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annotate lib/Transforms/IPO/ConstantMerge.cpp @ 125:56c5119fbcd2

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fix
author mir3636
date Sun, 03 Dec 2017 20:09:16 +0900
parents 803732b1fca8
children c2174574ed3a
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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1 //===- ConstantMerge.cpp - Merge duplicate global constants ---------------===//
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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 interface to a pass that merges duplicate global
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11 // constants together into a single constant that is shared. This is useful
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12 // because some passes (ie TraceValues) insert a lot of string constants into
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13 // the program, regardless of whether or not an existing string is available.
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14 //
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15 // Algorithm: ConstantMerge is designed to build up a map of available constants
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16 // and eliminate duplicates when it is initialized.
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17 //
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18 //===----------------------------------------------------------------------===//
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19
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20 #include "llvm/Transforms/IPO/ConstantMerge.h"
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21 #include "llvm/ADT/DenseMap.h"
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22 #include "llvm/ADT/SmallPtrSet.h"
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23 #include "llvm/ADT/SmallVector.h"
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24 #include "llvm/ADT/Statistic.h"
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25 #include "llvm/IR/Constants.h"
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26 #include "llvm/IR/DataLayout.h"
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27 #include "llvm/IR/DerivedTypes.h"
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28 #include "llvm/IR/GlobalValue.h"
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29 #include "llvm/IR/GlobalVariable.h"
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30 #include "llvm/IR/LLVMContext.h"
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31 #include "llvm/IR/Module.h"
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32 #include "llvm/Pass.h"
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33 #include "llvm/Support/Casting.h"
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34 #include "llvm/Transforms/IPO.h"
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35 #include <algorithm>
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36 #include <cassert>
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37 #include <utility>
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38
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39 using namespace llvm;
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40
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41 #define DEBUG_TYPE "constmerge"
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42
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43 STATISTIC(NumMerged, "Number of global constants merged");
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44
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45 /// Find values that are marked as llvm.used.
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46 static void FindUsedValues(GlobalVariable *LLVMUsed,
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47 SmallPtrSetImpl<const GlobalValue*> &UsedValues) {
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48 if (!LLVMUsed) return;
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49 ConstantArray *Inits = cast<ConstantArray>(LLVMUsed->getInitializer());
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50
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51 for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i) {
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52 Value *Operand = Inits->getOperand(i)->stripPointerCastsNoFollowAliases();
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53 GlobalValue *GV = cast<GlobalValue>(Operand);
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54 UsedValues.insert(GV);
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55 }
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56 }
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57
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58 // True if A is better than B.
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59 static bool IsBetterCanonical(const GlobalVariable &A,
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60 const GlobalVariable &B) {
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61 if (!A.hasLocalLinkage() && B.hasLocalLinkage())
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62 return true;
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63
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64 if (A.hasLocalLinkage() && !B.hasLocalLinkage())
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65 return false;
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66
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67 return A.hasGlobalUnnamedAddr();
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68 }
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69
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70 static bool hasMetadataOtherThanDebugLoc(const GlobalVariable *GV) {
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71 SmallVector<std::pair<unsigned, MDNode *>, 4> MDs;
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72 GV->getAllMetadata(MDs);
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73 for (const auto &V : MDs)
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74 if (V.first != LLVMContext::MD_dbg)
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75 return true;
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76 return false;
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77 }
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78
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79 static void copyDebugLocMetadata(const GlobalVariable *From,
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80 GlobalVariable *To) {
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81 SmallVector<DIGlobalVariableExpression *, 1> MDs;
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82 From->getDebugInfo(MDs);
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83 for (auto MD : MDs)
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84 To->addDebugInfo(MD);
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85 }
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86
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87 static unsigned getAlignment(GlobalVariable *GV) {
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88 unsigned Align = GV->getAlignment();
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89 if (Align)
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90 return Align;
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91 return GV->getParent()->getDataLayout().getPreferredAlignment(GV);
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92 }
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93
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94 static bool mergeConstants(Module &M) {
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95 // Find all the globals that are marked "used". These cannot be merged.
