1 //===- StripSymbols.cpp - Strip symbols and debug info from a module ------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // The StripSymbols transformation implements code stripping. Specifically, it
13 // * names for virtual registers
14 // * symbols for internal globals and functions
15 // * debug information
17 // Note that this transformation makes code much less readable, so it should
18 // only be used in situations where the 'strip' utility would be used, such as
19 // reducing code size or making it harder to reverse engineer code.
21 //===----------------------------------------------------------------------===//
23 #include "llvm/Transforms/IPO.h"
24 #include "llvm/Constants.h"
25 #include "llvm/DerivedTypes.h"
26 #include "llvm/Instructions.h"
27 #include "llvm/Module.h"
28 #include "llvm/Pass.h"
29 #include "llvm/ValueSymbolTable.h"
30 #include "llvm/TypeSymbolTable.h"
31 #include "llvm/Support/Compiler.h"
32 #include "llvm/ADT/SmallPtrSet.h"
36 class VISIBILITY_HIDDEN StripSymbols : public ModulePass {
39 static char ID; // Pass identification, replacement for typeid
40 explicit StripSymbols(bool ODI = false)
41 : ModulePass((intptr_t)&ID), OnlyDebugInfo(ODI) {}
43 virtual bool runOnModule(Module &M);
45 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
50 char StripSymbols::ID = 0;
51 RegisterPass<StripSymbols> X("strip", "Strip all symbols from a module");
54 ModulePass *llvm::createStripSymbolsPass(bool OnlyDebugInfo) {
55 return new StripSymbols(OnlyDebugInfo);
58 static void RemoveDeadConstant(Constant *C) {
59 assert(C->use_empty() && "Constant is not dead!");
60 std::vector<Constant*> Operands;
61 for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i)
62 if (isa<DerivedType>(C->getOperand(i)->getType()) &&
63 C->getOperand(i)->hasOneUse())
64 Operands.push_back(C->getOperand(i));
65 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
66 if (!GV->hasInternalLinkage()) return; // Don't delete non static globals.
67 GV->eraseFromParent();
69 else if (!isa<Function>(C))
72 // If the constant referenced anything, see if we can delete it as well.
73 while (!Operands.empty()) {
74 RemoveDeadConstant(Operands.back());
79 // Strip the symbol table of its names.
81 static void StripSymtab(ValueSymbolTable &ST) {
82 for (ValueSymbolTable::iterator VI = ST.begin(), VE = ST.end(); VI != VE; ) {
83 Value *V = VI->getValue();
85 if (!isa<GlobalValue>(V) || cast<GlobalValue>(V)->hasInternalLinkage()) {
86 // Set name to "", removing from symbol table!
92 // Strip the symbol table of its names.
93 static void StripTypeSymtab(TypeSymbolTable &ST) {
94 for (TypeSymbolTable::iterator TI = ST.begin(), E = ST.end(); TI != E; )
100 bool StripSymbols::runOnModule(Module &M) {
101 // If we're not just stripping debug info, strip all symbols from the
102 // functions and the names from any internal globals.
103 if (!OnlyDebugInfo) {
104 SmallPtrSet<const GlobalValue*, 8> llvmUsedValues;
105 if (GlobalVariable *LLVMUsed = M.getGlobalVariable("llvm.used")) {
106 llvmUsedValues.insert(LLVMUsed);
107 // Collect values that are preserved as per explicit request.
108 // llvm.used is used to list these values.
