annotate lib/Analysis/CFG.cpp @ 120:1172e4bd9c6f

update 4.0.0
author mir3636
date Fri, 25 Nov 2016 19:14:25 +0900
parents 7d135dc70f03
children c2174574ed3a
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1 //===-- CFG.cpp - BasicBlock analysis --------------------------------------==//
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2 //
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3 // The LLVM Compiler Infrastructure
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4 //
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5 // This file is distributed under the University of Illinois Open Source
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6 // License. See LICENSE.TXT for details.
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7 //
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8 //===----------------------------------------------------------------------===//
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9 //
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10 // This family of functions performs analyses on basic blocks, and instructions
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11 // contained within basic blocks.
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12 //
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13 //===----------------------------------------------------------------------===//
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14
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15 #include "llvm/Analysis/CFG.h"
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16 #include "llvm/ADT/SmallSet.h"
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17 #include "llvm/Analysis/LoopInfo.h"
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18 #include "llvm/IR/Dominators.h"
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19
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20 using namespace llvm;
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21
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22 /// FindFunctionBackedges - Analyze the specified function to find all of the
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23 /// loop backedges in the function and return them. This is a relatively cheap
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24 /// (compared to computing dominators and loop info) analysis.
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25 ///
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26 /// The output is added to Result, as pairs of <from,to> edge info.
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27 void llvm::FindFunctionBackedges(const Function &F,
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28 SmallVectorImpl<std::pair<const BasicBlock*,const BasicBlock*> > &Result) {
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29 const BasicBlock *BB = &F.getEntryBlock();
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30 if (succ_empty(BB))
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31 return;
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32
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33 SmallPtrSet<const BasicBlock*, 8> Visited;
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34 SmallVector<std::pair<const BasicBlock*, succ_const_iterator>, 8> VisitStack;
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35 SmallPtrSet<const BasicBlock*, 8> InStack;
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36
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37 Visited.insert(BB);
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38 VisitStack.push_back(std::make_pair(BB, succ_begin(BB)));
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39 InStack.insert(BB);
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40 do {
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41 std::pair<const BasicBlock*, succ_const_iterator> &Top = VisitStack.back();
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42 const BasicBlock *ParentBB = Top.first;
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43 succ_const_iterator &I = Top.second;
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44
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45 bool FoundNew = false;
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46 while (I != succ_end(ParentBB)) {
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47 BB = *I++;
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48 if (Visited.insert(BB).second) {
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49 FoundNew = true;
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50 break;
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51 }
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52 // Successor is in VisitStack, it's a back edge.
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53 if (InStack.count(BB))
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54 Result.push_back(std::make_pair(ParentBB, BB));
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55 }
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56
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57 if (FoundNew) {
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58 // Go down one level if there is a unvisited successor.
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59 InStack.insert(BB);
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60 VisitStack.push_back(std::make_pair(BB, succ_begin(BB)));
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61 } else {
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62 // Go up one level.
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63 InStack.erase(VisitStack.pop_back_val().first);
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64 }
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65 } while (!VisitStack.empty());
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66 }
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67
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68 /// GetSuccessorNumber - Search for the specified successor of basic block BB
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69 /// and return its position in the terminator instruction's list of
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70 /// successors. It is an error to call this with a block that is not a
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71 /// successor.
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72 unsigned llvm::GetSuccessorNumber(const BasicBlock *BB,
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73 const BasicBlock *Succ) {
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74 const TerminatorInst *Term = BB->getTerminator();
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75 #ifndef NDEBUG
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76 unsigned e = Term->getNumSuccessors();
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77 #endif
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78 for (unsigned i = 0; ; ++i) {
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79 assert(i != e && "Didn't find edge?");
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80 if (Term->getSuccessor(i) == Succ)
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81 return i;
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82 }
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83 }
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84
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85 /// isCriticalEdge - Return true if the specified edge is a critical edge.
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86 /// Critical edges are edges from a block with multiple successors to a block
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87 /// with multiple predecessors.
