1//===- ScheduleDAGInstrs.h - MachineInstr Scheduling ------------*- 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//
9/// \file Implements the ScheduleDAGInstrs class, which implements scheduling
10/// for a MachineInstr-based dependency graph.
11//
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_CODEGEN_SCHEDULEDAGINSTRS_H
15#define LLVM_CODEGEN_SCHEDULEDAGINSTRS_H
16
17#include "llvm/ADT/DenseMap.h"
18#include "llvm/ADT/PointerIntPair.h"
19#include "llvm/ADT/STLExtras.h"
20#include "llvm/ADT/SmallVector.h"
21#include "llvm/ADT/SparseMultiSet.h"
22#include "llvm/ADT/SparseSet.h"
23#include "llvm/CodeGen/LivePhysRegs.h"
24#include "llvm/CodeGen/MachineBasicBlock.h"
25#include "llvm/CodeGen/ScheduleDAG.h"
26#include "llvm/CodeGen/TargetRegisterInfo.h"
27#include "llvm/CodeGen/TargetSchedule.h"
28#include "llvm/MC/LaneBitmask.h"
29#include <cassert>
30#include <cstdint>
31#include <list>
32#include <utility>
33#include <vector>
34
35namespace llvm {
36
37  class AAResults;
38  class LiveIntervals;
39  class MachineFrameInfo;
40  class MachineFunction;
41  class MachineInstr;
42  class MachineLoopInfo;
43  class MachineOperand;
44  struct MCSchedClassDesc;
45  class PressureDiffs;
46  class PseudoSourceValue;
47  class RegPressureTracker;
48  class UndefValue;
49  class Value;
50
51  /// An individual mapping from virtual register number to SUnit.
52  struct VReg2SUnit {
53    unsigned VirtReg;
54    LaneBitmask LaneMask;
55    SUnit *SU;
56
57    VReg2SUnit(unsigned VReg, LaneBitmask LaneMask, SUnit *SU)
58      : VirtReg(VReg), LaneMask(LaneMask), SU(SU) {}
59
60    unsigned getSparseSetIndex() const {
61      return Register::virtReg2Index(VirtReg);
62    }
63  };
64
65  /// Mapping from virtual register to SUnit including an operand index.
66  struct VReg2SUnitOperIdx : public VReg2SUnit {
67    unsigned OperandIndex;
68
69    VReg2SUnitOperIdx(unsigned VReg, LaneBitmask LaneMask,
70                      unsigned OperandIndex, SUnit *SU)
71      : VReg2SUnit(VReg, LaneMask, SU), OperandIndex(OperandIndex) {}
72  };
73
74  /// Record a physical register access.
75  /// For non-data-dependent uses, OpIdx == -1.
76  struct PhysRegSUOper {
77    SUnit *SU;
78    int OpIdx;
79    unsigned Reg;
80
81    PhysRegSUOper(SUnit *su, int op, unsigned R): SU(su), OpIdx(op), Reg(R) {}
82
83    unsigned getSparseSetIndex() const { return Reg; }
84  };
85
86  /// Use a SparseMultiSet to track physical registers. Storage is only
87  /// allocated once for the pass. It can be cleared in constant time and reused
88  /// without any frees.
89  using Reg2SUnitsMap =
90      SparseMultiSet<PhysRegSUOper, identity<unsigned>, uint16_t>;
91
92  /// Use SparseSet as a SparseMap by relying on the fact that it never
93  /// compares ValueT's, only unsigned keys. This allows the set to be cleared
94  /// between scheduling regions in constant time as long as ValueT does not
95  /// require a destructor.
96  using VReg2SUnitMap = SparseSet<VReg2SUnit, VirtReg2IndexFunctor>;
97
98  /// Track local uses of virtual registers. These uses are gathered by the DAG
99  /// builder and may be consulted by the scheduler to avoid iterating an entire
100  /// vreg use list.
101  using VReg2SUnitMultiMap = SparseMultiSet<VReg2SUnit, VirtReg2IndexFunctor>;
102
103  using VReg2SUnitOperIdxMultiMap =
104      SparseMultiSet<VReg2SUnitOperIdx, VirtReg2IndexFunctor>;
105
106  using ValueType = PointerUnion<const Value *, const PseudoSourceValue *>;
107
108  struct UnderlyingObject : PointerIntPair<ValueType, 1, bool> {
109    UnderlyingObject(ValueType V, bool MayAlias)
110        : PointerIntPair<ValueType, 1, bool>(V, MayAlias) {}
111
112    ValueType getValue() const { return getPointer(); }
113    bool mayAlias() const { return getInt(); }
114  };
115
116  using UnderlyingObjectsVector = SmallVector<UnderlyingObject, 4>;
117
118  /// A ScheduleDAG for scheduling lists of MachineInstr.
