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//===- llvm/CodeGen/DFAPacketizer.h - DFA Packetizer for VLIW ---*- 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 class implements a deterministic finite automaton (DFA) based
// packetizing mechanism for VLIW architectures. It provides APIs to
// determine whether there exists a legal mapping of instructions to
// functional unit assignments in a packet. The DFA is auto-generated from
// the target's Schedule.td file.
//
// A DFA consists of 3 major elements: states, inputs, and transitions. For
// the packetizing mechanism, the input is the set of instruction classes for
// a target. The state models all possible combinations of functional unit
// consumption for a given set of instructions in a packet. A transition
// models the addition of an instruction to a packet. In the DFA constructed
// by this class, if an instruction can be added to a packet, then a valid
// transition exists from the corresponding state. Invalid transitions
// indicate that the instruction cannot be added to the current packet.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_CODEGEN_DFAPACKETIZER_H
#define LLVM_CODEGEN_DFAPACKETIZER_H
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/ScheduleDAGInstrs.h"
#include "llvm/CodeGen/ScheduleDAGMutation.h"
#include "llvm/Support/Automaton.h"
#include <cstdint>
#include <map>
#include <memory>
#include <utility>
#include <vector>
namespace llvm {
class ScheduleDAGMutation;
class InstrItineraryData;
class MachineFunction;
class MachineInstr;
class MachineLoopInfo;
class MCInstrDesc;
class SUnit;
class TargetInstrInfo;
// This class extends ScheduleDAGInstrs and overrides the schedule method
// to build the dependence graph.
class DefaultVLIWScheduler : public ScheduleDAGInstrs {
private:
AAResults *AA;
/// Ordered list of DAG postprocessing steps.
std::vector<std::unique_ptr<ScheduleDAGMutation>> Mutations;
public:
DefaultVLIWScheduler(MachineFunction &MF, MachineLoopInfo &MLI,
AAResults *AA);
// Actual scheduling work.
void schedule() override;
/// DefaultVLIWScheduler takes ownership of the Mutation object.
void addMutation(std::unique_ptr<ScheduleDAGMutation> Mutation) {
Mutations.push_back(std::move(Mutation));
}
protected:
void postProcessDAG();
};
class DFAPacketizer {
private:
const InstrItineraryData *InstrItins;
Automaton<uint64_t> A;
/// For every itinerary, an "action" to apply to the automaton. This removes
/// the redundancy in actions between itinerary classes.
ArrayRef<unsigned> ItinActions;
public:
DFAPacketizer(const InstrItineraryData *InstrItins, Automaton<uint64_t> a,
ArrayRef<unsigned> ItinActions)
: InstrItins(InstrItins), A(std::move(a)), ItinActions(ItinActions) {
// Start off with resource tracking disabled.
A.enableTranscription(false);
}
// Reset the current state to make all resources available.
void clearResources() {
A.reset();
}
// Set whether this packetizer should track not just whether instructions
// can be packetized, but also which functional units each instruction ends up
// using after packetization.
void setTrackResources(bool Track) {
A.enableTranscription(Track);
}
// Check if the resources occupied by a MCInstrDesc are available in
// the current state.
bool canReserveResources(const MCInstrDesc *MID);
// Reserve the resources occupied by a MCInstrDesc and change the current
// state to reflect that change.
void reserveResources(const MCInstrDesc *MID);
// Check if the resources occupied by a machine instruction are available
// in the current state.
bool canReserveResources(MachineInstr &MI);
// Reserve the resources occupied by a machine instruction and change the
// current state to reflect that change.
void reserveResources(MachineInstr &MI);
// Return the resources used by the InstIdx'th instruction added to this
// packet. The resources are returned as a bitvector of functional units.
//
// Note that a bundle may be packed in multiple valid ways. This function
// returns one arbitary valid packing.
