Weight variables by their number of uses for register allocation.

src/IceOperand.h

Index: src/IceOperand.h
diff --git a/src/IceOperand.h b/src/IceOperand.h
index bcb38d03d395191d04ebc24a675e957d3df39bba..a2593ea654e3678d4bf00d23936b21a2c51873fc 100644
--- a/src/IceOperand.h
+++ b/src/IceOperand.h
@@ -332,8 +332,6 @@ public:
   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;
@@ -346,9 +344,7 @@ 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;
@@ -364,7 +360,6 @@ public:
 
   void reset() {
     Range.clear();
-    Weight.setWeight(0);
     untrim();
   }
   void addSegment(InstNumberT Start, InstNumberT End);
@@ -384,9 +379,6 @@ public:
   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:
@@ -395,7 +387,6 @@ private:
   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
@@ -417,6 +408,12 @@ class Variable : public Operand {
   Variable(const Variable &) = delete;
   Variable &operator=(const Variable &) = delete;
 
+  enum RegRequirement {
+    ShouldHaveRegister,
+    MustHaveRegister,
+    MustNotHaveRegister,
+  };
+
 public:
   static Variable *create(Cfg *Func, Type Ty, SizeT Index) {
     return new (Func->allocate<Variable>()) Variable(kVariable, Ty, Index);
@@ -454,25 +451,29 @@ public:
   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 Weight) { Weight += Weight; }

[jvoung (off chromium), 2015/08/26 22:35:16]

I'm a bit worried about the variable shadowing here (Weight += Weight)?

[ascull, 2015/08/26 22:53:49]

Done.

+
+  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(); }
@@ -540,7 +541,11 @@ protected:
   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