119  class ScheduleDAGInstrs : public ScheduleDAG {
120  protected:
121    const MachineLoopInfo *MLI;
122    const MachineFrameInfo &MFI;
123
124    /// TargetSchedModel provides an interface to the machine model.
125    TargetSchedModel SchedModel;
126
127    /// True if the DAG builder should remove kill flags (in preparation for
128    /// rescheduling).
129    bool RemoveKillFlags;
130
131    /// The standard DAG builder does not normally include terminators as DAG
132    /// nodes because it does not create the necessary dependencies to prevent
133    /// reordering. A specialized scheduler can override
134    /// TargetInstrInfo::isSchedulingBoundary then enable this flag to indicate
135    /// it has taken responsibility for scheduling the terminator correctly.
136    bool CanHandleTerminators = false;
137
138    /// Whether lane masks should get tracked.
139    bool TrackLaneMasks = false;
140
141    // State specific to the current scheduling region.
142    // ------------------------------------------------
143
144    /// The block in which to insert instructions
145    MachineBasicBlock *BB;
146
147    /// The beginning of the range to be scheduled.
148    MachineBasicBlock::iterator RegionBegin;
149
150    /// The end of the range to be scheduled.
151    MachineBasicBlock::iterator RegionEnd;
152
153    /// Instructions in this region (distance(RegionBegin, RegionEnd)).
154    unsigned NumRegionInstrs;
155
156    /// After calling BuildSchedGraph, each machine instruction in the current
157    /// scheduling region is mapped to an SUnit.
158    DenseMap<MachineInstr*, SUnit*> MISUnitMap;
159
160    // State internal to DAG building.
161    // -------------------------------
162
163    /// Defs, Uses - Remember where defs and uses of each register are as we
164    /// iterate upward through the instructions. This is allocated here instead
165    /// of inside BuildSchedGraph to avoid the need for it to be initialized and
166    /// destructed for each block.
167    Reg2SUnitsMap Defs;
168    Reg2SUnitsMap Uses;
169
170    /// Tracks the last instruction(s) in this region defining each virtual
171    /// register. There may be multiple current definitions for a register with
172    /// disjunct lanemasks.
173    VReg2SUnitMultiMap CurrentVRegDefs;
174    /// Tracks the last instructions in this region using each virtual register.
175    VReg2SUnitOperIdxMultiMap CurrentVRegUses;
176
177    AAResults *AAForDep = nullptr;
178
179    /// Remember a generic side-effecting instruction as we proceed.
180    /// No other SU ever gets scheduled around it (except in the special
181    /// case of a huge region that gets reduced).
182    SUnit *BarrierChain = nullptr;
183
184  public:
185    /// A list of SUnits, used in Value2SUsMap, during DAG construction.
186    /// Note: to gain speed it might be worth investigating an optimized
187    /// implementation of this data structure, such as a singly linked list
188    /// with a memory pool (SmallVector was tried but slow and SparseSet is not
189    /// applicable).
190    using SUList = std::list<SUnit *>;
191
192  protected:
193    /// A map from ValueType to SUList, used during DAG construction, as
194    /// a means of remembering which SUs depend on which memory locations.
195    class Value2SUsMap;
196
197    /// Reduces maps in FIFO order, by N SUs. This is better than turning
198    /// every Nth memory SU into BarrierChain in buildSchedGraph(), since
199    /// it avoids unnecessary edges between seen SUs above the new BarrierChain,
200    /// and those below it.
201    void reduceHugeMemNodeMaps(Value2SUsMap &stores,
202                               Value2SUsMap &loads, unsigned N);
203
204    /// Adds a chain edge between SUa and SUb, but only if both
205    /// AAResults and Target fail to deny the dependency.
206    void addChainDependency(SUnit *SUa, SUnit *SUb,
207                            unsigned Latency = 0);
208
209    /// Adds dependencies as needed from all SUs in list to SU.