109 if (ConstantArray *Inits =
110 dyn_cast<ConstantArray>(LLVMUsed->getInitializer())) {
111 for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i) {
112 if (GlobalValue *GV = dyn_cast<GlobalValue>(Inits->getOperand(i)))
113 llvmUsedValues.insert(GV);
114 else if (ConstantExpr *CE =
115 dyn_cast<ConstantExpr>(Inits->getOperand(i)))
116 if (CE->getOpcode() == Instruction::BitCast)
117 if (GlobalValue *GV = dyn_cast<GlobalValue>(CE->getOperand(0)))
118 llvmUsedValues.insert(GV);
123 for (Module::global_iterator I = M.global_begin(), E = M.global_end();
125 if (I->hasInternalLinkage() && llvmUsedValues.count(I) == 0)
126 I->setName(""); // Internal symbols can't participate in linkage
129 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
130 if (I->hasInternalLinkage() && llvmUsedValues.count(I) == 0)
131 I->setName(""); // Internal symbols can't participate in linkage
132 StripSymtab(I->getValueSymbolTable());
135 // Remove all names from types.
136 StripTypeSymtab(M.getTypeSymbolTable());
139 // Strip debug info in the module if it exists. To do this, we remove
140 // llvm.dbg.func.start, llvm.dbg.stoppoint, and llvm.dbg.region.end calls, and
141 // any globals they point to if now dead.
142 Function *FuncStart = M.getFunction("llvm.dbg.func.start");
143 Function *StopPoint = M.getFunction("llvm.dbg.stoppoint");
144 Function *RegionStart = M.getFunction("llvm.dbg.region.start");
145 Function *RegionEnd = M.getFunction("llvm.dbg.region.end");
146 Function *Declare = M.getFunction("llvm.dbg.declare");
147 if (!FuncStart && !StopPoint && !RegionStart && !RegionEnd && !Declare)
150 std::vector<GlobalVariable*> DeadGlobals;
152 // Remove all of the calls to the debugger intrinsics, and remove them from
155 while (!FuncStart->use_empty()) {
156 CallInst *CI = cast<CallInst>(FuncStart->use_back());
157 Value *Arg = CI->getOperand(1);
158 assert(CI->use_empty() && "llvm.dbg intrinsic should have void result");
159 CI->eraseFromParent();
160 if (Arg->use_empty())
161 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Arg))
162 DeadGlobals.push_back(GV);
164 FuncStart->eraseFromParent();
167 while (!StopPoint->use_empty()) {
168 CallInst *CI = cast<CallInst>(StopPoint->use_back());
169 Value *Arg = CI->getOperand(3);
170 assert(CI->use_empty() && "llvm.dbg intrinsic should have void result");
171 CI->eraseFromParent();
172 if (Arg->use_empty())
173 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Arg))
174 DeadGlobals.push_back(GV);
176 StopPoint->eraseFromParent();
179 while (!RegionStart->use_empty()) {
180 CallInst *CI = cast<CallInst>(RegionStart->use_back());
181 Value *Arg = CI->getOperand(1);
182 assert(CI->use_empty() && "llvm.dbg intrinsic should have void result");
183 CI->eraseFromParent();
184 if (Arg->use_empty())
185 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Arg))
186 DeadGlobals.push_back(GV);
188 RegionStart->eraseFromParent();
191 while (!RegionEnd->use_empty()) {
192 CallInst *CI = cast<CallInst>(RegionEnd->use_back());
193 Value *Arg = CI->getOperand(1);
194 assert(CI->use_empty() && "llvm.dbg intrinsic should have void result");
195 CI->eraseFromParent();
196 if (Arg->use_empty())
197 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Arg))
198 DeadGlobals.push_back(GV);
200 RegionEnd->eraseFromParent();
203 while (!Declare->use_empty()) {
204 CallInst *CI = cast<CallInst>(Declare->use_back());
205 Value *Arg = CI->getOperand(2);
206 assert(CI->use_empty() && "llvm.dbg intrinsic should have void result");
207 CI->eraseFromParent();
208 if (Arg->use_empty())
209 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Arg))
210 DeadGlobals.push_back(GV);
212 Declare->eraseFromParent();
215 // Finally, delete any internal globals that were only used by the debugger
217 while (!DeadGlobals.empty()) {
218 GlobalVariable *GV = DeadGlobals.back();
219 DeadGlobals.pop_back();
220 if (GV->hasInternalLinkage())
221 RemoveDeadConstant(GV);