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88 bool llvm::isCriticalEdge(const TerminatorInst *TI, unsigned SuccNum,
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89 bool AllowIdenticalEdges) {
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90 assert(SuccNum < TI->getNumSuccessors() && "Illegal edge specification!");
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91 if (TI->getNumSuccessors() == 1) return false;
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92
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93 const BasicBlock *Dest = TI->getSuccessor(SuccNum);
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94 const_pred_iterator I = pred_begin(Dest), E = pred_end(Dest);
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95
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96 // If there is more than one predecessor, this is a critical edge...
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97 assert(I != E && "No preds, but we have an edge to the block?");
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98 const BasicBlock *FirstPred = *I;
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99 ++I; // Skip one edge due to the incoming arc from TI.
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100 if (!AllowIdenticalEdges)
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101 return I != E;
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102
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103 // If AllowIdenticalEdges is true, then we allow this edge to be considered
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104 // non-critical iff all preds come from TI's block.
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105 for (; I != E; ++I)
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106 if (*I != FirstPred)
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107 return true;
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108 return false;
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109 }
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110
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111 // LoopInfo contains a mapping from basic block to the innermost loop. Find
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112 // the outermost loop in the loop nest that contains BB.
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113 static const Loop *getOutermostLoop(const LoopInfo *LI, const BasicBlock *BB) {
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114 const Loop *L = LI->getLoopFor(BB);
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115 if (L) {
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116 while (const Loop *Parent = L->getParentLoop())
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117 L = Parent;
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118 }
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119 return L;
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120 }
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121
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122 // True if there is a loop which contains both BB1 and BB2.
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123 static bool loopContainsBoth(const LoopInfo *LI,
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124 const BasicBlock *BB1, const BasicBlock *BB2) {
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125 const Loop *L1 = getOutermostLoop(LI, BB1);
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126 const Loop *L2 = getOutermostLoop(LI, BB2);
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127 return L1 != nullptr && L1 == L2;
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128 }
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129
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130 bool llvm::isPotentiallyReachableFromMany(
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents: 83
diff changeset
131 SmallVectorImpl<BasicBlock *> &Worklist, BasicBlock *StopBB,
afa8332a0e37 LLVM 3.8
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents: 83
diff changeset
132 const DominatorTree *DT, const LoopInfo *LI) {
0
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
133 // When the stop block is unreachable, it's dominated from everywhere,
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
134 // regardless of whether there's a path between the two blocks.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
135 if (DT && !DT->isReachableFromEntry(StopBB))
77
54457678186b LLVM 3.6
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents: 0
diff changeset
136 DT = nullptr;
0
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
137
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
138 // Limit the number of blocks we visit. The goal is to avoid run-away compile
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
139 // times on large CFGs without hampering sensible code. Arbitrarily chosen.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
140 unsigned Limit = 32;
120
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
141 SmallPtrSet<const BasicBlock*, 32> Visited;
0
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
142 do {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
143 BasicBlock *BB = Worklist.pop_back_val();
83
60c9769439b8 LLVM 3.7
Tatsuki IHA <e125716@ie.u-ryukyu.ac.jp>
parents: 77
diff changeset
144 if (!Visited.insert(BB).second)
0
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
145 continue;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
146 if (BB == StopBB)
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
147 return true;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
148 if (DT && DT->dominates(BB, StopBB))
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
149 return true;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
150 if (LI && loopContainsBoth(LI, BB, StopBB))
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
151 return true;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
152
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
153 if (!--Limit) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
154 // We haven't been able to prove it one way or the other. Conservatively
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
155 // answer true -- that there is potentially a path.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
156 return true;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
157 }
95c75e76d11b LLVM 3.4
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parents:
diff changeset
158
77
54457678186b LLVM 3.6
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parents: 0
diff changeset
159 if (const Loop *Outer = LI ? getOutermostLoop(LI, BB) : nullptr) {
0
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
160 // All blocks in a single loop are reachable from all other blocks. From
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
161 // any of these blocks, we can skip directly to the exits of the loop,
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
