MCInstrItineraries.h

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//===-- llvm/MC/MCInstrItineraries.h - Scheduling ---------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file describes the structures used for instruction
// itineraries, stages, and operand reads/writes.  This is used by
// schedulers to determine instruction stages and latencies.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_MC_MCINSTRITINERARIES_H
#define LLVM_MC_MCINSTRITINERARIES_H

#include "llvm/MC/MCSchedule.h"
#include <algorithm>

namespace llvm {

//===----------------------------------------------------------------------===//
/// Instruction stage - These values represent a non-pipelined step in
/// the execution of an instruction.  Cycles represents the number of
/// discrete time slots needed to complete the stage.  Units represent
/// the choice of functional units that can be used to complete the
/// stage.  Eg. IntUnit1, IntUnit2. NextCycles indicates how many
/// cycles should elapse from the start of this stage to the start of
/// the next stage in the itinerary. A value of -1 indicates that the
/// next stage should start immediately after the current one.
/// For example:
///
///   { 1, x, -1 }
///      indicates that the stage occupies FU x for 1 cycle and that
///      the next stage starts immediately after this one.
///
///   { 2, x|y, 1 }
///      indicates that the stage occupies either FU x or FU y for 2
///      consecuative cycles and that the next stage starts one cycle
///      after this stage starts. That is, the stage requirements
///      overlap in time.
///
///   { 1, x, 0 }
///      indicates that the stage occupies FU x for 1 cycle and that
///      the next stage starts in this same cycle. This can be used to
///      indicate that the instruction requires multiple stages at the
///      same time.
///
/// FU reservation can be of two different kinds:
///  - FUs which instruction actually requires
///  - FUs which instruction just reserves. Reserved unit is not available for
///    execution of other instruction. However, several instructions can reserve
///    the same unit several times.
/// Such two types of units reservation is used to model instruction domain
/// change stalls, FUs using the same resource (e.g. same register file), etc.

struct InstrStage {
  enum ReservationKinds {
    Required = 0,
    Reserved = 1
  };

  unsigned Cycles_;  ///< Length of stage in machine cycles
  unsigned Units_;   ///< Choice of functional units
  int NextCycles_;   ///< Number of machine cycles to next stage
  ReservationKinds Kind_; ///< Kind of the FU reservation

  /// getCycles - returns the number of cycles the stage is occupied
  unsigned getCycles() const {
    return Cycles_;
  }

  /// getUnits - returns the choice of FUs
  unsigned getUnits() const {
    return Units_;
  }

  ReservationKinds getReservationKind() const {
    return Kind_;
  }

  /// getNextCycles - returns the number of cycles from the start of
  /// this stage to the start of the next stage in the itinerary
  unsigned getNextCycles() const {
    return (NextCycles_ >= 0) ? (unsigned)NextCycles_ : Cycles_;
  }
};


//===----------------------------------------------------------------------===//
/// Instruction itinerary - An itinerary represents the scheduling
/// information for an instruction. This includes a set of stages
/// occupies by the instruction, and the pipeline cycle in which
/// operands are read and written.
///
struct InstrItinerary {
  int      NumMicroOps;        ///< # of micro-ops, -1 means it's variable
  unsigned FirstStage;         ///< Index of first stage in itinerary
  unsigned LastStage;          ///< Index of last + 1 stage in itinerary
  unsigned FirstOperandCycle;  ///< Index of first operand rd/wr
  unsigned LastOperandCycle;   ///< Index of last + 1 operand rd/wr
};


//===----------------------------------------------------------------------===//
/// Instruction itinerary Data - Itinerary data supplied by a subtarget to be
/// used by a target.
///
class InstrItineraryData {
public:
  MCSchedModel          SchedModel;     ///< Basic machine properties.
  const InstrStage     *Stages;         ///< Array of stages selected
  const unsigned       *OperandCycles;  ///< Array of operand cycles selected
  const unsigned       *Forwardings;    ///< Array of pipeline forwarding pathes
  const InstrItinerary *Itineraries;    ///< Array of itineraries selected

  /// Ctors.
  ///
  InstrItineraryData() : SchedModel(MCSchedModel::GetDefaultSchedModel()),
                         Stages(nullptr), OperandCycles(nullptr),
                         Forwardings(nullptr), Itineraries(nullptr) {}

  InstrItineraryData(const MCSchedModel &SM, const InstrStage *S,
                     const unsigned *OS, const unsigned *F)
    : SchedModel(SM), Stages(S), OperandCycles(OS), Forwardings(F),
      Itineraries(SchedModel.InstrItineraries) {}

  /// isEmpty - Returns true if there are no itineraries.
  ///
  bool isEmpty() const { return Itineraries == nullptr; }

