[turbofan] remove checks for virtual register overflow

src/compiler/instruction.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILER_INSTRUCTION_H_
 #define V8_COMPILER_INSTRUCTION_H_
 
 #include <deque>
 #include <iosfwd>
 #include <map>
@@ skipping 55 matching lines @@
     value_ = KindField::encode(kind);
     value_ |= bit_cast<unsigned>(index << KindField::kSize);
     DCHECK(this->index() == index);
   }
 
   // Calls SetUpCache()/TearDownCache() for each subclass.
   static void SetUpCaches();
   static void TearDownCaches();
 
  protected:
-  typedef BitField64<Kind, 0, 3> KindField;
+  typedef BitField<Kind, 0, 3> KindField;
 
-  uint64_t value_;
+  uint32_t value_;
 };
 
 typedef ZoneVector<InstructionOperand*> InstructionOperandVector;
 
 struct PrintableInstructionOperand {
   const RegisterConfiguration* register_configuration_;
   const InstructionOperand* op_;
 };
 
 std::ostream& operator<<(std::ostream& os,
@@ skipping 19 matching lines @@
     // to some other operand used inside instruction (i.e. temporary or
     // output).
     USED_AT_START,
 
     // USED_AT_END operand is treated as live until the end of
     // instruction. This means that register allocator will not reuse it's
     // register for any other operand inside instruction.
     USED_AT_END
   };
 
+  static const int kInvalidVirtualRegister = -1;
+
   explicit UnallocatedOperand(ExtendedPolicy policy)
-      : InstructionOperand(UNALLOCATED, 0) {
-    value_ |= VirtualRegisterField::encode(kInvalidVirtualRegister);
+      : InstructionOperand(UNALLOCATED, 0),
+        virtual_register_(kInvalidVirtualRegister) {
     value_ |= BasicPolicyField::encode(EXTENDED_POLICY);
     value_ |= ExtendedPolicyField::encode(policy);
     value_ |= LifetimeField::encode(USED_AT_END);
   }
 
   UnallocatedOperand(BasicPolicy policy, int index)
-      : InstructionOperand(UNALLOCATED, 0) {
+      : InstructionOperand(UNALLOCATED, 0),
+        virtual_register_(kInvalidVirtualRegister) {
     DCHECK(policy == FIXED_SLOT);
-    value_ |= VirtualRegisterField::encode(kInvalidVirtualRegister);
     value_ |= BasicPolicyField::encode(policy);
-    value_ |= static_cast<int64_t>(index) << FixedSlotIndexField::kShift;
+    value_ |= static_cast<int32_t>(index) << FixedSlotIndexField::kShift;
     DCHECK(this->fixed_slot_index() == index);
   }
 
   UnallocatedOperand(ExtendedPolicy policy, int index)
-      : InstructionOperand(UNALLOCATED, 0) {
+      : InstructionOperand(UNALLOCATED, 0),
+        virtual_register_(kInvalidVirtualRegister) {
     DCHECK(policy == FIXED_REGISTER || policy == FIXED_DOUBLE_REGISTER);
-    value_ |= VirtualRegisterField::encode(kInvalidVirtualRegister);
     value_ |= BasicPolicyField::encode(EXTENDED_POLICY);
     value_ |= ExtendedPolicyField::encode(policy);
     value_ |= LifetimeField::encode(USED_AT_END);
     value_ |= FixedRegisterField::encode(index);
   }
 
   UnallocatedOperand(ExtendedPolicy policy, Lifetime lifetime)
-      : InstructionOperand(UNALLOCATED, 0) {
-    value_ |= VirtualRegisterField::encode(kInvalidVirtualRegister);
+      : InstructionOperand(UNALLOCATED, 0),
+        virtual_register_(kInvalidVirtualRegister) {
     value_ |= BasicPolicyField::encode(EXTENDED_POLICY);
     value_ |= ExtendedPolicyField::encode(policy);
     value_ |= LifetimeField::encode(lifetime);
   }
 
   UnallocatedOperand* CopyUnconstrained(Zone* zone) {
     UnallocatedOperand* result = new (zone) UnallocatedOperand(ANY);
     result->set_virtual_register(virtual_register());
     return result;
   }
 
   static const UnallocatedOperand* cast(const InstructionOperand* op) {
     DCHECK(op->IsUnallocated());
     return static_cast<const UnallocatedOperand*>(op);
   }
 
   static UnallocatedOperand* cast(InstructionOperand* op) {
     DCHECK(op->IsUnallocated());
     return static_cast<UnallocatedOperand*>(op);
   }
 
   // The encoding used for UnallocatedOperand operands depends on the policy
   // that is
   // stored within the operand. The FIXED_SLOT policy uses a compact encoding
   // because it accommodates a larger pay-load.
   //
   // For FIXED_SLOT policy:
-  //     +------------------------------------------+
-  //     |       slot_index      |  vreg  | 0 | 001 |
-  //     +------------------------------------------+
+  //     +-----------------------------+
+  //     |      slot_index   | 0 | 001 |
+  //     +-----------------------------+
   //
   // For all other (extended) policies:
-  //     +------------------------------------------+
-  //     |  reg_index  | L | PPP |  vreg  | 1 | 001 |    L ... Lifetime
-  //     +------------------------------------------+    P ... Policy
+  //     +----------------------------------+
+  //     |  reg_index  | L | PPP |  1 | 001 |    L ... Lifetime
+  //     +----------------------------------+    P ... Policy
   //
   // The slot index is a signed value which requires us to decode it manually
-  // instead of using the BitField64 utility class.
+  // instead of using the BitField utility class.
 