162 // ignoring any other blocks inside the loop body.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
163 Outer->getExitBlocks(Worklist);
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
164 } else {
77
54457678186b LLVM 3.6
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parents: 0
diff changeset
165 Worklist.append(succ_begin(BB), succ_end(BB));
0
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
166 }
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
167 } while (!Worklist.empty());
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
168
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
169 // We have exhausted all possible paths and are certain that 'To' can not be
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
170 // reached from 'From'.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
171 return false;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
172 }
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
173
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
174 bool llvm::isPotentiallyReachable(const BasicBlock *A, const BasicBlock *B,
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
175 const DominatorTree *DT, const LoopInfo *LI) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
176 assert(A->getParent() == B->getParent() &&
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
177 "This analysis is function-local!");
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
178
95c75e76d11b LLVM 3.4
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parents:
diff changeset
179 SmallVector<BasicBlock*, 32> Worklist;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
180 Worklist.push_back(const_cast<BasicBlock*>(A));
95c75e76d11b LLVM 3.4
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parents:
diff changeset
181
95
afa8332a0e37 LLVM 3.8
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents: 83
diff changeset
182 return isPotentiallyReachableFromMany(Worklist, const_cast<BasicBlock *>(B),
afa8332a0e37 LLVM 3.8
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents: 83
diff changeset
183 DT, LI);
0
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
184 }
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
185
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
186 bool llvm::isPotentiallyReachable(const Instruction *A, const Instruction *B,
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
187 const DominatorTree *DT, const LoopInfo *LI) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
188 assert(A->getParent()->getParent() == B->getParent()->getParent() &&
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
189 "This analysis is function-local!");
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
190
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
191 SmallVector<BasicBlock*, 32> Worklist;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
192
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
193 if (A->getParent() == B->getParent()) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
194 // The same block case is special because it's the only time we're looking
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
195 // within a single block to see which instruction comes first. Once we
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
196 // start looking at multiple blocks, the first instruction of the block is
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
197 // reachable, so we only need to determine reachability between whole
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
198 // blocks.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
199 BasicBlock *BB = const_cast<BasicBlock *>(A->getParent());
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
200
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
201 // If the block is in a loop then we can reach any instruction in the block
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
202 // from any other instruction in the block by going around a backedge.
77
54457678186b LLVM 3.6
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents: 0
diff changeset
203 if (LI && LI->getLoopFor(BB) != nullptr)
0
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
204 return true;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
205
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
206 // Linear scan, start at 'A', see whether we hit 'B' or the end first.
95
afa8332a0e37 LLVM 3.8
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents: 83
diff changeset
207 for (BasicBlock::const_iterator I = A->getIterator(), E = BB->end(); I != E;
afa8332a0e37 LLVM 3.8
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents: 83
diff changeset
208 ++I) {
0
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
209 if (&*I == B)
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
210 return true;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
211 }
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
212
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
213 // Can't be in a loop if it's the entry block -- the entry block may not
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
214 // have predecessors.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
215 if (BB == &BB->getParent()->getEntryBlock())
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
216 return false;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
217
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
218 // Otherwise, continue doing the normal per-BB CFG walk.
77
54457678186b LLVM 3.6
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents: 0
diff changeset
219 Worklist.append(succ_begin(BB), succ_end(BB));
0
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
220
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
221 if (Worklist.empty()) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
222 // We've proven that there's no path!
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
223 return false;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
224 }
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
225 } else {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
226 Worklist.push_back(const_cast<BasicBlock*>(A->getParent()));
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
227 }
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
228
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
229 if (A->getParent() == &A->getParent()->getParent()->getEntryBlock())
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
230 return true;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
231 if (B->getParent() == &A->getParent()->getParent()->getEntryBlock())
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
232 return false;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
233
95
afa8332a0e37 LLVM 3.8
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents: 83
diff changeset
234 return isPotentiallyReachableFromMany(
afa8332a0e37 LLVM 3.8
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents: 83
diff changeset
235 Worklist, const_cast<BasicBlock *>(B->getParent()), DT, LI);
0
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
236 }