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annotate lib/Transforms/IPO/ConstantMerge.cpp @ 83:60c9769439b8 LLVM3.7

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LLVM 3.7
author Tatsuki IHA <e125716@ie.u-ryukyu.ac.jp>
date Wed, 18 Feb 2015 14:55:36 +0900
parents 54457678186b
children afa8332a0e37
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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.h"
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21 #include "llvm/ADT/DenseMap.h"
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22 #include "llvm/ADT/PointerIntPair.h"
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23 #include "llvm/ADT/SmallPtrSet.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/Module.h"
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29 #include "llvm/IR/Operator.h"
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30 #include "llvm/Pass.h"
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31 using namespace llvm;
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32
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33 #define DEBUG_TYPE "constmerge"
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34
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35 STATISTIC(NumMerged, "Number of global constants merged");
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36
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37 namespace {
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38 struct ConstantMerge : public ModulePass {
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39 static char ID; // Pass identification, replacement for typeid
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40 ConstantMerge() : ModulePass(ID) {
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41 initializeConstantMergePass(*PassRegistry::getPassRegistry());
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42 }
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43
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44 // For this pass, process all of the globals in the module, eliminating
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45 // duplicate constants.
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46 bool runOnModule(Module &M) override;
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47
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48 // Return true iff we can determine the alignment of this global variable.
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49 bool hasKnownAlignment(GlobalVariable *GV) const;
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50
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51 // Return the alignment of the global, including converting the default
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52 // alignment to a concrete value.
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53 unsigned getAlignment(GlobalVariable *GV) const;
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54
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55 const DataLayout *DL;
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56 };
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57 }
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58
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59 char ConstantMerge::ID = 0;
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60 INITIALIZE_PASS(ConstantMerge, "constmerge",
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61 "Merge Duplicate Global Constants", false, false)
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62
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63 ModulePass *llvm::createConstantMergePass() { return new ConstantMerge(); }
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64
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66
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67 /// Find values that are marked as llvm.used.
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68 static void FindUsedValues(GlobalVariable *LLVMUsed,
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69 SmallPtrSetImpl<const GlobalValue*> &UsedValues) {
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70 if (!LLVMUsed) return;
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71 ConstantArray *Inits = cast<ConstantArray>(LLVMUsed->getInitializer());
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72
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73 for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i) {
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74 Value *Operand = Inits->getOperand(i)->stripPointerCastsNoFollowAliases();
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75 GlobalValue *GV = cast<GlobalValue>(Operand);
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76 UsedValues.insert(GV);
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77 }
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78 }
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79
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80 // True if A is better than B.
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81 static bool IsBetterCanonical(const GlobalVariable &A,
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82 const GlobalVariable &B) {
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83 if (!A.hasLocalLinkage() && B.hasLocalLinkage())
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84 return true;
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85
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86 if (A.hasLocalLinkage() && !B.hasLocalLinkage())
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87 return false;
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88
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89 return A.hasUnnamedAddr();
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90 }
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91
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92 bool ConstantMerge::hasKnownAlignment(GlobalVariable *GV) const {
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93 return DL || GV->getAlignment() != 0;
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94 }
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95
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96 unsigned ConstantMerge::getAlignment(GlobalVariable *GV) const {
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97 unsigned Align = GV->getAlignment();
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98 if (Align)
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99 return Align;
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100 if (DL)
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101 return DL->getPreferredAlignment(GV);
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102 return 0;
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103 }
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104
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105 bool ConstantMerge::runOnModule(Module &M) {
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106 DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
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107 DL = DLP ? &DLP->getDataLayout() : nullptr;
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108
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109 // Find all the globals that are marked "used". These cannot be merged.
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110 SmallPtrSet<const GlobalValue*, 8> UsedGlobals;
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111 FindUsedValues(M.getGlobalVariable("llvm.used"), UsedGlobals);
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112 FindUsedValues(M.getGlobalVariable("llvm.compiler.used"), UsedGlobals);
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113
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114 // Map unique <constants, has-unknown-alignment> pairs to globals. We don't
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115 // want to merge globals of unknown alignment with those of explicit
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116 // alignment. If we have DataLayout, we always know the alignment.
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117 DenseMap<PointerIntPair<Constant*, 1, bool>, GlobalVariable*> CMap;
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118
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119 // Replacements - This vector contains a list of replacements to perform.