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96 SmallPtrSet<const GlobalValue*, 8> UsedGlobals;
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97 FindUsedValues(M.getGlobalVariable("llvm.used"), UsedGlobals);
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98 FindUsedValues(M.getGlobalVariable("llvm.compiler.used"), UsedGlobals);
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99
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100 // Map unique constants to globals.
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101 DenseMap<Constant *, GlobalVariable *> CMap;
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102
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103 // Replacements - This vector contains a list of replacements to perform.
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104 SmallVector<std::pair<GlobalVariable*, GlobalVariable*>, 32> Replacements;
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105
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106 bool MadeChange = false;
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107
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108 // Iterate constant merging while we are still making progress. Merging two
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109 // constants together may allow us to merge other constants together if the
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110 // second level constants have initializers which point to the globals that
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111 // were just merged.
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112 while (true) {
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113 // First: Find the canonical constants others will be merged with.
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114 for (Module::global_iterator GVI = M.global_begin(), E = M.global_end();
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115 GVI != E; ) {
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116 GlobalVariable *GV = &*GVI++;
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117
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118 // If this GV is dead, remove it.
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119 GV->removeDeadConstantUsers();
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120 if (GV->use_empty() && GV->hasLocalLinkage()) {
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121 GV->eraseFromParent();
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122 continue;
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123 }
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124
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125 // Only process constants with initializers in the default address space.
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126 if (!GV->isConstant() || !GV->hasDefinitiveInitializer() ||
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127 GV->getType()->getAddressSpace() != 0 || GV->hasSection() ||
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128 // Don't touch values marked with attribute(used).
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129 UsedGlobals.count(GV))
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130 continue;
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131
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132 // This transformation is legal for weak ODR globals in the sense it
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133 // doesn't change semantics, but we really don't want to perform it
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134 // anyway; it's likely to pessimize code generation, and some tools
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135 // (like the Darwin linker in cases involving CFString) don't expect it.
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136 if (GV->isWeakForLinker())
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137 continue;
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138
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139 // Don't touch globals with metadata other then !dbg.
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140 if (hasMetadataOtherThanDebugLoc(GV))
803732b1fca8 LLVM 5.0
kono
parents: 120
diff changeset
141 continue;
803732b1fca8 LLVM 5.0
kono
parents: 120
diff changeset
142
0
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
143 Constant *Init = GV->getInitializer();
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
144
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
145 // Check to see if the initializer is already known.
95
afa8332a0e37 LLVM 3.8
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents: 77
diff changeset
146 GlobalVariable *&Slot = CMap[Init];
0
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
147
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
148 // If this is the first constant we find or if the old one is local,
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
149 // replace with the current one. If the current is externally visible
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
150 // it cannot be replace, but can be the canonical constant we merge with.
77
54457678186b LLVM 3.6
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents: 0
diff changeset
151 if (!Slot || IsBetterCanonical(*GV, *Slot))
0
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
152 Slot = GV;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
153 }
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 // Second: identify all globals that can be merged together, filling in
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
156 // the Replacements vector. We cannot do the replacement in this pass
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
157 // because doing so may cause initializers of other globals to be rewritten,
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
158 // invalidating the Constant* pointers in CMap.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
159 for (Module::global_iterator GVI = M.global_begin(), E = M.global_end();
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
160 GVI != E; ) {
100
7d135dc70f03 LLVM 3.9
Miyagi Mitsuki <e135756@ie.u-ryukyu.ac.jp>
parents: 95
diff changeset
161 GlobalVariable *GV = &*GVI++;
0
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 // Only process constants with initializers in the default address space.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
164 if (!GV->isConstant() || !GV->hasDefinitiveInitializer() ||
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
165 GV->getType()->getAddressSpace() != 0 || GV->hasSection() ||
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
166 // Don't touch values marked with attribute(used).
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
167 UsedGlobals.count(GV))
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
168 continue;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
169
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
170 // We can only replace constant with local linkage.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
171 if (!GV->hasLocalLinkage())
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
172 continue;
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 Constant *Init = GV->getInitializer();
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 // Check to see if the initializer is already known.
