1//==- llvm/CodeGen/MachineDominators.h - Machine Dom Calculation -*- 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// This file defines classes mirroring those in llvm/Analysis/Dominators.h,
10// but for target-specific code rather than target-independent IR.
11//
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_CODEGEN_MACHINEDOMINATORS_H
15#define LLVM_CODEGEN_MACHINEDOMINATORS_H
16
17#include "llvm/ADT/SmallSet.h"
18#include "llvm/ADT/SmallVector.h"
19#include "llvm/CodeGen/MachineBasicBlock.h"
20#include "llvm/CodeGen/MachineFunctionPass.h"
21#include "llvm/CodeGen/MachineInstr.h"
22#include "llvm/Support/GenericDomTree.h"
23#include "llvm/Support/GenericDomTreeConstruction.h"
24#include <cassert>
25#include <memory>
26#include <vector>
27
28namespace llvm {
29
30template <>
31inline void DominatorTreeBase<MachineBasicBlock, false>::addRoot(
32    MachineBasicBlock *MBB) {
33  this->Roots.push_back(MBB);
34}
35
36extern template class DomTreeNodeBase<MachineBasicBlock>;
37extern template class DominatorTreeBase<MachineBasicBlock, false>; // DomTree
38extern template class DominatorTreeBase<MachineBasicBlock, true>; // PostDomTree
39
40using MachineDomTreeNode = DomTreeNodeBase<MachineBasicBlock>;
41
42//===-------------------------------------
43/// DominatorTree Class - Concrete subclass of DominatorTreeBase that is used to
44/// compute a normal dominator tree.
45///
46class MachineDominatorTree : public MachineFunctionPass {
47  using DomTreeT = DomTreeBase<MachineBasicBlock>;
48
49  /// Helper structure used to hold all the basic blocks
50  /// involved in the split of a critical edge.
51  struct CriticalEdge {
52    MachineBasicBlock *FromBB;
53    MachineBasicBlock *ToBB;
54    MachineBasicBlock *NewBB;
55  };
56
57  /// Pile up all the critical edges to be split.
58  /// The splitting of a critical edge is local and thus, it is possible
59  /// to apply several of those changes at the same time.
60  mutable SmallVector<CriticalEdge, 32> CriticalEdgesToSplit;
61
62  /// Remember all the basic blocks that are inserted during
63  /// edge splitting.
64  /// Invariant: NewBBs == all the basic blocks contained in the NewBB
65  /// field of all the elements of CriticalEdgesToSplit.
66  /// I.e., forall elt in CriticalEdgesToSplit, it exists BB in NewBBs
67  /// such as BB == elt.NewBB.
68  mutable SmallSet<MachineBasicBlock *, 32> NewBBs;
69
70  /// The DominatorTreeBase that is used to compute a normal dominator tree.
71  std::unique_ptr<DomTreeT> DT;
72
73  /// Apply all the recorded critical edges to the DT.
74  /// This updates the underlying DT information in a way that uses
75  /// the fast query path of DT as much as possible.
76  ///
77  /// \post CriticalEdgesToSplit.empty().
78  void applySplitCriticalEdges() const;
79
80public:
81  static char ID; // Pass ID, replacement for typeid
82
83  MachineDominatorTree();
84  explicit MachineDominatorTree(MachineFunction &MF) : MachineFunctionPass(ID) {
85    calculate(MF);
86  }
87
88  DomTreeT &getBase() {
89    if (!DT) DT.reset(new DomTreeT());
90    applySplitCriticalEdges();
91    return *DT;
92  }
93
94  void getAnalysisUsage(AnalysisUsage &AU) const override;
95
96  MachineBasicBlock *getRoot() const {
97    applySplitCriticalEdges();
98    return DT->getRoot();
99  }
100
101  MachineDomTreeNode *getRootNode() const {
102    applySplitCriticalEdges();
103    return DT->getRootNode();
104  }
105
106  bool runOnMachineFunction(MachineFunction &F) override;
107
108  void calculate(MachineFunction &F);
109
110  bool dominates(const MachineDomTreeNode *A,
111                 const MachineDomTreeNode *B) const {
112    applySplitCriticalEdges();
113    return DT->dominates(A, B);
114  }
115
116  bool dominates(const MachineBasicBlock *A, const MachineBasicBlock *B) const {
117    applySplitCriticalEdges();
118    return DT->dominates(A, B);
119  }
120
121  // dominates - Return true if A dominates B. This performs the
122  // special checks necessary if A and B are in the same basic block.
123  bool dominates(const MachineInstr *A, const MachineInstr *B) const {
124    applySplitCriticalEdges();
125    const MachineBasicBlock *BBA = A->getParent(), *BBB = B->getParent();
126    if (BBA != BBB) return DT->dominates(BBA, BBB);
127
128    // Loop through the basic block until we find A or B.
129    MachineBasicBlock::const_iterator I = BBA->begin();
130    for (; &*I != A && &*I != B; ++I)
131      /*empty*/ ;
132
133    return &*I == A;
134  }
135
136  bool properlyDominates(const MachineDomTreeNode *A,
137                         const MachineDomTreeNode *B) const {
138    applySplitCriticalEdges();
139    return DT->properlyDominates(A, B);
140  }
141
142  bool properlyDominates(const MachineBasicBlock *A,
143                         const MachineBasicBlock *B) const {
144    applySplitCriticalEdges();
145    return DT->properlyDominates(A, B);
146  }
147
148  /// findNearestCommonDominator - Find nearest common dominator basic block
149  /// for basic block A and B. If there is no such block then return NULL.