  /// isEndMarker - Returns true if the index is for the end marker
  /// itinerary.
  ///
  bool isEndMarker(unsigned ItinClassIndx) const {
    return ((Itineraries[ItinClassIndx].FirstStage == ~0U) &&
            (Itineraries[ItinClassIndx].LastStage == ~0U));
  }

  /// beginStage - Return the first stage of the itinerary.
  ///
  const InstrStage *beginStage(unsigned ItinClassIndx) const {
    unsigned StageIdx = Itineraries[ItinClassIndx].FirstStage;
    return Stages + StageIdx;
  }

  /// endStage - Return the last+1 stage of the itinerary.
  ///
  const InstrStage *endStage(unsigned ItinClassIndx) const {
    unsigned StageIdx = Itineraries[ItinClassIndx].LastStage;
    return Stages + StageIdx;
  }

  /// getStageLatency - Return the total stage latency of the given
  /// class.  The latency is the maximum completion time for any stage
  /// in the itinerary.
  ///
  /// If no stages exist, it defaults to one cycle.
  unsigned getStageLatency(unsigned ItinClassIndx) const {
    // If the target doesn't provide itinerary information, use a simple
    // non-zero default value for all instructions.
    if (isEmpty())
      return 1;

    // Calculate the maximum completion time for any stage.
    unsigned Latency = 0, StartCycle = 0;
    for (const InstrStage *IS = beginStage(ItinClassIndx),
           *E = endStage(ItinClassIndx); IS != E; ++IS) {
      Latency = std::max(Latency, StartCycle + IS->getCycles());
      StartCycle += IS->getNextCycles();
    }
    return Latency;
  }

  /// getOperandCycle - Return the cycle for the given class and
  /// operand. Return -1 if no cycle is specified for the operand.
  ///
  int getOperandCycle(unsigned ItinClassIndx, unsigned OperandIdx) const {
    if (isEmpty())
      return -1;

    unsigned FirstIdx = Itineraries[ItinClassIndx].FirstOperandCycle;
    unsigned LastIdx = Itineraries[ItinClassIndx].LastOperandCycle;
    if ((FirstIdx + OperandIdx) >= LastIdx)
      return -1;

    return (int)OperandCycles[FirstIdx + OperandIdx];
  }

  /// hasPipelineForwarding - Return true if there is a pipeline forwarding
  /// between instructions of itinerary classes DefClass and UseClasses so that
  /// value produced by an instruction of itinerary class DefClass, operand
  /// index DefIdx can be bypassed when it's read by an instruction of
  /// itinerary class UseClass, operand index UseIdx.
  bool hasPipelineForwarding(unsigned DefClass, unsigned DefIdx,
                             unsigned UseClass, unsigned UseIdx) const {
    unsigned FirstDefIdx = Itineraries[DefClass].FirstOperandCycle;
    unsigned LastDefIdx = Itineraries[DefClass].LastOperandCycle;
    if ((FirstDefIdx + DefIdx) >= LastDefIdx)
      return false;
    if (Forwardings[FirstDefIdx + DefIdx] == 0)
      return false;

    unsigned FirstUseIdx = Itineraries[UseClass].FirstOperandCycle;
    unsigned LastUseIdx = Itineraries[UseClass].LastOperandCycle;
    if ((FirstUseIdx + UseIdx) >= LastUseIdx)
      return false;

    return Forwardings[FirstDefIdx + DefIdx] ==
      Forwardings[FirstUseIdx + UseIdx];
  }

  /// getOperandLatency - Compute and return the use operand latency of a given
  /// itinerary class and operand index if the value is produced by an
  /// instruction of the specified itinerary class and def operand index.
  int getOperandLatency(unsigned DefClass, unsigned DefIdx,
                        unsigned UseClass, unsigned UseIdx) const {
    if (isEmpty())
      return -1;

    int DefCycle = getOperandCycle(DefClass, DefIdx);
    if (DefCycle == -1)
      return -1;

    int UseCycle = getOperandCycle(UseClass, UseIdx);
    if (UseCycle == -1)
      return -1;

    UseCycle = DefCycle - UseCycle + 1;
    if (UseCycle > 0 &&
        hasPipelineForwarding(DefClass, DefIdx, UseClass, UseIdx))
      // FIXME: This assumes one cycle benefit for every pipeline forwarding.
      --UseCycle;
    return UseCycle;
  }

  /// getNumMicroOps - Return the number of micro-ops that the given class
  /// decodes to. Return -1 for classes that require dynamic lookup via
  /// TargetInstrInfo.
  int getNumMicroOps(unsigned ItinClassIndx) const {
    if (isEmpty())
      return 1;
    return Itineraries[ItinClassIndx].NumMicroOps;
  }
};

} // End llvm namespace

#endif