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/CodeGen/MachineInstrBundleIterator.h"
23 #include "llvm/Support/GenericDomTree.h"
24 #include "llvm/Support/GenericDomTreeConstruction.h"
25 #include <cassert>
26 #include <memory>
27 
28 namespace llvm {
29 class AnalysisUsage;
30 class MachineFunction;
31 class Module;
32 class raw_ostream;
33 
34 template <>
35 inline void DominatorTreeBase<MachineBasicBlock, false>::addRoot(
36     MachineBasicBlock *MBB) {
37   this->Roots.push_back(MBB);
38 }
39 
40 extern template class DomTreeNodeBase<MachineBasicBlock>;
41 extern template class DominatorTreeBase<MachineBasicBlock, false>; // DomTree
42 extern template class DominatorTreeBase<MachineBasicBlock, true>; // PostDomTree
43 
44 using MachineDomTree = DomTreeBase<MachineBasicBlock>;
45 using MachineDomTreeNode = DomTreeNodeBase<MachineBasicBlock>;
46 
47 //===-------------------------------------
48 /// DominatorTree Class - Concrete subclass of DominatorTreeBase that is used to
49 /// compute a normal dominator tree.
50 ///
51 class MachineDominatorTree : public MachineFunctionPass {
52   /// Helper structure used to hold all the basic blocks
53   /// involved in the split of a critical edge.
54   struct CriticalEdge {
55     MachineBasicBlock *FromBB;
56     MachineBasicBlock *ToBB;
57     MachineBasicBlock *NewBB;
58   };
59 
60   /// Pile up all the critical edges to be split.
61   /// The splitting of a critical edge is local and thus, it is possible
62   /// to apply several of those changes at the same time.
63   mutable SmallVector<CriticalEdge, 32> CriticalEdgesToSplit;
64 
65   /// Remember all the basic blocks that are inserted during
66   /// edge splitting.
67   /// Invariant: NewBBs == all the basic blocks contained in the NewBB
68   /// field of all the elements of CriticalEdgesToSplit.
69   /// I.e., forall elt in CriticalEdgesToSplit, it exists BB in NewBBs
70   /// such as BB == elt.NewBB.
71   mutable SmallSet<MachineBasicBlock *, 32> NewBBs;
72 
73   /// The DominatorTreeBase that is used to compute a normal dominator tree.
74   std::unique_ptr<MachineDomTree> DT;
75 
76   /// Apply all the recorded critical edges to the DT.
77   /// This updates the underlying DT information in a way that uses
78   /// the fast query path of DT as much as possible.
79   ///
80   /// \post CriticalEdgesToSplit.empty().
81   void applySplitCriticalEdges() const;
82 
83 public:
84   static char ID; // Pass ID, replacement for typeid
85 
86   MachineDominatorTree();
87   explicit MachineDominatorTree(MachineFunction &MF) : MachineFunctionPass(ID) {
88     calculate(MF);
89   }
90 
91   MachineDomTree &getBase() {
92     if (!DT)
93       DT.reset(new MachineDomTree());
94     applySplitCriticalEdges();
95     return *DT;
96   }
97 
98   void getAnalysisUsage(AnalysisUsage &AU) const override;
99 
100   MachineBasicBlock *getRoot() const {
101     applySplitCriticalEdges();
102     return DT->getRoot();
103   }
104 
105   MachineDomTreeNode *getRootNode() const {
106     applySplitCriticalEdges();
107     return DT->getRootNode();
108   }
109 
110   bool runOnMachineFunction(MachineFunction &F) override;
111 
112   void calculate(MachineFunction &F);
113 
114   bool dominates(const MachineDomTreeNode *A,
115                  const MachineDomTreeNode *B) const {
116     applySplitCriticalEdges();
117     return DT->dominates(A, B);
118   }
119 
120   void getDescendants(MachineBasicBlock *A,
121                       SmallVectorImpl<MachineBasicBlock *> &Result) {
122     applySplitCriticalEdges();
123     DT->getDescendants(A, Result);
124   }
125 
126   bool dominates(const MachineBasicBlock *A, const MachineBasicBlock *B) const {
127     applySplitCriticalEdges();
128     return DT->dominates(A, B);
129   }
130 
131   // dominates - Return true if A dominates B. This performs the
132   // special checks necessary if A and B are in the same basic block.
133   bool dominates(const MachineInstr *A, const MachineInstr *B) const {
134     applySplitCriticalEdges();
135     const MachineBasicBlock *BBA = A->getParent(), *BBB = B->getParent();
136     if (BBA != BBB) return DT->dominates(BBA, BBB);
137 
138     // Loop through the basic block until we find A or B.
139     MachineBasicBlock::const_iterator I = BBA->begin();
140     for (; &*I != A && &*I != B; ++I)
141       /*empty*/ ;
142 
143     return &*I == A;
144   }
145 
146   bool properlyDominates(const MachineDomTreeNode *A,
147                          const MachineDomTreeNode *B) const {
148     applySplitCriticalEdges();
149     return DT->properlyDominates(A, B);
150   }
151 
152   bool properlyDominates(const MachineBasicBlock *A,
153                          const MachineBasicBlock *B) const {
154     applySplitCriticalEdges();
155     return DT->properlyDominates(A, B);
156   }
157 
158   /// findNearestCommonDominator - Find nearest common dominator basic block
159   /// for basic block A and B. If there is no such block then return NULL.
