 75 matching lines @@
   GrowableArray<Location> temp_locations_;
   Location output_location_;
 
   const bool is_call_;
 };
 
 
 }  // namespace dart
 
 #endif  // VM_LOCATIONS_H_