Weight variables by their number of uses for register allocation.

src/IceOperand.h

 //===- subzero/src/IceOperand.h - High-level operands -----------*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 314 matching lines @@
   const static uint32_t Zero = 0; /// Force regalloc NOT to give a register
   void addWeight(uint32_t Delta) {
     if (Delta == Inf)
       Weight = Inf;
     else if (Weight != Inf)
       Weight += Delta;
   }
   void addWeight(const RegWeight &Other) { addWeight(Other.Weight); }
   void setWeight(uint32_t Val) { Weight = Val; }
   uint32_t getWeight() const { return Weight; }
-  bool isInf() const { return Weight == Inf; }
-  bool isZero() const { return Weight == Zero; }
 
 private:
   uint32_t Weight = 0;
 };
 Ostream &operator<<(Ostream &Str, const RegWeight &W);
 bool operator<(const RegWeight &A, const RegWeight &B);
 bool operator<=(const RegWeight &A, const RegWeight &B);
 bool operator==(const RegWeight &A, const RegWeight &B);
 
 /// LiveRange is a set of instruction number intervals representing
 /// a variable's live range.  Generally there is one interval per basic
 /// block where the variable is live, but adjacent intervals get
-/// coalesced into a single interval.  LiveRange also includes a
-/// weight, in case e.g. we want a live range to have higher weight
-/// inside a loop.
+/// coalesced into a single interval.
 class LiveRange {
 public:
   LiveRange() = default;
   /// Special constructor for building a kill set.  The advantage is
   /// that we can reserve the right amount of space in advance.
   explicit LiveRange(const std::vector<InstNumberT> &Kills) {
     Range.reserve(Kills.size());
     for (InstNumberT I : Kills)
       addSegment(I, I);
   }
   LiveRange(const LiveRange &) = default;
   LiveRange &operator=(const LiveRange &) = default;
 
   void reset() {
     Range.clear();
-    Weight.setWeight(0);
     untrim();
   }
   void addSegment(InstNumberT Start, InstNumberT End);
 
   bool endsBefore(const LiveRange &Other) const;
   bool overlaps(const LiveRange &Other, bool UseTrimmed = false) const;
   bool overlapsInst(InstNumberT OtherBegin, bool UseTrimmed = false) const;
   bool containsValue(InstNumberT Value, bool IsDest) const;
   bool isEmpty() const { return Range.empty(); }
   InstNumberT getStart() const {
     return Range.empty() ? -1 : Range.begin()->first;
   }
   InstNumberT getEnd() const {
     return Range.empty() ? -1 : Range.rbegin()->second;
   }
 
   void untrim() { TrimmedBegin = Range.begin(); }
   void trim(InstNumberT Lower);
 
-  RegWeight getWeight() const { return Weight; }
-  void setWeight(const RegWeight &NewWeight) { Weight = NewWeight; }
-  void addWeight(uint32_t Delta) { Weight.addWeight(Delta); }
   void dump(Ostream &Str) const;
 
 private:
   typedef std::pair<InstNumberT, InstNumberT> RangeElementType;
   /// RangeType is arena-allocated from the Cfg's allocator.
   typedef std::vector<RangeElementType, CfgLocalAllocator<RangeElementType>>
       RangeType;
   RangeType Range;
-  RegWeight Weight = RegWeight(0);
   /// TrimmedBegin is an optimization for the overlaps() computation.
   /// Since the linear-scan algorithm always calls it as overlaps(Cur)
   /// and Cur advances monotonically according to live range start, we
   /// can optimize overlaps() by ignoring all segments that end before
   /// the start of Cur's range.  The linear-scan code enables this by
   /// calling trim() on the ranges of interest as Cur advances.  Note
   /// that linear-scan also has to initialize TrimmedBegin at the
   /// beginning by calling untrim().
   RangeType::const_iterator TrimmedBegin;
 };
 
 Ostream &operator<<(Ostream &Str, const LiveRange &L);
 
 /// Variable represents an operand that is register-allocated or
 /// stack-allocated.  If it is register-allocated, it will ultimately
 /// have a non-negative RegNum field.
 class Variable : public Operand {
   Variable() = delete;
   Variable(const Variable &) = delete;
   Variable &operator=(const Variable &) = delete;
 
+  enum RegRequirement {
+    ShouldHaveRegister,

[Jim Stichnoth, 2015/08/27 05:03:06]

I prefer to prefix enum values with some prefix, like RR_ .

Also, "Should" suggests something too strong here -- maybe MayHaveRegister or
NoRequirement ?

[ascull, 2015/08/28 19:26:36]

Done.

