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
|
//===- DCE.cpp - Code to perform dead code elimination --------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements dead inst elimination and dead code elimination.
//
// Dead Inst Elimination performs a single pass over the function removing
// instructions that are obviously dead. Dead Code Elimination is similar, but
// it rechecks instructions that were used by removed instructions to see if
// they are newly dead.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "dce"
#include "llvm/Transforms/Scalar.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/IR/Instruction.h"
#include "llvm/Pass.h"
#include "llvm/Support/InstIterator.h"
#include "llvm/Target/TargetLibraryInfo.h"
#include "llvm/Transforms/Utils/Local.h"
using namespace llvm;
STATISTIC(DIEEliminated, "Number of insts removed by DIE pass");
STATISTIC(DCEEliminated, "Number of insts removed");
namespace {
//===--------------------------------------------------------------------===//
// DeadInstElimination pass implementation
//
struct DeadInstElimination : public BasicBlockPass {
static char ID; // Pass identification, replacement for typeid
DeadInstElimination() : BasicBlockPass(ID) {
initializeDeadInstEliminationPass(*PassRegistry::getPassRegistry());
}
virtual bool runOnBasicBlock(BasicBlock &BB) {
TargetLibraryInfo *TLI = getAnalysisIfAvailable<TargetLibraryInfo>();
bool Changed = false;
for (BasicBlock::iterator DI = BB.begin(); DI != BB.end(); ) {
Instruction *Inst = DI++;
if (isInstructionTriviallyDead(Inst, TLI)) {
Inst->eraseFromParent();
Changed = true;
++DIEEliminated;
}
}
return Changed;
}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
}
};
}
char DeadInstElimination::ID = 0;
INITIALIZE_PASS(DeadInstElimination, "die",
"Dead Instruction Elimination", false, false)
Pass *llvm::createDeadInstEliminationPass() {
return new DeadInstElimination();
}
namespace {
//===--------------------------------------------------------------------===//
// DeadCodeElimination pass implementation
//
struct DCE : public FunctionPass {
static char ID; // Pass identification, replacement for typeid
DCE() : FunctionPass(ID) {
initializeDCEPass(*PassRegistry::getPassRegistry());
}
virtual bool runOnFunction(Function &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
}
};
}
char DCE::ID = 0;
INITIALIZE_PASS(DCE, "dce", "Dead Code Elimination", false, false)
bool DCE::runOnFunction(Function &F) {
TargetLibraryInfo *TLI = getAnalysisIfAvailable<TargetLibraryInfo>();
// Start out with all of the instructions in the worklist...
std::vector<Instruction*> WorkList;
for (inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i)
WorkList.push_back(&*i);
// Loop over the worklist finding instructions that are dead. If they are
// dead make them drop all of their uses, making other instructions
// potentially dead, and work until the worklist is empty.
//
bool MadeChange = false;
while (!WorkList.empty()) {
Instruction *I = WorkList.back();
WorkList.pop_back();
if (isInstructionTriviallyDead(I, TLI)) { // If the instruction is dead.
// Loop over all of the values that the instruction uses, if there are
// instructions being used, add them to the worklist, because they might
// go dead after this one is removed.
//
for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI)
if (Instruction *Used = dyn_cast<Instruction>(*OI))
WorkList.push_back(Used);
// Remove the instruction.
I->eraseFromParent();
// Remove the instruction from the worklist if it still exists in it.
WorkList.erase(std::remove(WorkList.begin(), WorkList.end(), I),
WorkList.end());
MadeChange = true;
++DCEEliminated;
}
}
return MadeChange;
}
FunctionPass *llvm::createDeadCodeEliminationPass() {
return new DCE();
}
|
