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annotate lib/CodeGen/UnreachableBlockElim.cpp @ 120:1172e4bd9c6f

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update 4.0.0
author mir3636
date Fri, 25 Nov 2016 19:14:25 +0900
parents afa8332a0e37
children 803732b1fca8
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1 //===-- UnreachableBlockElim.cpp - Remove unreachable blocks for codegen --===//
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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 pass is an extremely simple version of the SimplifyCFG pass. Its sole
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11 // job is to delete LLVM basic blocks that are not reachable from the entry
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12 // node. To do this, it performs a simple depth first traversal of the CFG,
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13 // then deletes any unvisited nodes.
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14 //
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15 // Note that this pass is really a hack. In particular, the instruction
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16 // selectors for various targets should just not generate code for unreachable
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17 // blocks. Until LLVM has a more systematic way of defining instruction
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18 // selectors, however, we cannot really expect them to handle additional
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19 // complexity.
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20 //
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21 //===----------------------------------------------------------------------===//
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22
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23 #include "llvm/CodeGen/UnreachableBlockElim.h"
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24 #include "llvm/ADT/DepthFirstIterator.h"
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25 #include "llvm/ADT/SmallPtrSet.h"
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26 #include "llvm/CodeGen/MachineDominators.h"
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27 #include "llvm/CodeGen/MachineFunctionPass.h"
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28 #include "llvm/CodeGen/MachineLoopInfo.h"
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29 #include "llvm/CodeGen/MachineModuleInfo.h"
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30 #include "llvm/CodeGen/MachineRegisterInfo.h"
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31 #include "llvm/CodeGen/Passes.h"
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32 #include "llvm/IR/CFG.h"
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33 #include "llvm/IR/Constant.h"
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34 #include "llvm/IR/Dominators.h"
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35 #include "llvm/IR/Function.h"
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36 #include "llvm/IR/Instructions.h"
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37 #include "llvm/IR/Type.h"
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38 #include "llvm/Pass.h"
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39 #include "llvm/Target/TargetInstrInfo.h"
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40 using namespace llvm;
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41
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42 static bool eliminateUnreachableBlock(Function &F) {
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43 df_iterator_default_set<BasicBlock*> Reachable;
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44
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45 // Mark all reachable blocks.
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46 for (BasicBlock *BB : depth_first_ext(&F, Reachable))
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47 (void)BB/* Mark all reachable blocks */;
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48
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49 // Loop over all dead blocks, remembering them and deleting all instructions
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50 // in them.
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51 std::vector<BasicBlock*> DeadBlocks;
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52 for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
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53 if (!Reachable.count(&*I)) {
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54 BasicBlock *BB = &*I;
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55 DeadBlocks.push_back(BB);
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56 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
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57 PN->replaceAllUsesWith(Constant::getNullValue(PN->getType()));
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58 BB->getInstList().pop_front();
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59 }
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60 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
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61 (*SI)->removePredecessor(BB);
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62 BB->dropAllReferences();
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63 }
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64
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65 // Actually remove the blocks now.
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66 for (unsigned i = 0, e = DeadBlocks.size(); i != e; ++i) {
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67 DeadBlocks[i]->eraseFromParent();
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68 }
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69
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70 return !DeadBlocks.empty();
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71 }
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72
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73 namespace {
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74 class UnreachableBlockElimLegacyPass : public FunctionPass {
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75 bool runOnFunction(Function &F) override {
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76 return eliminateUnreachableBlock(F);
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77 }
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78
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79 public:
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80 static char ID; // Pass identification, replacement for typeid
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81 UnreachableBlockElimLegacyPass() : FunctionPass(ID) {
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82 initializeUnreachableBlockElimLegacyPassPass(
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83 *PassRegistry::getPassRegistry());
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84 }
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85
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86 void getAnalysisUsage(AnalysisUsage &AU) const override {
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87 AU.addPreserved<DominatorTreeWrapperPass>();
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88 }
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89 };
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90 }
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91 char UnreachableBlockElimLegacyPass::ID = 0;
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92 INITIALIZE_PASS(UnreachableBlockElimLegacyPass, "unreachableblockelim",
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93 "Remove unreachable blocks from the CFG", false, false)
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94
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95 FunctionPass *llvm::createUnreachableBlockEliminationPass() {
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96 return new UnreachableBlockElimLegacyPass();
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97 }
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98
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99 PreservedAnalyses UnreachableBlockElimPass::run(Function &F,
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100 FunctionAnalysisManager &AM) {
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101 bool Changed = eliminateUnreachableBlock(F);
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102 if (!Changed)
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103 return PreservedAnalyses::all();
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104 PreservedAnalyses PA;
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105 PA.preserve<DominatorTreeAnalysis>();
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106 return PA;
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107 }
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108
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109 namespace {
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110 class UnreachableMachineBlockElim : public MachineFunctionPass {
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111 bool runOnMachineFunction(MachineFunction &F) override;
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112 void getAnalysisUsage(AnalysisUsage &AU) const override;
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113 MachineModuleInfo *MMI;
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114 public:
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115 static char ID; // Pass identification, replacement for typeid
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116 UnreachableMachineBlockElim() : MachineFunctionPass(ID) {}
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117 };
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118 }
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119 char UnreachableMachineBlockElim::ID = 0;
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120
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121 INITIALIZE_PASS(UnreachableMachineBlockElim, "unreachable-mbb-elimination",
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122 "Remove unreachable machine basic blocks", false, false)
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123
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124 char &llvm::UnreachableMachineBlockElimID = UnreachableMachineBlockElim::ID;
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125
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126 void UnreachableMachineBlockElim::getAnalysisUsage(AnalysisUsage &AU) const {
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127 AU.addPreserved<MachineLoopInfo>();
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128 AU.addPreserved<MachineDominatorTree>();
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129 MachineFunctionPass::getAnalysisUsage(AU);
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130 }
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131
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132 bool UnreachableMachineBlockElim::runOnMachineFunction(MachineFunction &F) {
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133 df_iterator_default_set<MachineBasicBlock*> Reachable;
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134 bool ModifiedPHI = false;
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135
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136 MMI = getAnalysisIfAvailable<MachineModuleInfo>();
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137 MachineDominatorTree *MDT = getAnalysisIfAvailable<MachineDominatorTree>();
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138 MachineLoopInfo *MLI = getAnalysisIfAvailable<MachineLoopInfo>();
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139
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140 // Mark all reachable blocks.