+    MustHaveRegister,
+    MustNotHaveRegister,
+  };
+
 public:
   static Variable *create(Cfg *Func, Type Ty, SizeT Index) {
     return new (Func->allocate<Variable>()) Variable(kVariable, Ty, Index);
   }
 
   SizeT getIndex() const { return Number; }
   IceString getName(const Cfg *Func) const;
   void setName(Cfg *Func, const IceString &NewName) {
     // Make sure that the name can only be set once.
     assert(NameIndex == Cfg::IdentifierIndexInvalid);
@@ skipping 17 matching lines @@
   int32_t getRegNum() const { return RegNum; }
   void setRegNum(int32_t NewRegNum) {
     // Regnum shouldn't be set more than once.
     assert(!hasReg() || RegNum == NewRegNum);
     RegNum = NewRegNum;
   }
   bool hasRegTmp() const { return getRegNumTmp() != NoRegister; }
   int32_t getRegNumTmp() const { return RegNumTmp; }
   void setRegNumTmp(int32_t NewRegNum) { RegNumTmp = NewRegNum; }
 
-  RegWeight getWeight() const { return Weight; }
-  void setWeight(uint32_t NewWeight) { Weight = RegWeight(NewWeight); }
-  void setWeightInfinite() { setWeight(RegWeight::Inf); }
+  RegWeight getWeight() const {
+    return RegWeight(mustHaveReg() ? RegWeight::Inf : mustNotHaveReg()
+                                                          ? RegWeight::Zero
+                                                          : Weight);
+  }
+  void resetUses() { Weight = 0; }
+  void addUse(uint32_t UseWeight) { Weight += UseWeight; }
+
+  void setMustHaveReg() { RegRequirement = MustHaveRegister; }
+  bool mustHaveReg() const { return RegRequirement == MustHaveRegister; }
+  void setMustNotHaveReg() { RegRequirement = MustNotHaveRegister; }
+  bool mustNotHaveReg() const { return RegRequirement == MustNotHaveRegister; }
 
   LiveRange &getLiveRange() { return Live; }
   const LiveRange &getLiveRange() const { return Live; }
   void setLiveRange(const LiveRange &Range) { Live = Range; }
-  void resetLiveRange() { Live.reset(); }
-  void addLiveRange(InstNumberT Start, InstNumberT End, uint32_t WeightDelta) {
+  void resetLiveRange() {
+    Live.reset();
+    resetUses();
+  }
+  void addLiveRange(InstNumberT Start, InstNumberT End) {
     assert(!getIgnoreLiveness());
-    assert(WeightDelta != RegWeight::Inf);
     Live.addSegment(Start, End);
-    if (Weight.isInf())
-      Live.setWeight(RegWeight(RegWeight::Inf));
-    else
-      Live.addWeight(WeightDelta * Weight.getWeight());
-  }
-  void setLiveRangeInfiniteWeight() {
-    Live.setWeight(RegWeight(RegWeight::Inf));
   }
   void trimLiveRange(InstNumberT Start) { Live.trim(Start); }
   void untrimLiveRange() { Live.untrim(); }
   bool rangeEndsBefore(const Variable *Other) const {
     return Live.endsBefore(Other->Live);
   }
   bool rangeOverlaps(const Variable *Other) const {
     const bool UseTrimmed = true;
     return Live.overlaps(Other->Live, UseTrimmed);
   }
@@ skipping 47 matching lines @@
   /// reserved for the stack pointer.
   bool IgnoreLiveness = false;
   /// StackOffset is the canonical location on stack (only if
   /// RegNum==NoRegister || IsArgument).
   int32_t StackOffset = 0;
   /// RegNum is the allocated register, or NoRegister if it isn't
   /// register-allocated.
   int32_t RegNum = NoRegister;
   /// RegNumTmp is the tentative assignment during register allocation.
   int32_t RegNumTmp = NoRegister;
-  RegWeight Weight = RegWeight(1); // Register allocation priority
+  /// \name Register allocation priority
+  /// @{
+  uint32_t Weight = 0; /// Calculated by use count and loop nest depth.
+  RegRequirement RegRequirement = ShouldHaveRegister;
+  /// @}
   LiveRange Live;
   // LoVar and HiVar are needed for lowering from 64 to 32 bits.  When
   // lowering from I64 to I32 on a 32-bit architecture, we split the
   // variable into two machine-size pieces.  LoVar is the low-order
   // machine-size portion, and HiVar is the remaining high-order
   // portion.  TODO: It's wasteful to penalize all variables on all
   // targets this way; use a sparser representation.  It's also
   // wasteful for a 64-bit target.
   Variable *LoVar = nullptr;
   Variable *HiVar = nullptr;
@@ skipping 102 matching lines @@
 private:
   const Cfg *Func;
   MetadataKind Kind;
   std::vector<VariableTracking> Metadata;
   const static InstDefList NoDefinitions;
 };
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICEOPERAND_H