[turbofan] Introduce dedicated CallFrequency class.

src/compiler/js-operator.h

Index: src/compiler/js-operator.h
diff --git a/src/compiler/js-operator.h b/src/compiler/js-operator.h
index cb49ce4a40cd5747ff0241d5a5ffa5c16cfccd02..4142a2b261f95e72dba6ce3ce51181e3e4ecb925 100644
--- a/src/compiler/js-operator.h
+++ b/src/compiler/js-operator.h
@@ -26,6 +26,37 @@ namespace compiler {
 class Operator;
 struct JSOperatorGlobalCache;
 
+// Defines the frequency a given Call/Construct site was executed. For some
+// call sites the frequency is not known.
+class CallFrequency final {
+ public:
+  CallFrequency() : value_(std::numeric_limits<float>::quiet_NaN()) {}
+  explicit CallFrequency(float value) : value_(value) {
+    DCHECK(!std::isnan(value));
+  }
+
+  bool IsKnown() const { return !IsUnknown(); }
+  bool IsUnknown() const { return std::isnan(value_); }
+  float value() const {
+    DCHECK(IsKnown());
+    return value_;
+  }
+
+  bool operator==(CallFrequency const& that) const {
+    return bit_cast<uint32_t>(this->value_) == bit_cast<uint32_t>(that.value_);
+  }
+  bool operator!=(CallFrequency const& that) const { return !(*this == that); }
+
+  friend size_t hash_value(CallFrequency f) {
+    return bit_cast<uint32_t>(f.value_);
+  }
+
+ private:
+  float value_;
+};
+
+std::ostream& operator<<(std::ostream&, CallFrequency);
+
 // Defines a pair of {FeedbackVector} and {FeedbackSlot}, which
 // is used to access the type feedback for a certain {Node}.
 class V8_EXPORT_PRIVATE VectorSlotPair {
@@ -64,17 +95,17 @@ ToBooleanHints ToBooleanHintsOf(Operator const* op);
 // used as a parameter by JSConstruct operators.
 class ConstructParameters final {
  public:
-  ConstructParameters(uint32_t arity, float frequency,
+  ConstructParameters(uint32_t arity, CallFrequency frequency,
                       VectorSlotPair const& feedback)
       : arity_(arity), frequency_(frequency), feedback_(feedback) {}
 
   uint32_t arity() const { return arity_; }
-  float frequency() const { return frequency_; }
+  CallFrequency frequency() const { return frequency_; }
   VectorSlotPair const& feedback() const { return feedback_; }
 
  private:
   uint32_t const arity_;
-  float const frequency_;
+  CallFrequency const frequency_;
   VectorSlotPair const feedback_;
 };
 
@@ -152,8 +183,9 @@ CallForwardVarargsParameters const& CallForwardVarargsParametersOf(
 // used as a parameter by JSCall operators.
 class CallParameters final {
  public:
-  CallParameters(size_t arity, float frequency, VectorSlotPair const& feedback,
-                 TailCallMode tail_call_mode, ConvertReceiverMode convert_mode)
+  CallParameters(size_t arity, CallFrequency frequency,
+                 VectorSlotPair const& feedback, TailCallMode tail_call_mode,
+                 ConvertReceiverMode convert_mode)
       : bit_field_(ArityField::encode(arity) |
                    ConvertReceiverModeField::encode(convert_mode) |
                    TailCallModeField::encode(tail_call_mode)),
@@ -161,7 +193,7 @@ class CallParameters final {
         feedback_(feedback) {}
 
   size_t arity() const { return ArityField::decode(bit_field_); }
-  float frequency() const { return frequency_; }
+  CallFrequency frequency() const { return frequency_; }
   ConvertReceiverMode convert_mode() const {
     return ConvertReceiverModeField::decode(bit_field_);
   }
@@ -187,7 +219,7 @@ class CallParameters final {
   typedef BitField<TailCallMode, 31, 1> TailCallModeField;
 
   uint32_t const bit_field_;
-  float const frequency_;
+  CallFrequency const frequency_;
   VectorSlotPair const feedback_;
 };
 
@@ -636,7 +668,7 @@ class V8_EXPORT_PRIVATE JSOperatorBuilder final
   const Operator* CallForwardVarargs(uint32_t start_index,
                                      TailCallMode tail_call_mode);
   const Operator* Call(
-      size_t arity, float frequency = 0.0f,
+      size_t arity, CallFrequency frequency = CallFrequency(),
       VectorSlotPair const& feedback = VectorSlotPair(),
       ConvertReceiverMode convert_mode = ConvertReceiverMode::kAny,
       TailCallMode tail_call_mode = TailCallMode::kDisallow);
@@ -644,8 +676,9 @@ class V8_EXPORT_PRIVATE JSOperatorBuilder final
   const Operator* CallRuntime(Runtime::FunctionId id);
   const Operator* CallRuntime(Runtime::FunctionId id, size_t arity);
   const Operator* CallRuntime(const Runtime::Function* function, size_t arity);
-  const Operator* Construct(uint32_t arity, float frequency,
-                            VectorSlotPair const& feedback);
+  const Operator* Construct(uint32_t arity,
+                            CallFrequency frequency = CallFrequency(),
+                            VectorSlotPair const& feedback = VectorSlotPair());
   const Operator* ConstructWithSpread(uint32_t arity);
 
   const Operator* ConvertReceiver(ConvertReceiverMode convert_mode);