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/ADT/DenseMap.h"
25 #include "llvm/ADT/SmallPtrSet.h"
26 #include "llvm/IR/Constants.h"
27 #include "llvm/IR/DebugInfo.h"
28 #include "llvm/IR/DerivedTypes.h"
29 #include "llvm/IR/Instructions.h"
30 #include "llvm/IR/Module.h"
31 #include "llvm/IR/TypeFinder.h"
32 #include "llvm/IR/ValueSymbolTable.h"
33 #include "llvm/Pass.h"
34 #include "llvm/Transforms/Utils/Local.h"
38 class StripSymbols : public ModulePass {
41 static char ID; // Pass identification, replacement for typeid
42 explicit StripSymbols(bool ODI = false)
43 : ModulePass(ID), OnlyDebugInfo(ODI) {
44 initializeStripSymbolsPass(*PassRegistry::getPassRegistry());
47 bool runOnModule(Module &M) override;
49 void getAnalysisUsage(AnalysisUsage &AU) const override {
54 class StripNonDebugSymbols : public ModulePass {
56 static char ID; // Pass identification, replacement for typeid
57 explicit StripNonDebugSymbols()
59 initializeStripNonDebugSymbolsPass(*PassRegistry::getPassRegistry());
62 bool runOnModule(Module &M) override;
64 void getAnalysisUsage(AnalysisUsage &AU) const override {
69 class StripDebugDeclare : public ModulePass {
71 static char ID; // Pass identification, replacement for typeid
72 explicit StripDebugDeclare()
74 initializeStripDebugDeclarePass(*PassRegistry::getPassRegistry());
77 bool runOnModule(Module &M) override;
79 void getAnalysisUsage(AnalysisUsage &AU) const override {
84 class StripDeadDebugInfo : public ModulePass {
86 static char ID; // Pass identification, replacement for typeid
87 explicit StripDeadDebugInfo()
89 initializeStripDeadDebugInfoPass(*PassRegistry::getPassRegistry());
92 bool runOnModule(Module &M) override;
94 void getAnalysisUsage(AnalysisUsage &AU) const override {
100 char StripSymbols::ID = 0;
101 INITIALIZE_PASS(StripSymbols, "strip",
102 "Strip all symbols from a module", false, false)
104 ModulePass *llvm::createStripSymbolsPass(bool OnlyDebugInfo) {
105 return new StripSymbols(OnlyDebugInfo);
108 char StripNonDebugSymbols::ID = 0;
109 INITIALIZE_PASS(StripNonDebugSymbols, "strip-nondebug",
110 "Strip all symbols, except dbg symbols, from a module",
113 ModulePass *llvm::createStripNonDebugSymbolsPass() {
114 return new StripNonDebugSymbols();
117 char StripDebugDeclare::ID = 0;
118 INITIALIZE_PASS(StripDebugDeclare, "strip-debug-declare",
119 "Strip all llvm.dbg.declare intrinsics", false, false)
121 ModulePass *llvm::createStripDebugDeclarePass() {
122 return new StripDebugDeclare();
125 char StripDeadDebugInfo::ID = 0;
126 INITIALIZE_PASS(StripDeadDebugInfo, "strip-dead-debug-info",
127 "Strip debug info for unused symbols", false, false)
129 ModulePass *llvm::createStripDeadDebugInfoPass() {
130 return new StripDeadDebugInfo();
133 /// OnlyUsedBy - Return true if V is only used by Usr.
134 static bool OnlyUsedBy(Value *V, Value *Usr) {
135 for (User *U : V->users())
142 static void RemoveDeadConstant(Constant *C) {
143 assert(C->use_empty() && "Constant is not dead!");
144 SmallPtrSet<Constant*, 4> Operands;
145 for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i)
146 if (OnlyUsedBy(C->getOperand(i), C))
147 Operands.insert(cast<Constant>(C->getOperand(i)));
148 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
149 if (!GV->hasLocalLinkage()) return; // Don't delete non-static globals.
150 GV->eraseFromParent();
152 else if (!isa<Function>(C))
153 if (isa<CompositeType>(C->getType()))
154 C->destroyConstant();
156 // If the constant referenced anything, see if we can delete it as well.
157 for (Constant *O : Operands)
158 RemoveDeadConstant(O);
161 // Strip the symbol table of its names.
163 static void StripSymtab(ValueSymbolTable &ST, bool PreserveDbgInfo) {
164 for (ValueSymbolTable::iterator VI = ST.begin(), VE = ST.end(); VI != VE; ) {
165 Value *V = VI->getValue();
167 if (!isa<GlobalValue>(V) || cast<GlobalValue>(V)->hasLocalLinkage()) {
168 if (!PreserveDbgInfo || !V->getName().startswith("llvm.dbg"))
169 // Set name to "", removing from symbol table!
175 // Strip any named types of their names.
176 static void StripTypeNames(Module &M, bool PreserveDbgInfo) {
177 TypeFinder StructTypes;
178 StructTypes.run(M, false);
180 for (unsigned i = 0, e = StructTypes.size(); i != e; ++i) {
181 StructType *STy = StructTypes[i];
182 if (STy->isLiteral() || STy->getName().empty()) continue;
184 if (PreserveDbgInfo && STy->getName().startswith("llvm.dbg"))
191 /// Find values that are marked as llvm.used.