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120 SmallVector<std::pair<GlobalVariable*, GlobalVariable*>, 32> Replacements;
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121
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122 bool MadeChange = false;
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123
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124 // Iterate constant merging while we are still making progress. Merging two
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125 // constants together may allow us to merge other constants together if the
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126 // second level constants have initializers which point to the globals that
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127 // were just merged.
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128 while (1) {
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129
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130 // First: Find the canonical constants others will be merged with.
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
131 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
132 GVI != E; ) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
133 GlobalVariable *GV = GVI++;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
134
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
135 // If this GV is dead, remove it.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
136 GV->removeDeadConstantUsers();
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
137 if (GV->use_empty() && GV->hasLocalLinkage()) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
138 GV->eraseFromParent();
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
139 continue;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
140 }
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 // 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
143 if (!GV->isConstant() || !GV->hasDefinitiveInitializer() ||
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
144 GV->getType()->getAddressSpace() != 0 || GV->hasSection() ||
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
145 // Don't touch values marked with attribute(used).
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
146 UsedGlobals.count(GV))
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
147 continue;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
148
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
149 // This transformation is legal for weak ODR globals in the sense it
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
150 // doesn't change semantics, but we really don't want to perform it
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
151 // anyway; it's likely to pessimize code generation, and some tools
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
152 // (like the Darwin linker in cases involving CFString) don't expect it.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
153 if (GV->isWeakForLinker())
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
154 continue;
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 Constant *Init = GV->getInitializer();
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
157
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
158 // Check to see if the initializer is already known.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
159 PointerIntPair<Constant*, 1, bool> Pair(Init, hasKnownAlignment(GV));
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
160 GlobalVariable *&Slot = CMap[Pair];
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
161
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
162 // 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
163 // 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
164 // 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
165 if (!Slot || IsBetterCanonical(*GV, *Slot))
0
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
166 Slot = GV;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
167 }
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
168
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
169 // 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
170 // 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
171 // 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
172 // invalidating the Constant* pointers in CMap.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
173 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
174 GVI != E; ) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
175 GlobalVariable *GV = GVI++;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
176
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
177 // 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
178 if (!GV->isConstant() || !GV->hasDefinitiveInitializer() ||
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
179 GV->getType()->getAddressSpace() != 0 || GV->hasSection() ||
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
180 // Don't touch values marked with attribute(used).
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
181 UsedGlobals.count(GV))
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
182 continue;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
183
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
184 // We can only replace constant with local linkage.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
185 if (!GV->hasLocalLinkage())
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
186 continue;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
187
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
188 Constant *Init = GV->getInitializer();
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
189
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
190 // Check to see if the initializer is already known.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
191 PointerIntPair<Constant*, 1, bool> Pair(Init, hasKnownAlignment(GV));
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
192 GlobalVariable *Slot = CMap[Pair];
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 if (!Slot || Slot == GV)
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
195 continue;
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 if (!Slot->hasUnnamedAddr() && !GV->hasUnnamedAddr())
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
198 continue;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
199
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
200 if (!GV->hasUnnamedAddr())
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
201 Slot->setUnnamedAddr(false);
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
202
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
203 // 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
204 Replacements.push_back(std::make_pair(GV, Slot));
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
205 }
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
206
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
207 if (Replacements.empty())
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
208 return MadeChange;
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
209 CMap.clear();
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
210
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
211 // 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
212 // 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
213 // now.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
214 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
215 // Bump the alignment if necessary.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
216 if (Replacements[i].first->getAlignment() ||
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
217 Replacements[i].second->getAlignment()) {
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
218 Replacements[i].second->setAlignment(
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
219 std::max(getAlignment(Replacements[i].first),
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
220 getAlignment(Replacements[i].second)));
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
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
223 // Eliminate any uses of the dead global.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
224 Replacements[i].first->replaceAllUsesWith(Replacements[i].second);
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
225
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
226 // Delete the global value from the module.
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
227 assert(Replacements[i].first->hasLocalLinkage() &&
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
228 "Refusing to delete an externally visible global variable.");
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
229 Replacements[i].first->eraseFromParent();
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
230 }
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
231
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
232 NumMerged += Replacements.size();
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
233 Replacements.clear();
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
234 }
95c75e76d11b LLVM 3.4
Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
parents:
diff changeset
235 }