210    void addChainDependencies(SUnit *SU, SUList &SUs, unsigned Latency) {
211      for (SUnit *Entry : SUs)
212        addChainDependency(SU, Entry, Latency);
213    }
214
215    /// Adds dependencies as needed from all SUs in map, to SU.
216    void addChainDependencies(SUnit *SU, Value2SUsMap &Val2SUsMap);
217
218    /// Adds dependencies as needed to SU, from all SUs mapped to V.
219    void addChainDependencies(SUnit *SU, Value2SUsMap &Val2SUsMap,
220                              ValueType V);
221
222    /// Adds barrier chain edges from all SUs in map, and then clear the map.
223    /// This is equivalent to insertBarrierChain(), but optimized for the common
224    /// case where the new BarrierChain (a global memory object) has a higher
225    /// NodeNum than all SUs in map. It is assumed BarrierChain has been set
226    /// before calling this.
227    void addBarrierChain(Value2SUsMap &map);
228
229    /// Inserts a barrier chain in a huge region, far below current SU.
230    /// Adds barrier chain edges from all SUs in map with higher NodeNums than
231    /// this new BarrierChain, and remove them from map. It is assumed
232    /// BarrierChain has been set before calling this.
233    void insertBarrierChain(Value2SUsMap &map);
234
235    /// For an unanalyzable memory access, this Value is used in maps.
236    UndefValue *UnknownValue;
237
238
239    /// Topo - A topological ordering for SUnits which permits fast IsReachable
240    /// and similar queries.
241    ScheduleDAGTopologicalSort Topo;
242
243    using DbgValueVector =
244        std::vector<std::pair<MachineInstr *, MachineInstr *>>;
245    /// Remember instruction that precedes DBG_VALUE.
246    /// These are generated by buildSchedGraph but persist so they can be
247    /// referenced when emitting the final schedule.
248    DbgValueVector DbgValues;
249    MachineInstr *FirstDbgValue = nullptr;
250
251    /// Set of live physical registers for updating kill flags.
252    LivePhysRegs LiveRegs;
253
254  public:
255    explicit ScheduleDAGInstrs(MachineFunction &mf,
256                               const MachineLoopInfo *mli,
257                               bool RemoveKillFlags = false);
258
259    ~ScheduleDAGInstrs() override = default;
260
261    /// Gets the machine model for instruction scheduling.
262    const TargetSchedModel *getSchedModel() const { return &SchedModel; }
263
264    /// Resolves and cache a resolved scheduling class for an SUnit.
265    const MCSchedClassDesc *getSchedClass(SUnit *SU) const {
266      if (!SU->SchedClass && SchedModel.hasInstrSchedModel())
267        SU->SchedClass = SchedModel.resolveSchedClass(SU->getInstr());
268      return SU->SchedClass;
269    }
270
271    /// Returns an iterator to the top of the current scheduling region.
272    MachineBasicBlock::iterator begin() const { return RegionBegin; }
273
274    /// Returns an iterator to the bottom of the current scheduling region.
275    MachineBasicBlock::iterator end() const { return RegionEnd; }
276
277    /// Creates a new SUnit and return a ptr to it.
278    SUnit *newSUnit(MachineInstr *MI);
279
280    /// Returns an existing SUnit for this MI, or nullptr.
281    SUnit *getSUnit(MachineInstr *MI) const;
282
283    /// If this method returns true, handling of the scheduling regions
284    /// themselves (in case of a scheduling boundary in MBB) will be done
285    /// beginning with the topmost region of MBB.
286    virtual bool doMBBSchedRegionsTopDown() const { return false; }
287
288    /// Prepares to perform scheduling in the given block.
289    virtual void startBlock(MachineBasicBlock *BB);
290
291    /// Cleans up after scheduling in the given block.
292    virtual void finishBlock();
293
294    /// Initialize the DAG and common scheduler state for a new
295    /// scheduling region. This does not actually create the DAG, only clears
296    /// it. The scheduling driver may call BuildSchedGraph multiple times per
297    /// scheduling region.
298    virtual void enterRegion(MachineBasicBlock *bb,
299                             MachineBasicBlock::iterator begin,
300                             MachineBasicBlock::iterator end,
301                             unsigned regioninstrs);
302
303    /// Called when the scheduler has finished scheduling the current region.
304    virtual void exitRegion();
305
306    /// Builds SUnits for the current region.
