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//===- llvm/MC/MCInstrItineraries.h - Scheduling ----------------*- 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
//
//===----------------------------------------------------------------------===//
//
// 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>
#include <optional>
namespace llvm {
//===----------------------------------------------------------------------===//
/// 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
/// consecutive 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
};
/// Bitmask representing a set of functional units.
typedef uint64_t FuncUnits;
unsigned Cycles_; ///< Length of stage in machine cycles
FuncUnits Units_; ///< Choice of functional units
int NextCycles_; ///< Number of machine cycles to next stage
ReservationKinds Kind_; ///< Kind of the FU reservation
/// Returns the number of cycles the stage is occupied.
unsigned getCycles() const {
return Cycles_;
}
/// Returns the choice of FUs.
FuncUnits getUnits() const {
return Units_;
}
ReservationKinds getReservationKind() const {
return Kind_;
}
/// 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_;
}
};
//===----------------------------------------------------------------------===//
/// An itinerary represents the scheduling information for an instruction.
/// This includes a set of stages occupied by the instruction and the pipeline
/// cycle in which operands are read and written.
///
struct InstrItinerary {
int16_t NumMicroOps; ///< # of micro-ops, -1 means it's variable
uint16_t FirstStage; ///< Index of first stage in itinerary
uint16_t LastStage; ///< Index of last + 1 stage in itinerary
uint16_t FirstOperandCycle; ///< Index of first operand rd/wr
uint16_t LastOperandCycle; ///< Index of last + 1 operand rd/wr
};
//===----------------------------------------------------------------------===//
/// Itinerary data supplied by a subtarget to be used by a target.
///
class InstrItineraryData {
public:
MCSchedModel SchedModel =
MCSchedModel::Default; ///< Basic machine properties.
const InstrStage *Stages = nullptr; ///< Array of stages selected
const unsigned *OperandCycles = nullptr; ///< Array of operand cycles selected
const unsigned *Forwardings = nullptr; ///< Array of pipeline forwarding paths
const InstrItinerary *Itineraries =
nullptr; ///< Array of itineraries selected
InstrItineraryData() = default;
InstrItineraryData(const MCSchedModel &SM, const InstrStage *S,
const unsigned *OS, const unsigned *F)
: SchedModel(SM), Stages(S), OperandCycles(OS), Forwardings(F),
Itineraries(SchedModel.InstrItineraries) {}
/// Returns true if there are no itineraries.
bool isEmpty() const { return Itineraries == nullptr; }
/// Returns true if the index is for the end marker itinerary.
bool isEndMarker(unsigned ItinClassIndx) const {
return ((Itineraries[ItinClassIndx].FirstStage == UINT16_MAX) &&
(Itineraries[ItinClassIndx].LastStage == UINT16_MAX));
}
/// Return the first stage of the itinerary.
const InstrStage *beginStage(unsigned ItinClassIndx) const {
unsigned StageIdx = Itineraries[ItinClassIndx].FirstStage;
return Stages + StageIdx;
}
/// Return the last+1 stage of the itinerary.
const InstrStage *endStage(unsigned ItinClassIndx) const {
unsigned StageIdx = Itineraries[ItinClassIndx].LastStage;
return Stages + StageIdx;
}
/// 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;
}
/// Return the cycle for the given class and operand. Return std::nullopt if
/// the information is not available for the operand.
std::optional<unsigned> getOperandCycle(unsigned ItinClassIndx,
unsigned OperandIdx) const {
if (isEmpty())
return std::nullopt;
unsigned FirstIdx = Itineraries[ItinClassIndx].FirstOperandCycle;
unsigned LastIdx = Itineraries[ItinClassIndx].LastOperandCycle;
if ((FirstIdx + OperandIdx) >= LastIdx)
return std::nullopt;
return OperandCycles[FirstIdx + OperandIdx];
}
/// 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];
}
/// 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. Return std::nullopt if
/// the information is not available for the operand.
std::optional<unsigned> getOperandLatency(unsigned DefClass, unsigned DefIdx,
unsigned UseClass,
unsigned UseIdx) const {
if (isEmpty())
return std::nullopt;
std::optional<unsigned> DefCycle = getOperandCycle(DefClass, DefIdx);
std::optional<unsigned> UseCycle = getOperandCycle(UseClass, UseIdx);
if (!DefCycle || !UseCycle)
return std::nullopt;
if (UseCycle > *DefCycle + 1)
return std::nullopt;
UseCycle = *DefCycle - *UseCycle + 1;
if (UseCycle > 0u &&
hasPipelineForwarding(DefClass, DefIdx, UseClass, UseIdx))
// FIXME: This assumes one cycle benefit for every pipeline forwarding.
UseCycle = *UseCycle - 1;
return UseCycle;
}
/// 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 namespace llvm
#endif // LLVM_MC_MCINSTRITINERARIES_H
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