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 
28 namespace llvm {
29 
30 template <>
31 inline void DominatorTreeBase<MachineBasicBlock, false>::addRoot(
32     MachineBasicBlock *MBB) {
33   this->Roots.push_back(MBB);
34 }
35 
36 extern template class DomTreeNodeBase<MachineBasicBlock>;
37 extern template class DominatorTreeBase<MachineBasicBlock, false>; // DomTree
38 extern template class DominatorTreeBase<MachineBasicBlock, true>; // PostDomTree
39 
40 using MachineDomTreeNode = DomTreeNodeBase<MachineBasicBlock>;
41 
42 //===-------------------------------------
43 /// DominatorTree Class - Concrete subclass of DominatorTreeBase that is used to
44 /// compute a normal dominator tree.
45 ///
46 class 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 
80 public:
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 
258 template <class Node, class ChildIterator>
259 struct 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 
268 template <class T> struct GraphTraits;
269 
270 template <>
271 struct GraphTraits<MachineDomTreeNode *>
272     : public MachineDomTreeGraphTraitsBase<MachineDomTreeNode,
273                                            MachineDomTreeNode::iterator> {};
274 
275 template <>
276 struct GraphTraits<const MachineDomTreeNode *>
277     : public MachineDomTreeGraphTraitsBase<const MachineDomTreeNode,
278                                            MachineDomTreeNode::const_iterator> {
279 };
280 
281 template <> 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