InstructionCost.h

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//===- InstructionCost.h ----------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
/// \file
/// This file defines an InstructionCost class that is used when calculating
/// the cost of an instruction, or a group of instructions. In addition to a
/// numeric value representing the cost the class also contains a state that
/// can be used to encode particular properties, such as a cost being invalid.
/// Operations on InstructionCost implement saturation arithmetic, so that
/// accumulating costs on large cost-values don't overflow.
///
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_SUPPORT_INSTRUCTIONCOST_H
#define LLVM_SUPPORT_INSTRUCTIONCOST_H
 
#include "llvm/Support/MathExtras.h"
#include <limits>
#include <optional>
 
namespace llvm {
 
class raw_ostream;
 
class InstructionCost {
public:
  using CostType = int64_t;
 
  /// CostState describes the state of a cost.
  enum CostState {
    Valid,  /// < The cost value represents a valid cost, even when the
            /// cost-value is large.
    Invalid /// < Invalid indicates there is no way to represent the cost as a
            /// numeric value. This state exists to represent a possible issue,
            /// e.g. if the cost-model knows the operation cannot be expanded
            /// into a valid code-sequence by the code-generator.  While some
            /// passes may assert that the calculated cost must be valid, it is
            /// up to individual passes how to interpret an Invalid cost. For
            /// example, a transformation pass could choose not to perform a
            /// transformation if the resulting cost would end up Invalid.
            /// Because some passes may assert a cost is Valid, it is not
            /// recommended to use Invalid costs to model 'Unknown'.
            /// Note that Invalid is semantically different from a (very) high,
            /// but valid cost, which intentionally indicates no issue, but
            /// rather a strong preference not to select a certain operation.
  };
 
private:
  CostType Value = 0;
  CostState State = Valid;
 
  void propagateState(const InstructionCost &RHS) {
    if (RHS.State == Invalid)
      State = Invalid;
  }
 
  static CostType getMaxValue() { return std::numeric_limits<CostType>::max(); }
  static CostType getMinValue() { return std::numeric_limits<CostType>::min(); }
 
public:
  // A default constructed InstructionCost is a valid zero cost
  InstructionCost() = default;
 
  InstructionCost(CostState) = delete;
  InstructionCost(CostType Val) : Value(Val), State(Valid) {}
 
  static InstructionCost getMax() { return getMaxValue(); }
  static InstructionCost getMin() { return getMinValue(); }
  static InstructionCost getInvalid(CostType Val = 0) {
    InstructionCost Tmp(Val);
    Tmp.setInvalid();
    return Tmp;
  }
 
  bool isValid() const { return State == Valid; }
  void setValid() { State = Valid; }
  void setInvalid() { State = Invalid; }
  CostState getState() const { return State; }
 
  /// This function is intended to be used as sparingly as possible, since the
  /// class provides the full range of operator support required for arithmetic
  /// and comparisons.
  std::optional<CostType> getValue() const {
    if (isValid())
      return Value;
    return std::nullopt;
  }
 
  /// For all of the arithmetic operators provided here any invalid state is
  /// perpetuated and cannot be removed. Once a cost becomes invalid it stays
  /// invalid, and it also inherits any invalid state from the RHS.
  /// Arithmetic work on the actual values is implemented with saturation,
  /// to avoid overflow when using more extreme cost values.
 
  InstructionCost &operator+=(const InstructionCost &RHS) {
    propagateState(RHS);
 
    // Saturating addition.
    InstructionCost::CostType Result;
    if (AddOverflow(Value, RHS.Value, Result))
      Result = RHS.Value > 0 ? getMaxValue() : getMinValue();
 
    Value = Result;
    return *this;
  }
 
  InstructionCost &operator+=(const CostType RHS) {
    InstructionCost RHS2(RHS);
    *this += RHS2;
    return *this;
  }
 
  InstructionCost &operator-=(const InstructionCost &RHS) {
    propagateState(RHS);
 
    // Saturating subtract.
    InstructionCost::CostType Result;
    if (SubOverflow(Value, RHS.Value, Result))
      Result = RHS.Value > 0 ? getMinValue() : getMaxValue();
    Value = Result;
    return *this;
  }
 
  InstructionCost &operator-=(const CostType RHS) {
    InstructionCost RHS2(RHS);
    *this -= RHS2;
    return *this;
  }
 
