1//===- ScheduleDFS.h - ILP metric for ScheduleDAGInstrs ---------*- 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// Definition of an ILP metric for machine level instruction scheduling.
10//
11//===----------------------------------------------------------------------===//
12
13#ifndef LLVM_CODEGEN_SCHEDULEDFS_H
14#define LLVM_CODEGEN_SCHEDULEDFS_H
15
16#include "llvm/ADT/SmallVector.h"
17#include "llvm/CodeGen/ScheduleDAG.h"
18#include <cassert>
19#include <cstdint>
20#include <vector>
21
22namespace llvm {
23
24template <typename T> class ArrayRef;
25class raw_ostream;
26
27/// Represent the ILP of the subDAG rooted at a DAG node.
28///
29/// ILPValues summarize the DAG subtree rooted at each node. ILPValues are
30/// valid for all nodes regardless of their subtree membership.
31///
32/// When computed using bottom-up DFS, this metric assumes that the DAG is a
33/// forest of trees with roots at the bottom of the schedule branching upward.
34struct ILPValue {
35  unsigned InstrCount;
36  /// Length may either correspond to depth or height, depending on direction,
37  /// and cycles or nodes depending on context.
38  unsigned Length;
39
40  ILPValue(unsigned count, unsigned length):
41    InstrCount(count), Length(length) {}
42
43  // Order by the ILP metric's value.
44  bool operator<(ILPValue RHS) const {
45    return (uint64_t)InstrCount * RHS.Length
46      < (uint64_t)Length * RHS.InstrCount;
47  }
48  bool operator>(ILPValue RHS) const {
49    return RHS < *this;
50  }
51  bool operator<=(ILPValue RHS) const {
52    return (uint64_t)InstrCount * RHS.Length
53      <= (uint64_t)Length * RHS.InstrCount;
54  }
55  bool operator>=(ILPValue RHS) const {
56    return RHS <= *this;
57  }
58
59  void print(raw_ostream &OS) const;
60
61  void dump() const;
62};
63
64/// Compute the values of each DAG node for various metrics during DFS.
65class SchedDFSResult {
66  friend class SchedDFSImpl;
67
68  static const unsigned InvalidSubtreeID = ~0u;
69
70  /// Per-SUnit data computed during DFS for various metrics.
71  ///
72  /// A node's SubtreeID is set to itself when it is visited to indicate that it
73  /// is the root of a subtree. Later it is set to its parent to indicate an
74  /// interior node. Finally, it is set to a representative subtree ID during
75  /// finalization.
76  struct NodeData {
77    unsigned InstrCount = 0;
78    unsigned SubtreeID = InvalidSubtreeID;
79
80    NodeData() = default;
81  };
82
83  /// Per-Subtree data computed during DFS.
84  struct TreeData {
85    unsigned ParentTreeID = InvalidSubtreeID;
86    unsigned SubInstrCount = 0;
87
88    TreeData() = default;
89  };
90
91  /// Record a connection between subtrees and the connection level.
92  struct Connection {
93    unsigned TreeID;
94    unsigned Level;
95
96    Connection(unsigned tree, unsigned level): TreeID(tree), Level(level) {}
97  };
98
99  bool IsBottomUp;
100  unsigned SubtreeLimit;
101  /// DFS results for each SUnit in this DAG.
102  std::vector<NodeData> DFSNodeData;
103
104  // Store per-tree data indexed on tree ID,
105  SmallVector<TreeData, 16> DFSTreeData;
106
107  // For each subtree discovered during DFS, record its connections to other
108  // subtrees.
109  std::vector<SmallVector<Connection, 4>> SubtreeConnections;
110
111  /// Cache the current connection level of each subtree.
112  /// This mutable array is updated during scheduling.
113  std::vector<unsigned> SubtreeConnectLevels;
114
115public:
116  SchedDFSResult(bool IsBU, unsigned lim)
117    : IsBottomUp(IsBU), SubtreeLimit(lim) {}
118
119  /// Get the node cutoff before subtrees are considered significant.
120  unsigned getSubtreeLimit() const { return SubtreeLimit; }
121
122  /// Return true if this DFSResult is uninitialized.
123  ///
124  /// resize() initializes DFSResult, while compute() populates it.
125  bool empty() const { return DFSNodeData.empty(); }
126
127  /// Clear the results.
128  void clear() {
129    DFSNodeData.clear();
130    DFSTreeData.clear();
131    SubtreeConnections.clear();
132    SubtreeConnectLevels.clear();
133  }
134
135  /// Initialize the result data with the size of the DAG.
136  void resize(unsigned NumSUnits) {
137    DFSNodeData.resize(NumSUnits);
138  }
139
140  /// Compute various metrics for the DAG with given roots.
141  void compute(ArrayRef<SUnit> SUnits);
142
143  /// Get the number of instructions in the given subtree and its
144  /// children.
145  unsigned getNumInstrs(const SUnit *SU) const {
146    return DFSNodeData[SU->NodeNum].InstrCount;
147  }
148
149  /// Get the number of instructions in the given subtree not including
150  /// children.
151  unsigned getNumSubInstrs(unsigned SubtreeID) const {
152    return DFSTreeData[SubtreeID].SubInstrCount;
153  }
154
155  /// Get the ILP value for a DAG node.
156  ///
157  /// A leaf node has an ILP of 1/1.
158  ILPValue getILP(const SUnit *SU) const {
159    return ILPValue(DFSNodeData[SU->NodeNum].InstrCount, 1 + SU->getDepth());
160  }
161
162  /// The number of subtrees detected in this DAG.
163  unsigned getNumSubtrees() const { return SubtreeConnectLevels.size(); }
164
165  /// Get the ID of the subtree the given DAG node belongs to.
166  ///
167  /// For convenience, if DFSResults have not been computed yet, give everything
168  /// tree ID 0.
169  unsigned getSubtreeID(const SUnit *SU) const {
170    if (empty())
171      return 0;
172    assert(SU->NodeNum < DFSNodeData.size() &&  "New Node");
173    return DFSNodeData[SU->NodeNum].SubtreeID;
174  }
175
176  /// Get the connection level of a subtree.
177  ///
178  /// For bottom-up trees, the connection level is the latency depth (in cycles)
179  /// of the deepest connection to another subtree.
180  unsigned getSubtreeLevel(unsigned SubtreeID) const {
181    return SubtreeConnectLevels[SubtreeID];
182  }
183
184  /// Scheduler callback to update SubtreeConnectLevels when a tree is
185  /// initially scheduled.
186  void scheduleTree(unsigned SubtreeID);
187};
188
189raw_ostream &operator<<(raw_ostream &OS, const ILPValue &Val);
190
191} // end namespace llvm
192
193#endif // LLVM_CODEGEN_SCHEDULEDFS_H
194