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1 //===- HexagonCFGOptimizer.cpp - CFG optimizations ------------------------===//
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2 //
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3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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4 // See https://llvm.org/LICENSE.txt for license information.
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5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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6 //
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7 //===----------------------------------------------------------------------===//
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8
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9 #include "Hexagon.h"
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207
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10 #include "MCTargetDesc/HexagonMCTargetDesc.h"
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150
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11 #include "llvm/CodeGen/MachineBasicBlock.h"
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12 #include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
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13 #include "llvm/CodeGen/MachineFunction.h"
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14 #include "llvm/CodeGen/MachineFunctionPass.h"
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15 #include "llvm/CodeGen/MachineInstr.h"
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16 #include "llvm/CodeGen/MachineOperand.h"
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17 #include "llvm/CodeGen/TargetInstrInfo.h"
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18 #include "llvm/CodeGen/TargetSubtargetInfo.h"
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19 #include "llvm/Pass.h"
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20 #include "llvm/Support/ErrorHandling.h"
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21 #include <cassert>
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22 #include <vector>
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23
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24 using namespace llvm;
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25
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26 #define DEBUG_TYPE "hexagon_cfg"
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27
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28 namespace llvm {
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29
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30 FunctionPass *createHexagonCFGOptimizer();
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31 void initializeHexagonCFGOptimizerPass(PassRegistry&);
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32
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33 } // end namespace llvm
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34
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35 namespace {
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36
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37 class HexagonCFGOptimizer : public MachineFunctionPass {
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38 private:
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39 void InvertAndChangeJumpTarget(MachineInstr &, MachineBasicBlock *);
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40 bool isOnFallThroughPath(MachineBasicBlock *MBB);
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41
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42 public:
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43 static char ID;
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44
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45 HexagonCFGOptimizer() : MachineFunctionPass(ID) {
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46 initializeHexagonCFGOptimizerPass(*PassRegistry::getPassRegistry());
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47 }
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48
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49 StringRef getPassName() const override { return "Hexagon CFG Optimizer"; }
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50 bool runOnMachineFunction(MachineFunction &Fn) override;
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51
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52 MachineFunctionProperties getRequiredProperties() const override {
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53 return MachineFunctionProperties().set(
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54 MachineFunctionProperties::Property::NoVRegs);
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55 }
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56 };
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57
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58 } // end anonymous namespace
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59
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60 char HexagonCFGOptimizer::ID = 0;
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61
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62 static bool IsConditionalBranch(int Opc) {
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63 switch (Opc) {
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64 case Hexagon::J2_jumpt:
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65 case Hexagon::J2_jumptpt:
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66 case Hexagon::J2_jumpf:
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67 case Hexagon::J2_jumpfpt:
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68 case Hexagon::J2_jumptnew:
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69 case Hexagon::J2_jumpfnew:
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70 case Hexagon::J2_jumptnewpt:
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71 case Hexagon::J2_jumpfnewpt:
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72 return true;
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73 }
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74 return false;
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75 }
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76
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77 static bool IsUnconditionalJump(int Opc) {
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78 return (Opc == Hexagon::J2_jump);
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79 }
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80
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81 void HexagonCFGOptimizer::InvertAndChangeJumpTarget(
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82 MachineInstr &MI, MachineBasicBlock *NewTarget) {
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83 const TargetInstrInfo *TII =
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84 MI.getParent()->getParent()->getSubtarget().getInstrInfo();
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85 int NewOpcode = 0;
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86 switch (MI.getOpcode()) {
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87 case Hexagon::J2_jumpt:
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88 NewOpcode = Hexagon::J2_jumpf;
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89 break;
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90 case Hexagon::J2_jumpf:
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91 NewOpcode = Hexagon::J2_jumpt;
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92 break;
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93 case Hexagon::J2_jumptnewpt:
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94 NewOpcode = Hexagon::J2_jumpfnewpt;
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95 break;
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96 case Hexagon::J2_jumpfnewpt:
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97 NewOpcode = Hexagon::J2_jumptnewpt;
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98 break;
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99 default:
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100 llvm_unreachable("Cannot handle this case");
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101 }
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102
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103 MI.setDesc(TII->get(NewOpcode));
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104 MI.getOperand(1).setMBB(NewTarget);
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105 }
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106
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107 bool HexagonCFGOptimizer::isOnFallThroughPath(MachineBasicBlock *MBB) {
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108 if (MBB->canFallThrough())
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109 return true;
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110 for (MachineBasicBlock *PB : MBB->predecessors())
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111 if (PB->isLayoutSuccessor(MBB) && PB->canFallThrough())
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112 return true;
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113 return false;
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114 }
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115
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116 bool HexagonCFGOptimizer::runOnMachineFunction(MachineFunction &Fn) {
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117 if (skipFunction(Fn.getFunction()))
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118 return false;
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119
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120 // Loop over all of the basic blocks.
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121 for (MachineFunction::iterator MBBb = Fn.begin(), MBBe = Fn.end();
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122 MBBb != MBBe; ++MBBb) {
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123 MachineBasicBlock *MBB = &*MBBb;
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124
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125 // Traverse the basic block.
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126 MachineBasicBlock::iterator MII = MBB->getFirstTerminator();
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127 if (MII != MBB->end()) {
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128 MachineInstr &MI = *MII;
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129 int Opc = MI.getOpcode();
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130 if (IsConditionalBranch(Opc)) {
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131 // (Case 1) Transform the code if the following condition occurs:
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132 // BB1: if (p0) jump BB3
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133 // ...falls-through to BB2 ...