95
afa8332a0e37 LLVM 3.8
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents: 77
diff changeset
177 GlobalVariable *Slot = CMap[Init];
0
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 if (!Slot || Slot == GV)
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
180 continue;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
181
120
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
182 if (!Slot->hasGlobalUnnamedAddr() && !GV->hasGlobalUnnamedAddr())
0
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
183 continue;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
184
121
803732b1fca8 LLVM 5.0
kono
parents: 120
diff changeset
185 if (hasMetadataOtherThanDebugLoc(GV))
803732b1fca8 LLVM 5.0
kono
parents: 120
diff changeset
186 continue;
803732b1fca8 LLVM 5.0
kono
parents: 120
diff changeset
187
120
1172e4bd9c6f update 4.0.0
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parents: 100
diff changeset
188 if (!GV->hasGlobalUnnamedAddr())
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
189 Slot->setUnnamedAddr(GlobalValue::UnnamedAddr::None);
0
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 // Make all uses of the duplicate constant use the canonical version.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
192 Replacements.push_back(std::make_pair(GV, Slot));
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
193 }
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
194
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
195 if (Replacements.empty())
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
196 return MadeChange;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
197 CMap.clear();
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
198
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
199 // Now that we have figured out which replacements must be made, do them all
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
200 // now. This avoid invalidating the pointers in CMap, which are unneeded
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
201 // now.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
202 for (unsigned i = 0, e = Replacements.size(); i != e; ++i) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
203 // Bump the alignment if necessary.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
204 if (Replacements[i].first->getAlignment() ||
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
205 Replacements[i].second->getAlignment()) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
206 Replacements[i].second->setAlignment(
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
207 std::max(getAlignment(Replacements[i].first),
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
208 getAlignment(Replacements[i].second)));
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
121
803732b1fca8 LLVM 5.0
kono
parents: 120
diff changeset
211 copyDebugLocMetadata(Replacements[i].first, Replacements[i].second);
803732b1fca8 LLVM 5.0
kono
parents: 120
diff changeset
212
0
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
213 // Eliminate any uses of the dead global.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
214 Replacements[i].first->replaceAllUsesWith(Replacements[i].second);
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 // Delete the global value from the module.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
217 assert(Replacements[i].first->hasLocalLinkage() &&
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
218 "Refusing to delete an externally visible global variable.");
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
219 Replacements[i].first->eraseFromParent();
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
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
222 NumMerged += Replacements.size();
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
223 Replacements.clear();
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 }
120
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
226
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
227 PreservedAnalyses ConstantMergePass::run(Module &M, ModuleAnalysisManager &) {
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
228 if (!mergeConstants(M))
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
229 return PreservedAnalyses::all();
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
230 return PreservedAnalyses::none();
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
231 }
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
232
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
233 namespace {
121
803732b1fca8 LLVM 5.0
kono
parents: 120
diff changeset
234
120
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
235 struct ConstantMergeLegacyPass : public ModulePass {
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
236 static char ID; // Pass identification, replacement for typeid
121
803732b1fca8 LLVM 5.0
kono
parents: 120
diff changeset
237
120
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
238 ConstantMergeLegacyPass() : ModulePass(ID) {
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
239 initializeConstantMergeLegacyPassPass(*PassRegistry::getPassRegistry());
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
240 }
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
241
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
242 // For this pass, process all of the globals in the module, eliminating
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
243 // duplicate constants.
121
803732b1fca8 LLVM 5.0
kono
parents: 120
diff changeset
244 bool runOnModule(Module &M) override {
120
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
245 if (skipModule(M))
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
246 return false;
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
247 return mergeConstants(M);
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
248 }
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
249 };
121
803732b1fca8 LLVM 5.0
kono
parents: 120
diff changeset
250
803732b1fca8 LLVM 5.0
kono
parents: 120
diff changeset
251 } // end anonymous namespace
120
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
252
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
253 char ConstantMergeLegacyPass::ID = 0;
121
803732b1fca8 LLVM 5.0
kono
parents: 120
diff changeset
254
120
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
255 INITIALIZE_PASS(ConstantMergeLegacyPass, "constmerge",
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
256 "Merge Duplicate Global Constants", false, false)
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
257
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
258 ModulePass *llvm::createConstantMergePass() {
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
259 return new ConstantMergeLegacyPass();
1172e4bd9c6f update 4.0.0
mir3636
parents: 100
diff changeset
260 }