1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
|
//===- ConstantMerge.cpp - Merge duplicate global constants ---------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the interface to a pass that merges duplicate global
// constants together into a single constant that is shared. This is useful
// because some passes (ie TraceValues) insert a lot of string constants into
// the program, regardless of whether or not an existing string is available.
//
// Algorithm: ConstantMerge is designed to build up a map of available constants
// and eliminate duplicates when it is initialized.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "constmerge"
#include "llvm/Transforms/IPO.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
STATISTIC(NumMerged, "Number of global constants merged");
namespace {
struct ConstantMerge : public ModulePass {
static char ID; // Pass identification, replacement for typeid
ConstantMerge() : ModulePass(ID) {
initializeConstantMergePass(*PassRegistry::getPassRegistry());
}
// run - For this pass, process all of the globals in the module,
// eliminating duplicate constants.
//
bool runOnModule(Module &M);
};
}
char ConstantMerge::ID = 0;
INITIALIZE_PASS(ConstantMerge, "constmerge",
"Merge Duplicate Global Constants", false, false)
ModulePass *llvm::createConstantMergePass() { return new ConstantMerge(); }
/// Find values that are marked as llvm.used.
static void FindUsedValues(GlobalVariable *LLVMUsed,
SmallPtrSet<const GlobalValue*, 8> &UsedValues) {
if (LLVMUsed == 0) return;
ConstantArray *Inits = dyn_cast<ConstantArray>(LLVMUsed->getInitializer());
if (Inits == 0) return;
for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i)
if (GlobalValue *GV =
dyn_cast<GlobalValue>(Inits->getOperand(i)->stripPointerCasts()))
UsedValues.insert(GV);
}
bool ConstantMerge::runOnModule(Module &M) {
// Find all the globals that are marked "used". These cannot be merged.
SmallPtrSet<const GlobalValue*, 8> UsedGlobals;
FindUsedValues(M.getGlobalVariable("llvm.used"), UsedGlobals);
FindUsedValues(M.getGlobalVariable("llvm.compiler.used"), UsedGlobals);
// Map unique constant/section pairs to globals. We don't want to merge
// globals in different sections.
DenseMap<Constant*, GlobalVariable*> CMap;
// Replacements - This vector contains a list of replacements to perform.
SmallVector<std::pair<GlobalVariable*, GlobalVariable*>, 32> Replacements;
bool MadeChange = false;
// Iterate constant merging while we are still making progress. Merging two
// constants together may allow us to merge other constants together if the
// second level constants have initializers which point to the globals that
// were just merged.
while (1) {
// First pass: identify all globals that can be merged together, filling in
// the Replacements vector. We cannot do the replacement in this pass
// because doing so may cause initializers of other globals to be rewritten,
// invalidating the Constant* pointers in CMap.
//
for (Module::global_iterator GVI = M.global_begin(), E = M.global_end();
GVI != E; ) {
GlobalVariable *GV = GVI++;
// If this GV is dead, remove it.
GV->removeDeadConstantUsers();
if (GV->use_empty() && GV->hasLocalLinkage()) {
GV->eraseFromParent();
continue;
}
// Only process constants with initializers in the default addres space.
if (!GV->isConstant() ||!GV->hasDefinitiveInitializer() ||
GV->getType()->getAddressSpace() != 0 || !GV->getSection().empty() ||
// Don't touch values marked with attribute(used).
UsedGlobals.count(GV))
continue;
Constant *Init = GV->getInitializer();
// Check to see if the initializer is already known.
GlobalVariable *&Slot = CMap[Init];
if (Slot == 0) { // Nope, add it to the map.
Slot = GV;
} else if (GV->hasLocalLinkage()) { // Yup, this is a duplicate!
// Make all uses of the duplicate constant use the canonical version.
Replacements.push_back(std::make_pair(GV, Slot));
}
}
if (Replacements.empty())
return MadeChange;
CMap.clear();
// Now that we have figured out which replacements must be made, do them all
// now. This avoid invalidating the pointers in CMap, which are unneeded
// now.
for (unsigned i = 0, e = Replacements.size(); i != e; ++i) {
// Eliminate any uses of the dead global.
Replacements[i].first->replaceAllUsesWith(Replacements[i].second);
// Delete the global value from the module.
Replacements[i].first->eraseFromParent();
}
NumMerged += Replacements.size();
Replacements.clear();
}
}
|
