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annotate lib/Target/X86/X86PadShortFunction.cpp @ 116:a609e5c42ecc

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change from CGF to this
author mir3636
date Mon, 08 Aug 2016 19:47:00 +0900
parents 7d135dc70f03
children 1172e4bd9c6f
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1 //===-------- X86PadShortFunction.cpp - pad short functions -----------===//
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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 file defines the pass which will pad short functions to prevent
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11 // a stall if a function returns before the return address is ready. This
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12 // is needed for some Intel Atom processors.
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13 //
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14 //===----------------------------------------------------------------------===//
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15
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16 #include <algorithm>
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17
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18 #include "X86.h"
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19 #include "X86InstrInfo.h"
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20 #include "X86Subtarget.h"
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21 #include "llvm/ADT/Statistic.h"
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22 #include "llvm/CodeGen/MachineFunctionPass.h"
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23 #include "llvm/CodeGen/MachineInstrBuilder.h"
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24 #include "llvm/CodeGen/MachineRegisterInfo.h"
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25 #include "llvm/CodeGen/Passes.h"
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26 #include "llvm/IR/Function.h"
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27 #include "llvm/Support/Debug.h"
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28 #include "llvm/Support/raw_ostream.h"
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29 #include "llvm/Target/TargetInstrInfo.h"
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30
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31 using namespace llvm;
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32
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33 #define DEBUG_TYPE "x86-pad-short-functions"
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34
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35 STATISTIC(NumBBsPadded, "Number of basic blocks padded");
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36
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37 namespace {
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38 struct VisitedBBInfo {
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39 // HasReturn - Whether the BB contains a return instruction
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40 bool HasReturn;
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41
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42 // Cycles - Number of cycles until return if HasReturn is true, otherwise
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43 // number of cycles until end of the BB
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44 unsigned int Cycles;
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45
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46 VisitedBBInfo() : HasReturn(false), Cycles(0) {}
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47 VisitedBBInfo(bool HasReturn, unsigned int Cycles)
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48 : HasReturn(HasReturn), Cycles(Cycles) {}
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49 };
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50
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51 struct PadShortFunc : public MachineFunctionPass {
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52 static char ID;
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53 PadShortFunc() : MachineFunctionPass(ID)
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54 , Threshold(4), STI(nullptr), TII(nullptr) {}
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55
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56 bool runOnMachineFunction(MachineFunction &MF) override;
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57
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58 const char *getPassName() const override {
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59 return "X86 Atom pad short functions";
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60 }
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61
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62 private:
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63 void findReturns(MachineBasicBlock *MBB,
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64 unsigned int Cycles = 0);
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65
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66 bool cyclesUntilReturn(MachineBasicBlock *MBB,
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67 unsigned int &Cycles);
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68
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69 void addPadding(MachineBasicBlock *MBB,
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70 MachineBasicBlock::iterator &MBBI,
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71 unsigned int NOOPsToAdd);
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72
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73 const unsigned int Threshold;
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74
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75 // ReturnBBs - Maps basic blocks that return to the minimum number of
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76 // cycles until the return, starting from the entry block.
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77 DenseMap<MachineBasicBlock*, unsigned int> ReturnBBs;
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78
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79 // VisitedBBs - Cache of previously visited BBs.
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80 DenseMap<MachineBasicBlock*, VisitedBBInfo> VisitedBBs;
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81
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82 const X86Subtarget *STI;
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83 const TargetInstrInfo *TII;
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84 };
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85
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86 char PadShortFunc::ID = 0;
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87 }
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89 FunctionPass *llvm::createX86PadShortFunctions() {
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90 return new PadShortFunc();
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91 }
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92
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93 /// runOnMachineFunction - Loop over all of the basic blocks, inserting
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94 /// NOOP instructions before early exits.
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95 bool PadShortFunc::runOnMachineFunction(MachineFunction &MF) {
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96 if (MF.getFunction()->optForSize()) {
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97 return false;
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98 }
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99
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100 STI = &MF.getSubtarget<X86Subtarget>();
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101 if (!STI->padShortFunctions())
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102 return false;
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103
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104 TII = STI->getInstrInfo();
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105
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106 // Search through basic blocks and mark the ones that have early returns
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107 ReturnBBs.clear();
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108 VisitedBBs.clear();
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109 findReturns(&MF.front());
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110
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111 bool MadeChange = false;
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112
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113 MachineBasicBlock *MBB;
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114 unsigned int Cycles = 0;
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115
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116 // Pad the identified basic blocks with NOOPs
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117 for (DenseMap<MachineBasicBlock*, unsigned int>::iterator I = ReturnBBs.begin();
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118 I != ReturnBBs.end(); ++I) {
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119 MBB = I->first;
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120 Cycles = I->second;
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121
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122 if (Cycles < Threshold) {
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123 // BB ends in a return. Skip over any DBG_VALUE instructions
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124 // trailing the terminator.