307    /// If \p RPTracker is non-null, compute register pressure as a side effect.
308    /// The DAG builder is an efficient place to do it because it already visits
309    /// operands.
310    void buildSchedGraph(AAResults *AA,
311                         RegPressureTracker *RPTracker = nullptr,
312                         PressureDiffs *PDiffs = nullptr,
313                         LiveIntervals *LIS = nullptr,
314                         bool TrackLaneMasks = false);
315
316    /// Adds dependencies from instructions in the current list of
317    /// instructions being scheduled to scheduling barrier. We want to make sure
318    /// instructions which define registers that are either used by the
319    /// terminator or are live-out are properly scheduled. This is especially
320    /// important when the definition latency of the return value(s) are too
321    /// high to be hidden by the branch or when the liveout registers used by
322    /// instructions in the fallthrough block.
323    void addSchedBarrierDeps();
324
325    /// Orders nodes according to selected style.
326    ///
327    /// Typically, a scheduling algorithm will implement schedule() without
328    /// overriding enterRegion() or exitRegion().
329    virtual void schedule() = 0;
330
331    /// Allow targets to perform final scheduling actions at the level of the
332    /// whole MachineFunction. By default does nothing.
333    virtual void finalizeSchedule() {}
334
335    void dumpNode(const SUnit &SU) const override;
336    void dump() const override;
337
338    /// Returns a label for a DAG node that points to an instruction.
339    std::string getGraphNodeLabel(const SUnit *SU) const override;
340
341    /// Returns a label for the region of code covered by the DAG.
342    std::string getDAGName() const override;
343
344    /// Fixes register kill flags that scheduling has made invalid.
345    void fixupKills(MachineBasicBlock &MBB);
346
347    /// True if an edge can be added from PredSU to SuccSU without creating
348    /// a cycle.
349    bool canAddEdge(SUnit *SuccSU, SUnit *PredSU);
350
351    /// Add a DAG edge to the given SU with the given predecessor
352    /// dependence data.
353    ///
354    /// \returns true if the edge may be added without creating a cycle OR if an
355    /// equivalent edge already existed (false indicates failure).
356    bool addEdge(SUnit *SuccSU, const SDep &PredDep);
357
358  protected:
359    void initSUnits();
360    void addPhysRegDataDeps(SUnit *SU, unsigned OperIdx);
361    void addPhysRegDeps(SUnit *SU, unsigned OperIdx);
362    void addVRegDefDeps(SUnit *SU, unsigned OperIdx);
363    void addVRegUseDeps(SUnit *SU, unsigned OperIdx);
364
365    /// Initializes register live-range state for updating kills.
366    /// PostRA helper for rewriting kill flags.
367    void startBlockForKills(MachineBasicBlock *BB);
368
369    /// Toggles a register operand kill flag.
370    ///
371    /// Other adjustments may be made to the instruction if necessary. Return
372    /// true if the operand has been deleted, false if not.
373    void toggleKillFlag(MachineInstr &MI, MachineOperand &MO);
374
375    /// Returns a mask for which lanes get read/written by the given (register)
376    /// machine operand.
377    LaneBitmask getLaneMaskForMO(const MachineOperand &MO) const;
378
379    /// Returns true if the def register in \p MO has no uses.
380    bool deadDefHasNoUse(const MachineOperand &MO);
381  };
382
383  /// Creates a new SUnit and return a ptr to it.
384  inline SUnit *ScheduleDAGInstrs::newSUnit(MachineInstr *MI) {
385#ifndef NDEBUG
386    const SUnit *Addr = SUnits.empty() ? nullptr : &SUnits[0];
387#endif
388    SUnits.emplace_back(MI, (unsigned)SUnits.size());
389    assert((Addr == nullptr || Addr == &SUnits[0]) &&
390           "SUnits std::vector reallocated on the fly!");
391    return &SUnits.back();
392  }
393
394  /// Returns an existing SUnit for this MI, or nullptr.
395  inline SUnit *ScheduleDAGInstrs::getSUnit(MachineInstr *MI) const {
396    DenseMap<MachineInstr*, SUnit*>::const_iterator I = MISUnitMap.find(MI);
397    if (I == MISUnitMap.end())
398      return nullptr;
399    return I->second;
400  }
401
402} // end namespace llvm
403
404#endif // LLVM_CODEGEN_SCHEDULEDAGINSTRS_H
405