1//===- llvm/CodeGen/DFAPacketizer.h - DFA Packetizer for VLIW ---*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8// This class implements a deterministic finite automaton (DFA) based
9// packetizing mechanism for VLIW architectures. It provides APIs to
10// determine whether there exists a legal mapping of instructions to
11// functional unit assignments in a packet. The DFA is auto-generated from
12// the target's Schedule.td file.
13//
14// A DFA consists of 3 major elements: states, inputs, and transitions. For
15// the packetizing mechanism, the input is the set of instruction classes for
16// a target. The state models all possible combinations of functional unit
17// consumption for a given set of instructions in a packet. A transition
18// models the addition of an instruction to a packet. In the DFA constructed
19// by this class, if an instruction can be added to a packet, then a valid
20// transition exists from the corresponding state. Invalid transitions
21// indicate that the instruction cannot be added to the current packet.
22//
23//===----------------------------------------------------------------------===//
24
25#ifndef LLVM_CODEGEN_DFAPACKETIZER_H
26#define LLVM_CODEGEN_DFAPACKETIZER_H
27
28#include "llvm/ADT/DenseMap.h"
29#include "llvm/CodeGen/MachineBasicBlock.h"
30#include "llvm/CodeGen/ScheduleDAGMutation.h"
31#include "llvm/Support/Automaton.h"
32#include <cstdint>
33#include <map>
34#include <memory>
35#include <utility>
36#include <vector>
37
38namespace llvm {
39
40class DefaultVLIWScheduler;
41class InstrItineraryData;
42class MachineFunction;
43class MachineInstr;
44class MachineLoopInfo;
45class MCInstrDesc;
46class SUnit;
47class TargetInstrInfo;
48
49class DFAPacketizer {
50private:
51  const InstrItineraryData *InstrItins;
52  Automaton<uint64_t> A;
53  /// For every itinerary, an "action" to apply to the automaton. This removes
54  /// the redundancy in actions between itinerary classes.
55  ArrayRef<unsigned> ItinActions;
56
57public:
58  DFAPacketizer(const InstrItineraryData *InstrItins, Automaton<uint64_t> a,
59                ArrayRef<unsigned> ItinActions)
60      : InstrItins(InstrItins), A(std::move(a)), ItinActions(ItinActions) {
61    // Start off with resource tracking disabled.
62    A.enableTranscription(false);
63  }
64
65  // Reset the current state to make all resources available.
66  void clearResources() {
67    A.reset();
68  }
69
70  // Set whether this packetizer should track not just whether instructions
71  // can be packetized, but also which functional units each instruction ends up
72  // using after packetization.
73  void setTrackResources(bool Track) {
74    A.enableTranscription(Track);
75  }
76
77  // Check if the resources occupied by a MCInstrDesc are available in
78  // the current state.
79  bool canReserveResources(const MCInstrDesc *MID);
80
81  // Reserve the resources occupied by a MCInstrDesc and change the current
82  // state to reflect that change.
83  void reserveResources(const MCInstrDesc *MID);
84
85  // Check if the resources occupied by a machine instruction are available
86  // in the current state.
87  bool canReserveResources(MachineInstr &MI);
88
89  // Reserve the resources occupied by a machine instruction and change the
90  // current state to reflect that change.
91  void reserveResources(MachineInstr &MI);
92
93  // Return the resources used by the InstIdx'th instruction added to this
94  // packet. The resources are returned as a bitvector of functional units.
95  //
96  // Note that a bundle may be packed in multiple valid ways. This function
97  // returns one arbitary valid packing.
98  //
99  // Requires setTrackResources(true) to have been called.
100  unsigned getUsedResources(unsigned InstIdx);
101
102  const InstrItineraryData *getInstrItins() const { return InstrItins; }
103};
104
105// VLIWPacketizerList implements a simple VLIW packetizer using DFA. The
106// packetizer works on machine basic blocks. For each instruction I in BB,
107// the packetizer consults the DFA to see if machine resources are available
108// to execute I. If so, the packetizer checks if I depends on any instruction
109// in the current packet. If no dependency is found, I is added to current
110// packet and the machine resource is marked as taken. If any dependency is
111// found, a target API call is made to prune the dependence.