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125 assert(MBB->size() > 0 &&
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126 "Basic block should contain at least a RET but is empty");
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127 MachineBasicBlock::iterator ReturnLoc = --MBB->end();
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128
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129 while (ReturnLoc->isDebugValue())
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130 --ReturnLoc;
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131 assert(ReturnLoc->isReturn() && !ReturnLoc->isCall() &&
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132 "Basic block does not end with RET");
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
133
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
134 addPadding(MBB, ReturnLoc, Threshold - Cycles);
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
135 NumBBsPadded++;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
136 MadeChange = true;
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 }
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
139
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
140 return MadeChange;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
141 }
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
142
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
143 /// findReturn - Starting at MBB, follow control flow and add all
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
144 /// basic blocks that contain a return to ReturnBBs.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
145 void PadShortFunc::findReturns(MachineBasicBlock *MBB, unsigned int Cycles) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
146 // If this BB has a return, note how many cycles it takes to get there.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
147 bool hasReturn = cyclesUntilReturn(MBB, Cycles);
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
148 if (Cycles >= Threshold)
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
149 return;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
150
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
151 if (hasReturn) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
152 ReturnBBs[MBB] = std::max(ReturnBBs[MBB], Cycles);
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
153 return;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
154 }
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
155
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
156 // Follow branches in BB and look for returns
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
157 for (MachineBasicBlock::succ_iterator I = MBB->succ_begin();
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
158 I != MBB->succ_end(); ++I) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
159 if (*I == MBB)
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
160 continue;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
161 findReturns(*I, Cycles);
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
162 }
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
163 }
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
164
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
165 /// cyclesUntilReturn - return true if the MBB has a return instruction,
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
166 /// and return false otherwise.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
167 /// Cycles will be incremented by the number of cycles taken to reach the
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
168 /// return or the end of the BB, whichever occurs first.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
169 bool PadShortFunc::cyclesUntilReturn(MachineBasicBlock *MBB,
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
170 unsigned int &Cycles) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
171 // Return cached result if BB was previously visited
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
172 DenseMap<MachineBasicBlock*, VisitedBBInfo>::iterator it
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
173 = VisitedBBs.find(MBB);
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
174 if (it != VisitedBBs.end()) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
175 VisitedBBInfo BBInfo = it->second;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
176 Cycles += BBInfo.Cycles;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
177 return BBInfo.HasReturn;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
178 }
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
179
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
180 unsigned int CyclesToEnd = 0;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
181
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
182 for (MachineBasicBlock::iterator MBBI = MBB->begin();
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
183 MBBI != MBB->end(); ++MBBI) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
184 MachineInstr *MI = MBBI;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
185 // Mark basic blocks with a return instruction. Calls to other
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
186 // functions do not count because the called function will be padded,
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
187 // if necessary.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
188 if (MI->isReturn() && !MI->isCall()) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
189 VisitedBBs[MBB] = VisitedBBInfo(true, CyclesToEnd);
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
190 Cycles += CyclesToEnd;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
191 return true;
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
83
60c9769439b8 LLVM 3.7
Tatsuki IHA <e125716@ie.u-ryukyu.ac.jp>
parents: 77
diff changeset
194 CyclesToEnd += TII->getInstrLatency(STI->getInstrItineraryData(), MI);
0
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
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
197 VisitedBBs[MBB] = VisitedBBInfo(false, CyclesToEnd);
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
198 Cycles += CyclesToEnd;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
199 return false;
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
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
202 /// addPadding - Add the given number of NOOP instructions to the function
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
203 /// just prior to the return at MBBI
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
204 void PadShortFunc::addPadding(MachineBasicBlock *MBB,
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
205 MachineBasicBlock::iterator &MBBI,
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
206 unsigned int NOOPsToAdd) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
207 DebugLoc DL = MBBI->getDebugLoc();
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 while (NOOPsToAdd-- > 0) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
210 BuildMI(*MBB, MBBI, DL, TII->get(X86::NOOP));
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
211 BuildMI(*MBB, MBBI, DL, TII->get(X86::NOOP));
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 }