77
54457678186b LLVM 3.6
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents: 0
diff changeset
141 for (MachineBasicBlock *BB : depth_first_ext(&F, Reachable))
54457678186b LLVM 3.6
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parents: 0
diff changeset
142 (void)BB/* Mark all reachable blocks */;
0
95c75e76d11b LLVM 3.4
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parents:
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143
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parents:
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144 // Loop over all dead blocks, remembering them and deleting all instructions
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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145 // in them.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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146 std::vector<MachineBasicBlock*> DeadBlocks;
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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147 for (MachineFunction::iterator I = F.begin(), E = F.end(); I != E; ++I) {
95
afa8332a0e37 LLVM 3.8
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parents: 83
diff changeset
148 MachineBasicBlock *BB = &*I;
0
95c75e76d11b LLVM 3.4
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149
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150 // Test for deadness.
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
151 if (!Reachable.count(BB)) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
152 DeadBlocks.push_back(BB);
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153
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parents:
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154 // Update dominator and loop info.
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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155 if (MLI) MLI->removeBlock(BB);
95c75e76d11b LLVM 3.4
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parents:
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156 if (MDT && MDT->getNode(BB)) MDT->eraseNode(BB);
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
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157
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
158 while (BB->succ_begin() != BB->succ_end()) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
159 MachineBasicBlock* succ = *BB->succ_begin();
95c75e76d11b LLVM 3.4
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parents:
diff changeset
160
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
161 MachineBasicBlock::iterator start = succ->begin();
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
162 while (start != succ->end() && start->isPHI()) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
163 for (unsigned i = start->getNumOperands() - 1; i >= 2; i-=2)
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
164 if (start->getOperand(i).isMBB() &&
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
165 start->getOperand(i).getMBB() == BB) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
166 start->RemoveOperand(i);
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
167 start->RemoveOperand(i-1);
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
168 }
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
169
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
170 start++;
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
171 }
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
172
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
173 BB->removeSuccessor(BB->succ_begin());
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parents:
diff changeset
174 }
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
175 }
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
176 }
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
177
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
178 // Actually remove the blocks now.
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parents:
diff changeset
179 for (unsigned i = 0, e = DeadBlocks.size(); i != e; ++i)
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
180 DeadBlocks[i]->eraseFromParent();
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parents:
diff changeset
181
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parents:
diff changeset
182 // Cleanup PHI nodes.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
183 for (MachineFunction::iterator I = F.begin(), E = F.end(); I != E; ++I) {
95
afa8332a0e37 LLVM 3.8
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parents: 83
diff changeset
184 MachineBasicBlock *BB = &*I;
0
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
185 // Prune unneeded PHI entries.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
186 SmallPtrSet<MachineBasicBlock*, 8> preds(BB->pred_begin(),
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
187 BB->pred_end());
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
188 MachineBasicBlock::iterator phi = BB->begin();
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
189 while (phi != BB->end() && phi->isPHI()) {
95c75e76d11b LLVM 3.4
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parents:
diff changeset
190 for (unsigned i = phi->getNumOperands() - 1; i >= 2; i-=2)
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
191 if (!preds.count(phi->getOperand(i).getMBB())) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
192 phi->RemoveOperand(i);
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
193 phi->RemoveOperand(i-1);
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
194 ModifiedPHI = true;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
195 }
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
196
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
197 if (phi->getNumOperands() == 3) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
198 unsigned Input = phi->getOperand(1).getReg();
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
199 unsigned Output = phi->getOperand(0).getReg();
95c75e76d11b LLVM 3.4
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parents:
diff changeset
200
120
1172e4bd9c6f update 4.0.0
mir3636
parents: 95
diff changeset
201 phi++->eraseFromParent();
0
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
202 ModifiedPHI = true;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
203
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
204 if (Input != Output) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
205 MachineRegisterInfo &MRI = F.getRegInfo();
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
206 MRI.constrainRegClass(Input, MRI.getRegClass(Output));
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
207 MRI.replaceRegWith(Output, Input);
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
208 }
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
209
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
210 continue;
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 ++phi;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
214 }
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
215 }
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
216
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
217 F.RenumberBlocks();
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
218
83
60c9769439b8 LLVM 3.7
Tatsuki IHA <e125716@ie.u-ryukyu.ac.jp>
parents: 77
diff changeset
219 return (!DeadBlocks.empty() || ModifiedPHI);
0
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
220 }