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134 // BB2: jump BB4
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135 // ...next block in layout is BB3...
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136 // BB3: ...
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137 //
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138 // Transform this to:
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139 // BB1: if (!p0) jump BB4
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140 // Remove BB2
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141 // BB3: ...
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142 //
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143 // (Case 2) A variation occurs when BB3 contains a JMP to BB4:
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144 // BB1: if (p0) jump BB3
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145 // ...falls-through to BB2 ...
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146 // BB2: jump BB4
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147 // ...other basic blocks ...
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148 // BB4:
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149 // ...not a fall-thru
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150 // BB3: ...
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151 // jump BB4
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152 //
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153 // Transform this to:
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154 // BB1: if (!p0) jump BB4
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155 // Remove BB2
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156 // BB3: ...
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157 // BB4: ...
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158 unsigned NumSuccs = MBB->succ_size();
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159 MachineBasicBlock::succ_iterator SI = MBB->succ_begin();
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160 MachineBasicBlock* FirstSucc = *SI;
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161 MachineBasicBlock* SecondSucc = *(++SI);
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162 MachineBasicBlock* LayoutSucc = nullptr;
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163 MachineBasicBlock* JumpAroundTarget = nullptr;
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164
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165 if (MBB->isLayoutSuccessor(FirstSucc)) {
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166 LayoutSucc = FirstSucc;
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167 JumpAroundTarget = SecondSucc;
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168 } else if (MBB->isLayoutSuccessor(SecondSucc)) {
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169 LayoutSucc = SecondSucc;
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170 JumpAroundTarget = FirstSucc;
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171 } else {
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172 // Odd case...cannot handle.
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173 }
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174
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175 // The target of the unconditional branch must be JumpAroundTarget.
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176 // TODO: If not, we should not invert the unconditional branch.
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177 MachineBasicBlock* CondBranchTarget = nullptr;
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178 if (MI.getOpcode() == Hexagon::J2_jumpt ||
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179 MI.getOpcode() == Hexagon::J2_jumpf) {
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180 CondBranchTarget = MI.getOperand(1).getMBB();
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181 }
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182
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183 if (!LayoutSucc || (CondBranchTarget != JumpAroundTarget)) {
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184 continue;
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185 }
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186
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187 if ((NumSuccs == 2) && LayoutSucc && (LayoutSucc->pred_size() == 1)) {
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188 // Ensure that BB2 has one instruction -- an unconditional jump.
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189 if ((LayoutSucc->size() == 1) &&
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190 IsUnconditionalJump(LayoutSucc->front().getOpcode())) {
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191 assert(JumpAroundTarget && "jump target is needed to process second basic block");
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192 MachineBasicBlock* UncondTarget =
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193 LayoutSucc->front().getOperand(0).getMBB();
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194 // Check if the layout successor of BB2 is BB3.
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195 bool case1 = LayoutSucc->isLayoutSuccessor(JumpAroundTarget);
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196 bool case2 = JumpAroundTarget->isSuccessor(UncondTarget) &&
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197 !JumpAroundTarget->empty() &&
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198 IsUnconditionalJump(JumpAroundTarget->back().getOpcode()) &&
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199 JumpAroundTarget->pred_size() == 1 &&
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200 JumpAroundTarget->succ_size() == 1;
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201
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202 if (case1 || case2) {
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203 InvertAndChangeJumpTarget(MI, UncondTarget);
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204 MBB->replaceSuccessor(JumpAroundTarget, UncondTarget);
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205
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206 // Remove the unconditional branch in LayoutSucc.
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207 LayoutSucc->erase(LayoutSucc->begin());
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208 LayoutSucc->replaceSuccessor(UncondTarget, JumpAroundTarget);
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209
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210 // This code performs the conversion for case 2, which moves
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211 // the block to the fall-thru case (BB3 in the code above).
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212 if (case2 && !case1) {
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213 JumpAroundTarget->moveAfter(LayoutSucc);
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214 // only move a block if it doesn't have a fall-thru. otherwise
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215 // the CFG will be incorrect.
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216 if (!isOnFallThroughPath(UncondTarget))
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217 UncondTarget->moveAfter(JumpAroundTarget);
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218 }
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219
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220 // Correct live-in information. Is used by post-RA scheduler
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221 // The live-in to LayoutSucc is now all values live-in to
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222 // JumpAroundTarget.
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223 std::vector<MachineBasicBlock::RegisterMaskPair> OrigLiveIn(
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224 LayoutSucc->livein_begin(), LayoutSucc->livein_end());
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225 std::vector<MachineBasicBlock::RegisterMaskPair> NewLiveIn(
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226 JumpAroundTarget->livein_begin(),
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227 JumpAroundTarget->livein_end());
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228 for (const auto &OrigLI : OrigLiveIn)
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229 LayoutSucc->removeLiveIn(OrigLI.PhysReg);
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230 for (const auto &NewLI : NewLiveIn)
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231 LayoutSucc->addLiveIn(NewLI);
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232 }
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233 }
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234 }
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235 }
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236 }
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237 }
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238 return true;
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239 }
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240
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241 //===----------------------------------------------------------------------===//
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242 // Public Constructor Functions
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243 //===----------------------------------------------------------------------===//
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244
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245 INITIALIZE_PASS(HexagonCFGOptimizer, "hexagon-cfg", "Hexagon CFG Optimizer",
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246 false, false)
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247
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248 FunctionPass *llvm::createHexagonCFGOptimizer() {
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249 return new HexagonCFGOptimizer();
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250 }
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