//
// Requires setTrackResources(true) to have been called.
unsigned getUsedResources(unsigned InstIdx);
const InstrItineraryData *getInstrItins() const { return InstrItins; }
};
// VLIWPacketizerList implements a simple VLIW packetizer using DFA. The
// packetizer works on machine basic blocks. For each instruction I in BB,
// the packetizer consults the DFA to see if machine resources are available
// to execute I. If so, the packetizer checks if I depends on any instruction
// in the current packet. If no dependency is found, I is added to current
// packet and the machine resource is marked as taken. If any dependency is
// found, a target API call is made to prune the dependence.
class VLIWPacketizerList {
protected:
MachineFunction &MF;
const TargetInstrInfo *TII;
AAResults *AA;
// The VLIW Scheduler.
DefaultVLIWScheduler *VLIWScheduler;
// Vector of instructions assigned to the current packet.
std::vector<MachineInstr*> CurrentPacketMIs;
// DFA resource tracker.
DFAPacketizer *ResourceTracker;
// Map: MI -> SU.
std::map<MachineInstr*, SUnit*> MIToSUnit;
public:
// The AAResults parameter can be nullptr.
VLIWPacketizerList(MachineFunction &MF, MachineLoopInfo &MLI,
AAResults *AA);
VLIWPacketizerList &operator=(const VLIWPacketizerList &other) = delete;
VLIWPacketizerList(const VLIWPacketizerList &other) = delete;
virtual ~VLIWPacketizerList();
// Implement this API in the backend to bundle instructions.
void PacketizeMIs(MachineBasicBlock *MBB,
MachineBasicBlock::iterator BeginItr,
MachineBasicBlock::iterator EndItr);
// Return the ResourceTracker.
DFAPacketizer *getResourceTracker() {return ResourceTracker;}
// addToPacket - Add MI to the current packet.
virtual MachineBasicBlock::iterator addToPacket(MachineInstr &MI) {
CurrentPacketMIs.push_back(&MI);
ResourceTracker->reserveResources(MI);
return MI;
}
// End the current packet and reset the state of the packetizer.
// Overriding this function allows the target-specific packetizer
// to perform custom finalization.
virtual void endPacket(MachineBasicBlock *MBB,
MachineBasicBlock::iterator MI);
// Perform initialization before packetizing an instruction. This
// function is supposed to be overrided by the target dependent packetizer.
virtual void initPacketizerState() {}
// Check if the given instruction I should be ignored by the packetizer.
virtual bool ignorePseudoInstruction(const MachineInstr &I,
const MachineBasicBlock *MBB) {
return false;
}
// Return true if instruction MI can not be packetized with any other
// instruction, which means that MI itself is a packet.
virtual bool isSoloInstruction(const MachineInstr &MI) { return true; }
// Check if the packetizer should try to add the given instruction to
// the current packet. One reasons for which it may not be desirable
// to include an instruction in the current packet could be that it
// would cause a stall.
// If this function returns "false", the current packet will be ended,
// and the instruction will be added to the next packet.
virtual bool shouldAddToPacket(const MachineInstr &MI) { return true; }
// Check if it is legal to packetize SUI and SUJ together.
virtual bool isLegalToPacketizeTogether(SUnit *SUI, SUnit *SUJ) {
return false;
}
// Check if it is legal to prune dependece between SUI and SUJ.
virtual bool isLegalToPruneDependencies(SUnit *SUI, SUnit *SUJ) {
return false;
}
// Add a DAG mutation to be done before the packetization begins.
void addMutation(std::unique_ptr<ScheduleDAGMutation> Mutation);
bool alias(const MachineInstr &MI1, const MachineInstr &MI2,
bool UseTBAA = true) const;
private:
bool alias(const MachineMemOperand &Op1, const MachineMemOperand &Op2,
bool UseTBAA = true) const;
};
} // end namespace llvm
#endif // LLVM_CODEGEN_DFAPACKETIZER_H
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