  InstructionCost &operator*=(const InstructionCost &RHS) {
    propagateState(RHS);
 
    // Saturating multiply.
    InstructionCost::CostType Result;
    if (MulOverflow(Value, RHS.Value, Result)) {
      if ((Value > 0 && RHS.Value > 0) || (Value < 0 && RHS.Value < 0))
        Result = getMaxValue();
      else
        Result = getMinValue();
    }
 
    Value = Result;
    return *this;
  }
 
  InstructionCost &operator*=(const CostType RHS) {
    InstructionCost RHS2(RHS);
    *this *= RHS2;
    return *this;
  }
 
  InstructionCost &operator/=(const InstructionCost &RHS) {
    propagateState(RHS);
    Value /= RHS.Value;
    return *this;
  }
 
  InstructionCost &operator/=(const CostType RHS) {
    InstructionCost RHS2(RHS);
    *this /= RHS2;
    return *this;
  }
 
  InstructionCost &operator++() {
    *this += 1;
    return *this;
  }
 
  InstructionCost operator++(int) {
    InstructionCost Copy = *this;
    ++*this;
    return Copy;
  }
 
  InstructionCost &operator--() {
    *this -= 1;
    return *this;
  }
 
  InstructionCost operator--(int) {
    InstructionCost Copy = *this;
    --*this;
    return Copy;
  }
 
  /// For the comparison operators we have chosen to use lexicographical
  /// ordering where valid costs are always considered to be less than invalid
  /// costs. This avoids having to add asserts to the comparison operators that
  /// the states are valid and users can test for validity of the cost
  /// explicitly.
  bool operator<(const InstructionCost &RHS) const {
    if (State != RHS.State)
      return State < RHS.State;
    return Value < RHS.Value;
  }
 
  // Implement in terms of operator< to ensure that the two comparisons stay in
  // sync
  bool operator==(const InstructionCost &RHS) const {
    return !(*this < RHS) && !(RHS < *this);
  }
 
  bool operator!=(const InstructionCost &RHS) const { return !(*this == RHS); }
 
  bool operator==(const CostType RHS) const {
    InstructionCost RHS2(RHS);
    return *this == RHS2;
  }
 
  bool operator!=(const CostType RHS) const { return !(*this == RHS); }
 
  bool operator>(const InstructionCost &RHS) const { return RHS < *this; }
 
  bool operator<=(const InstructionCost &RHS) const { return !(RHS < *this); }
 
  bool operator>=(const InstructionCost &RHS) const { return !(*this < RHS); }
 
  bool operator<(const CostType RHS) const {
    InstructionCost RHS2(RHS);
    return *this < RHS2;
  }
 
  bool operator>(const CostType RHS) const {
    InstructionCost RHS2(RHS);
    return *this > RHS2;
  }
 
  bool operator<=(const CostType RHS) const {
    InstructionCost RHS2(RHS);
    return *this <= RHS2;
  }
 
  bool operator>=(const CostType RHS) const {
    InstructionCost RHS2(RHS);
    return *this >= RHS2;
  }
 
  void print(raw_ostream &OS) const;
 
  template <class Function>
  auto map(const Function &F) const -> InstructionCost {
    if (isValid())
      return F(Value);
    return getInvalid();
  }
};
 
inline InstructionCost operator+(const InstructionCost &LHS,
                                 const InstructionCost &RHS) {
  InstructionCost LHS2(LHS);
  LHS2 += RHS;
  return LHS2;
}
 
inline InstructionCost operator-(const InstructionCost &LHS,
                                 const InstructionCost &RHS) {
  InstructionCost LHS2(LHS);
  LHS2 -= RHS;
  return LHS2;
}
 
inline InstructionCost operator*(const InstructionCost &LHS,
                                 const InstructionCost &RHS) {
  InstructionCost LHS2(LHS);
  LHS2 *= RHS;
  return LHS2;
}
 
inline InstructionCost operator/(const InstructionCost &LHS,
                                 const InstructionCost &RHS) {
  InstructionCost LHS2(LHS);
  LHS2 /= RHS;
  return LHS2;
}
 
inline raw_ostream &operator<<(raw_ostream &OS, const InstructionCost &V) {
  V.print(OS);
  return OS;
}
 
} // namespace llvm
 
#endif