160   MachineBasicBlock *findNearestCommonDominator(MachineBasicBlock *A,
161                                                 MachineBasicBlock *B) {
162     applySplitCriticalEdges();
163     return DT->findNearestCommonDominator(A, B);
164   }
165 
166   MachineDomTreeNode *operator[](MachineBasicBlock *BB) const {
167     applySplitCriticalEdges();
168     return DT->getNode(BB);
169   }
170 
171   /// getNode - return the (Post)DominatorTree node for the specified basic
172   /// block.  This is the same as using operator[] on this class.
173   ///
174   MachineDomTreeNode *getNode(MachineBasicBlock *BB) const {
175     applySplitCriticalEdges();
176     return DT->getNode(BB);
177   }
178 
179   /// addNewBlock - Add a new node to the dominator tree information.  This
180   /// creates a new node as a child of DomBB dominator node,linking it into
181   /// the children list of the immediate dominator.
182   MachineDomTreeNode *addNewBlock(MachineBasicBlock *BB,
183                                   MachineBasicBlock *DomBB) {
184     applySplitCriticalEdges();
185     return DT->addNewBlock(BB, DomBB);
186   }
187 
188   /// changeImmediateDominator - This method is used to update the dominator
189   /// tree information when a node's immediate dominator changes.
190   ///
191   void changeImmediateDominator(MachineBasicBlock *N,
192                                 MachineBasicBlock *NewIDom) {
193     applySplitCriticalEdges();
194     DT->changeImmediateDominator(N, NewIDom);
195   }
196 
197   void changeImmediateDominator(MachineDomTreeNode *N,
198                                 MachineDomTreeNode *NewIDom) {
199     applySplitCriticalEdges();
200     DT->changeImmediateDominator(N, NewIDom);
201   }
202 
203   /// eraseNode - Removes a node from  the dominator tree. Block must not
204   /// dominate any other blocks. Removes node from its immediate dominator's
205   /// children list. Deletes dominator node associated with basic block BB.
206   void eraseNode(MachineBasicBlock *BB) {
207     applySplitCriticalEdges();
208     DT->eraseNode(BB);
209   }
210 
211   /// splitBlock - BB is split and now it has one successor. Update dominator
212   /// tree to reflect this change.
213   void splitBlock(MachineBasicBlock* NewBB) {
214     applySplitCriticalEdges();
215     DT->splitBlock(NewBB);
216   }
217 
218   /// isReachableFromEntry - Return true if A is dominated by the entry
219   /// block of the function containing it.
220   bool isReachableFromEntry(const MachineBasicBlock *A) {
221     applySplitCriticalEdges();
222     return DT->isReachableFromEntry(A);
223   }
224 
225   void releaseMemory() override;
226 
227   void verifyAnalysis() const override;
228 
229   void print(raw_ostream &OS, const Module*) const override;
230 
231   /// Record that the critical edge (FromBB, ToBB) has been
232   /// split with NewBB.
233   /// This is best to use this method instead of directly update the
234   /// underlying information, because this helps mitigating the
235   /// number of time the DT information is invalidated.
236   ///
237   /// \note Do not use this method with regular edges.
238   ///
239   /// \note To benefit from the compile time improvement incurred by this
240   /// method, the users of this method have to limit the queries to the DT
241   /// interface between two edges splitting. In other words, they have to
242   /// pack the splitting of critical edges as much as possible.
243   void recordSplitCriticalEdge(MachineBasicBlock *FromBB,
244                               MachineBasicBlock *ToBB,
245                               MachineBasicBlock *NewBB) {
246     bool Inserted = NewBBs.insert(NewBB).second;
247     (void)Inserted;
248     assert(Inserted &&
249            "A basic block inserted via edge splitting cannot appear twice");
250     CriticalEdgesToSplit.push_back({FromBB, ToBB, NewBB});
251   }
252 };
253 
254 //===-------------------------------------
255 /// DominatorTree GraphTraits specialization so the DominatorTree can be
256 /// iterable by generic graph iterators.
257 ///
258 
259 template <class Node, class ChildIterator>
260 struct MachineDomTreeGraphTraitsBase {
261   using NodeRef = Node *;
262   using ChildIteratorType = ChildIterator;
263 
264   static NodeRef getEntryNode(NodeRef N) { return N; }
265   static ChildIteratorType child_begin(NodeRef N) { return N->begin(); }
266   static ChildIteratorType child_end(NodeRef N) { return N->end(); }
267 };
268 
269 template <class T> struct GraphTraits;
270 
271 template <>
272 struct GraphTraits<MachineDomTreeNode *>
273     : public MachineDomTreeGraphTraitsBase<MachineDomTreeNode,
274                                            MachineDomTreeNode::const_iterator> {
275 };
276 
277 template <>
278 struct GraphTraits<const MachineDomTreeNode *>
279     : public MachineDomTreeGraphTraitsBase<const MachineDomTreeNode,
280                                            MachineDomTreeNode::const_iterator> {
281 };
282 
283 template <> struct GraphTraits<MachineDominatorTree*>
284   : public GraphTraits<MachineDomTreeNode *> {
285   static NodeRef getEntryNode(MachineDominatorTree *DT) {
286     return DT->getRootNode();
287   }
288 };
289 
290 } // end namespace llvm
291 
292 #endif // LLVM_CODEGEN_MACHINEDOMINATORS_H
293