150  MachineBasicBlock *findNearestCommonDominator(MachineBasicBlock *A,
151                                                MachineBasicBlock *B) {
152    applySplitCriticalEdges();
153    return DT->findNearestCommonDominator(A, B);
154  }
155
156  MachineDomTreeNode *operator[](MachineBasicBlock *BB) const {
157    applySplitCriticalEdges();
158    return DT->getNode(BB);
159  }
160
161  /// getNode - return the (Post)DominatorTree node for the specified basic
162  /// block.  This is the same as using operator[] on this class.
163  ///
164  MachineDomTreeNode *getNode(MachineBasicBlock *BB) const {
165    applySplitCriticalEdges();
166    return DT->getNode(BB);
167  }
168
169  /// addNewBlock - Add a new node to the dominator tree information.  This
170  /// creates a new node as a child of DomBB dominator node,linking it into
171  /// the children list of the immediate dominator.
172  MachineDomTreeNode *addNewBlock(MachineBasicBlock *BB,
173                                  MachineBasicBlock *DomBB) {
174    applySplitCriticalEdges();
175    return DT->addNewBlock(BB, DomBB);
176  }
177
178  /// changeImmediateDominator - This method is used to update the dominator
179  /// tree information when a node's immediate dominator changes.
180  ///
181  void changeImmediateDominator(MachineBasicBlock *N,
182                                MachineBasicBlock *NewIDom) {
183    applySplitCriticalEdges();
184    DT->changeImmediateDominator(N, NewIDom);
185  }
186
187  void changeImmediateDominator(MachineDomTreeNode *N,
188                                MachineDomTreeNode *NewIDom) {
189    applySplitCriticalEdges();
190    DT->changeImmediateDominator(N, NewIDom);
191  }
192
193  /// eraseNode - Removes a node from  the dominator tree. Block must not
194  /// dominate any other blocks. Removes node from its immediate dominator's
195  /// children list. Deletes dominator node associated with basic block BB.
196  void eraseNode(MachineBasicBlock *BB) {
197    applySplitCriticalEdges();
198    DT->eraseNode(BB);
199  }
200
201  /// splitBlock - BB is split and now it has one successor. Update dominator
202  /// tree to reflect this change.
203  void splitBlock(MachineBasicBlock* NewBB) {
204    applySplitCriticalEdges();
205    DT->splitBlock(NewBB);
206  }
207
208  /// isReachableFromEntry - Return true if A is dominated by the entry
209  /// block of the function containing it.
210  bool isReachableFromEntry(const MachineBasicBlock *A) {
211    applySplitCriticalEdges();
212    return DT->isReachableFromEntry(A);
213  }
214
215  void releaseMemory() override;
216
217  void verifyAnalysis() const override;
218
219  void print(raw_ostream &OS, const Module*) const override;
220
221  /// Record that the critical edge (FromBB, ToBB) has been
222  /// split with NewBB.
223  /// This is best to use this method instead of directly update the
224  /// underlying information, because this helps mitigating the
225  /// number of time the DT information is invalidated.
226  ///
227  /// \note Do not use this method with regular edges.
228  ///
229  /// \note To benefit from the compile time improvement incurred by this
230  /// method, the users of this method have to limit the queries to the DT
231  /// interface between two edges splitting. In other words, they have to
232  /// pack the splitting of critical edges as much as possible.
233  void recordSplitCriticalEdge(MachineBasicBlock *FromBB,
234                              MachineBasicBlock *ToBB,
235                              MachineBasicBlock *NewBB) {
236    bool Inserted = NewBBs.insert(NewBB).second;
237    (void)Inserted;
238    assert(Inserted &&
239           "A basic block inserted via edge splitting cannot appear twice");
240    CriticalEdgesToSplit.push_back({FromBB, ToBB, NewBB});
241  }
242};
243
244//===-------------------------------------
245/// DominatorTree GraphTraits specialization so the DominatorTree can be
246/// iterable by generic graph iterators.
247///
248
249template <class Node, class ChildIterator>
250struct MachineDomTreeGraphTraitsBase {
251  using NodeRef = Node *;
252  using ChildIteratorType = ChildIterator;
253
254  static NodeRef getEntryNode(NodeRef N) { return N; }
255  static ChildIteratorType child_begin(NodeRef N) { return N->begin(); }
256  static ChildIteratorType child_end(NodeRef N) { return N->end(); }
257};
258
259template <class T> struct GraphTraits;
260
261template <>
262struct GraphTraits<MachineDomTreeNode *>
263    : public MachineDomTreeGraphTraitsBase<MachineDomTreeNode,
264                                           MachineDomTreeNode::const_iterator> {
265};
266
267template <>
268struct GraphTraits<const MachineDomTreeNode *>
269    : public MachineDomTreeGraphTraitsBase<const MachineDomTreeNode,
270                                           MachineDomTreeNode::const_iterator> {
271};
272
273template <> struct GraphTraits<MachineDominatorTree*>
274  : public GraphTraits<MachineDomTreeNode *> {
275  static NodeRef getEntryNode(MachineDominatorTree *DT) {
276    return DT->getRootNode();
277  }
278};
279
280} // end namespace llvm
281
282#endif // LLVM_CODEGEN_MACHINEDOMINATORS_H
283