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  /// getRoots -  Return the root blocks of the current CFG.  This may include
97  /// multiple blocks if we are computing post dominators.  For forward
98  /// dominators, this will always be a single block (the entry node).
99  ///
100  const SmallVectorImpl<MachineBasicBlock*> &getRoots() const {
101    applySplitCriticalEdges();
102    return DT->getRoots();
103  }
104
105  MachineBasicBlock *getRoot() const {
106    applySplitCriticalEdges();
107    return DT->getRoot();
108  }
109
110  MachineDomTreeNode *getRootNode() const {
111    applySplitCriticalEdges();
112    return DT->getRootNode();
113  }
114
115  bool runOnMachineFunction(MachineFunction &F) override;
116
117  void calculate(MachineFunction &F);
118
119  bool dominates(const MachineDomTreeNode *A,
120                 const MachineDomTreeNode *B) const {
121    applySplitCriticalEdges();
122    return DT->dominates(A, B);
123  }
124
125  bool dominates(const MachineBasicBlock *A, const MachineBasicBlock *B) const {
126    applySplitCriticalEdges();
127    return DT->dominates(A, B);
128  }
129
130  // dominates - Return true if A dominates B. This performs the
131  // special checks necessary if A and B are in the same basic block.
132  bool dominates(const MachineInstr *A, const MachineInstr *B) const {
133    applySplitCriticalEdges();
134    const MachineBasicBlock *BBA = A->getParent(), *BBB = B->getParent();
135    if (BBA != BBB) return DT->dominates(BBA, BBB);
136
137    // Loop through the basic block until we find A or B.
138    MachineBasicBlock::const_iterator I = BBA->begin();
139    for (; &*I != A && &*I != B; ++I)
140      /*empty*/ ;
141
142    return &*I == A;
143  }
144
145  bool properlyDominates(const MachineDomTreeNode *A,
146                         const MachineDomTreeNode *B) const {
147    applySplitCriticalEdges();
148    return DT->properlyDominates(A, B);
149  }
150
151  bool properlyDominates(const MachineBasicBlock *A,
152                         const MachineBasicBlock *B) const {
153    applySplitCriticalEdges();
154    return DT->properlyDominates(A, B);
155  }
156
157  /// findNearestCommonDominator - Find nearest common dominator basic block
158  /// for basic block A and B. If there is no such block then return NULL.
159  MachineBasicBlock *findNearestCommonDominator(MachineBasicBlock *A,
160                                                MachineBasicBlock *B) {
161    applySplitCriticalEdges();
162    return DT->findNearestCommonDominator(A, B);
163  }
164
165  MachineDomTreeNode *operator[](MachineBasicBlock *BB) const {
166    applySplitCriticalEdges();
167    return DT->getNode(BB);
168  }
169
170  /// getNode - return the (Post)DominatorTree node for the specified basic
171  /// block.  This is the same as using operator[] on this class.
172  ///
173  MachineDomTreeNode *getNode(MachineBasicBlock *BB) const {
174    applySplitCriticalEdges();
175    return DT->getNode(BB);
176  }
177
178  /// addNewBlock - Add a new node to the dominator tree information.  This
179  /// creates a new node as a child of DomBB dominator node,linking it into
180  /// the children list of the immediate dominator.
181  MachineDomTreeNode *addNewBlock(MachineBasicBlock *BB,
182                                  MachineBasicBlock *DomBB) {
183    applySplitCriticalEdges();
184    return DT->addNewBlock(BB, DomBB);
185  }
186
187  /// changeImmediateDominator - This method is used to update the dominator
188  /// tree information when a node's immediate dominator changes.
189  ///
190  void changeImmediateDominator(MachineBasicBlock *N,
191                                MachineBasicBlock *NewIDom) {
192    applySplitCriticalEdges();
193    DT->changeImmediateDominator(N, NewIDom);
194  }
195
196  void changeImmediateDominator(MachineDomTreeNode *N,
197                                MachineDomTreeNode *NewIDom) {
198    applySplitCriticalEdges();
199    DT->changeImmediateDominator(N, NewIDom);
200  }
201
202  /// eraseNode - Removes a node from  the dominator tree. Block must not
203  /// dominate any other blocks. Removes node from its immediate dominator's
204  /// children list. Deletes dominator node associated with basic block BB.
205  void eraseNode(MachineBasicBlock *BB) {
206    applySplitCriticalEdges();
207    DT->eraseNode(BB);
208  }
209
210  /// splitBlock - BB is split and now it has one successor. Update dominator
211  /// tree to reflect this change.
212  void splitBlock(MachineBasicBlock* NewBB) {
213    applySplitCriticalEdges();
214    DT->splitBlock(NewBB);
215  }
216
217  /// isReachableFromEntry - Return true if A is dominated by the entry
218  /// block of the function containing it.
219  bool isReachableFromEntry(const MachineBasicBlock *A) {
220    applySplitCriticalEdges();
221    return DT->isReachableFromEntry(A);
222  }
223
224  void releaseMemory() override;
225
226  void verifyAnalysis() const override;
227
228  void print(raw_ostream &OS, const Module*) const override;
229
230  /// Record that the critical edge (FromBB, ToBB) has been
231  /// split with NewBB.
232  /// This is best to use this method instead of directly update the
233  /// underlying information, because this helps mitigating the
234  /// number of time the DT information is invalidated.
235  ///
236  /// \note Do not use this method with regular edges.
237  ///
238  /// \note To benefit from the compile time improvement incurred by this
239  /// method, the users of this method have to limit the queries to the DT
240  /// interface between two edges splitting. In other words, they have to
241  /// pack the splitting of critical edges as much as possible.
242  void recordSplitCriticalEdge(MachineBasicBlock *FromBB,
243                              MachineBasicBlock *ToBB,
244                              MachineBasicBlock *NewBB) {
245    bool Inserted = NewBBs.insert(NewBB).second;
246    (void)Inserted;
247    assert(Inserted &&
248           "A basic block inserted via edge splitting cannot appear twice");
249    CriticalEdgesToSplit.push_back({FromBB, ToBB, NewBB});
250  }
251};
252
253//===-------------------------------------
254/// DominatorTree GraphTraits specialization so the DominatorTree can be
255/// iterable by generic graph iterators.
256///
257
258template <class Node, class ChildIterator>
259struct MachineDomTreeGraphTraitsBase {
260  using NodeRef = Node *;
261  using ChildIteratorType = ChildIterator;
262
263  static NodeRef getEntryNode(NodeRef N) { return N; }
264  static ChildIteratorType child_begin(NodeRef N) { return N->begin(); }
265  static ChildIteratorType child_end(NodeRef N) { return N->end(); }
266};
267
268template <class T> struct GraphTraits;
269
270template <>
271struct GraphTraits<MachineDomTreeNode *>
272    : public MachineDomTreeGraphTraitsBase<MachineDomTreeNode,
273                                           MachineDomTreeNode::iterator> {};
274
275template <>
276struct GraphTraits<const MachineDomTreeNode *>
277    : public MachineDomTreeGraphTraitsBase<const MachineDomTreeNode,
278                                           MachineDomTreeNode::const_iterator> {
279};
280
281template <> struct GraphTraits<MachineDominatorTree*>
282  : public GraphTraits<MachineDomTreeNode *> {
283  static NodeRef getEntryNode(MachineDominatorTree *DT) {
284    return DT->getRootNode();
285  }
286};
287
288} // end namespace llvm
289
290#endif // LLVM_CODEGEN_MACHINEDOMINATORS_H
291