112class VLIWPacketizerList {
113protected:
114  MachineFunction &MF;
115  const TargetInstrInfo *TII;
116  AAResults *AA;
117
118  // The VLIW Scheduler.
119  DefaultVLIWScheduler *VLIWScheduler;
120  // Vector of instructions assigned to the current packet.
121  std::vector<MachineInstr*> CurrentPacketMIs;
122  // DFA resource tracker.
123  DFAPacketizer *ResourceTracker;
124  // Map: MI -> SU.
125  std::map<MachineInstr*, SUnit*> MIToSUnit;
126
127public:
128  // The AAResults parameter can be nullptr.
129  VLIWPacketizerList(MachineFunction &MF, MachineLoopInfo &MLI,
130                     AAResults *AA);
131
132  virtual ~VLIWPacketizerList();
133
134  // Implement this API in the backend to bundle instructions.
135  void PacketizeMIs(MachineBasicBlock *MBB,
136                    MachineBasicBlock::iterator BeginItr,
137                    MachineBasicBlock::iterator EndItr);
138
139  // Return the ResourceTracker.
140  DFAPacketizer *getResourceTracker() {return ResourceTracker;}
141
142  // addToPacket - Add MI to the current packet.
143  virtual MachineBasicBlock::iterator addToPacket(MachineInstr &MI) {
144    CurrentPacketMIs.push_back(&MI);
145    ResourceTracker->reserveResources(MI);
146    return MI;
147  }
148
149  // End the current packet and reset the state of the packetizer.
150  // Overriding this function allows the target-specific packetizer
151  // to perform custom finalization.
152  virtual void endPacket(MachineBasicBlock *MBB,
153                         MachineBasicBlock::iterator MI);
154
155  // Perform initialization before packetizing an instruction. This
156  // function is supposed to be overrided by the target dependent packetizer.
157  virtual void initPacketizerState() {}
158
159  // Check if the given instruction I should be ignored by the packetizer.
160  virtual bool ignorePseudoInstruction(const MachineInstr &I,
161                                       const MachineBasicBlock *MBB) {
162    return false;
163  }
164
165  // Return true if instruction MI can not be packetized with any other
166  // instruction, which means that MI itself is a packet.
167  virtual bool isSoloInstruction(const MachineInstr &MI) { return true; }
168
169  // Check if the packetizer should try to add the given instruction to
170  // the current packet. One reasons for which it may not be desirable
171  // to include an instruction in the current packet could be that it
172  // would cause a stall.
173  // If this function returns "false", the current packet will be ended,
174  // and the instruction will be added to the next packet.
175  virtual bool shouldAddToPacket(const MachineInstr &MI) { return true; }
176
177  // Check if it is legal to packetize SUI and SUJ together.
178  virtual bool isLegalToPacketizeTogether(SUnit *SUI, SUnit *SUJ) {
179    return false;
180  }
181
182  // Check if it is legal to prune dependece between SUI and SUJ.
183  virtual bool isLegalToPruneDependencies(SUnit *SUI, SUnit *SUJ) {
184    return false;
185  }
186
187  // Add a DAG mutation to be done before the packetization begins.
188  void addMutation(std::unique_ptr<ScheduleDAGMutation> Mutation);
189
190  bool alias(const MachineInstr &MI1, const MachineInstr &MI2,
191             bool UseTBAA = true) const;
192
193private:
194  bool alias(const MachineMemOperand &Op1, const MachineMemOperand &Op2,
195             bool UseTBAA = true) const;
196};
197
198} // end namespace llvm
199
200#endif // LLVM_CODEGEN_DFAPACKETIZER_H
201