   // The superclass has a KindField.
   STATIC_ASSERT(KindField::kSize == 3);
 
   // BitFields for all unallocated operands.
-  class BasicPolicyField : public BitField64<BasicPolicy, 3, 1> {};
-  class VirtualRegisterField : public BitField64<unsigned, 4, 30> {};
+  class BasicPolicyField : public BitField<BasicPolicy, 3, 1> {};
 
   // BitFields specific to BasicPolicy::FIXED_SLOT.
-  class FixedSlotIndexField : public BitField64<int, 34, 30> {};
+  class FixedSlotIndexField : public BitField<int, 4, 28> {};
 
   // BitFields specific to BasicPolicy::EXTENDED_POLICY.
-  class ExtendedPolicyField : public BitField64<ExtendedPolicy, 34, 3> {};
-  class LifetimeField : public BitField64<Lifetime, 37, 1> {};
-  class FixedRegisterField : public BitField64<int, 38, 6> {};
+  class ExtendedPolicyField : public BitField<ExtendedPolicy, 4, 3> {};
+  class LifetimeField : public BitField<Lifetime, 7, 1> {};
+  class FixedRegisterField : public BitField<int, 8, 6> {};
 
-  static const int kInvalidVirtualRegister = VirtualRegisterField::kMax;
-  static const int kMaxVirtualRegisters = VirtualRegisterField::kMax;
   static const int kFixedSlotIndexWidth = FixedSlotIndexField::kSize;
   static const int kMaxFixedSlotIndex = (1 << (kFixedSlotIndexWidth - 1)) - 1;
   static const int kMinFixedSlotIndex = -(1 << (kFixedSlotIndexWidth - 1));
 
   // Predicates for the operand policy.
   bool HasAnyPolicy() const {
     return basic_policy() == EXTENDED_POLICY && extended_policy() == ANY;
   }
   bool HasFixedPolicy() const {
     return basic_policy() == FIXED_SLOT ||
@@ skipping 23 matching lines @@
 
   // [extended_policy]: Only for non-FIXED_SLOT. The finer-grained policy.
   ExtendedPolicy extended_policy() const {
     DCHECK(basic_policy() == EXTENDED_POLICY);
     return ExtendedPolicyField::decode(value_);
   }
 
   // [fixed_slot_index]: Only for FIXED_SLOT.
   int fixed_slot_index() const {
     DCHECK(HasFixedSlotPolicy());
-    return static_cast<int>(bit_cast<int64_t>(value_) >>
+    return static_cast<int>(bit_cast<int32_t>(value_) >>
                             FixedSlotIndexField::kShift);
   }
 
   // [fixed_register_index]: Only for FIXED_REGISTER or FIXED_DOUBLE_REGISTER.
   int fixed_register_index() const {
     DCHECK(HasFixedRegisterPolicy() || HasFixedDoubleRegisterPolicy());
     return FixedRegisterField::decode(value_);
   }
 
+  // TODO(dcarney): return unsigned or make virtual register opaque.
   // [virtual_register]: The virtual register ID for this operand.
-  int virtual_register() const { return VirtualRegisterField::decode(value_); }
+  int virtual_register() const { return virtual_register_; }

[Benedikt Meurer, 2015/01/07 11:24:08]

Can't we just change the return type to unsigned here, and make the field itself
unsigned?

   void set_virtual_register(unsigned id) {
-    value_ = VirtualRegisterField::update(value_, id);
+    virtual_register_ = static_cast<int>(id);
   }
 
   // [lifetime]: Only for non-FIXED_SLOT.
   bool IsUsedAtStart() const {
     DCHECK(basic_policy() == EXTENDED_POLICY);
     return LifetimeField::decode(value_) == USED_AT_START;
   }
+
+ private:
+  int32_t virtual_register_;
 };
 
 
 class MoveOperands FINAL {
  public:
   MoveOperands(InstructionOperand* source, InstructionOperand* destination)
       : source_(source), destination_(destination) {}
 
   InstructionOperand* source() const { return source_; }
   void set_source(InstructionOperand* operand) { source_ = operand; }
@@ skipping 662 matching lines @@
 // TODO(titzer): s/IsDouble/IsFloat64/
 class InstructionSequence FINAL : public ZoneObject {
  public:
   static InstructionBlocks* InstructionBlocksFor(Zone* zone,
                                                  const Schedule* schedule);
   // Puts the deferred blocks last.
   static void ComputeAssemblyOrder(InstructionBlocks* blocks);
 
   InstructionSequence(Zone* zone, InstructionBlocks* instruction_blocks);
 
-  int NextVirtualRegister() { return next_virtual_register_++; }
+  int NextVirtualRegister();
   int VirtualRegisterCount() const { return next_virtual_register_; }
 
   const InstructionBlocks& instruction_blocks() const {
     return *instruction_blocks_;
   }
 
   int InstructionBlockCount() const {
     return static_cast<int>(instruction_blocks_->size());
   }
 
@@ skipping 126 matching lines @@
 
 
 std::ostream& operator<<(std::ostream& os,
                          const PrintableInstructionSequence& code);
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_INSTRUCTION_H_