192 static void findUsedValues(GlobalVariable *LLVMUsed,
193 SmallPtrSetImpl<const GlobalValue*> &UsedValues) {
194 if (!LLVMUsed) return;
195 UsedValues.insert(LLVMUsed);
197 ConstantArray *Inits = cast<ConstantArray>(LLVMUsed->getInitializer());
199 for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i)
200 if (GlobalValue *GV =
201 dyn_cast<GlobalValue>(Inits->getOperand(i)->stripPointerCasts()))
202 UsedValues.insert(GV);
205 /// StripSymbolNames - Strip symbol names.
206 static bool StripSymbolNames(Module &M, bool PreserveDbgInfo) {
208 SmallPtrSet<const GlobalValue*, 8> llvmUsedValues;
209 findUsedValues(M.getGlobalVariable("llvm.used"), llvmUsedValues);
210 findUsedValues(M.getGlobalVariable("llvm.compiler.used"), llvmUsedValues);
212 for (Module::global_iterator I = M.global_begin(), E = M.global_end();
214 if (I->hasLocalLinkage() && llvmUsedValues.count(I) == 0)
215 if (!PreserveDbgInfo || !I->getName().startswith("llvm.dbg"))
216 I->setName(""); // Internal symbols can't participate in linkage
219 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
220 if (I->hasLocalLinkage() && llvmUsedValues.count(I) == 0)
221 if (!PreserveDbgInfo || !I->getName().startswith("llvm.dbg"))
222 I->setName(""); // Internal symbols can't participate in linkage
223 StripSymtab(I->getValueSymbolTable(), PreserveDbgInfo);
226 // Remove all names from types.
227 StripTypeNames(M, PreserveDbgInfo);
232 bool StripSymbols::runOnModule(Module &M) {
233 bool Changed = false;
234 Changed |= StripDebugInfo(M);
236 Changed |= StripSymbolNames(M, false);
240 bool StripNonDebugSymbols::runOnModule(Module &M) {
241 return StripSymbolNames(M, true);
244 bool StripDebugDeclare::runOnModule(Module &M) {
246 Function *Declare = M.getFunction("llvm.dbg.declare");
247 std::vector<Constant*> DeadConstants;
250 while (!Declare->use_empty()) {
251 CallInst *CI = cast<CallInst>(Declare->user_back());
252 Value *Arg1 = CI->getArgOperand(0);
253 Value *Arg2 = CI->getArgOperand(1);
254 assert(CI->use_empty() && "llvm.dbg intrinsic should have void result");
255 CI->eraseFromParent();
256 if (Arg1->use_empty()) {
257 if (Constant *C = dyn_cast<Constant>(Arg1))
258 DeadConstants.push_back(C);
260 RecursivelyDeleteTriviallyDeadInstructions(Arg1);
262 if (Arg2->use_empty())
263 if (Constant *C = dyn_cast<Constant>(Arg2))
264 DeadConstants.push_back(C);
266 Declare->eraseFromParent();
269 while (!DeadConstants.empty()) {
270 Constant *C = DeadConstants.back();
271 DeadConstants.pop_back();
272 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
273 if (GV->hasLocalLinkage())
274 RemoveDeadConstant(GV);
276 RemoveDeadConstant(C);
282 /// Remove any debug info for global variables/functions in the given module for
283 /// which said global variable/function no longer exists (i.e. is null).
285 /// Debugging information is encoded in llvm IR using metadata. This is designed
286 /// such a way that debug info for symbols preserved even if symbols are
287 /// optimized away by the optimizer. This special pass removes debug info for
289 bool StripDeadDebugInfo::runOnModule(Module &M) {
290 bool Changed = false;
292 LLVMContext &C = M.getContext();
294 // Find all debug info in F. This is actually overkill in terms of what we
295 // want to do, but we want to try and be as resilient as possible in the face
296 // of potential debug info changes by using the formal interfaces given to us
297 // as much as possible.
301 // For each compile unit, find the live set of global variables/functions and
302 // replace the current list of potentially dead global variables/functions
303 // with the live list.
304 SmallVector<Metadata *, 64> LiveGlobalVariables;
305 SmallVector<Metadata *, 64> LiveSubprograms;
306 DenseSet<const MDNode *> VisitedSet;
308 for (DICompileUnit *DIC : F.compile_units()) {
309 // Create our live subprogram list.
310 bool SubprogramChange = false;
311 for (DISubprogram *DISP : DIC->getSubprograms()) {
312 // Make sure we visit each subprogram only once.
313 if (!VisitedSet.insert(DISP).second)
316 // If the function referenced by DISP is not null, the function is live.
317 if (DISP->getFunction())
318 LiveSubprograms.push_back(DISP);
320 SubprogramChange = true;
323 // Create our live global variable list.
324 bool GlobalVariableChange = false;
325 for (DIGlobalVariable *DIG : DIC->getGlobalVariables()) {
326 // Make sure we only visit each global variable only once.
327 if (!VisitedSet.insert(DIG).second)
330 // If the global variable referenced by DIG is not null, the global
332 if (DIG->getVariable())
333 LiveGlobalVariables.push_back(DIG);
335 GlobalVariableChange = true;
338 // If we found dead subprograms or global variables, replace the current
339 // subprogram list/global variable list with our new live subprogram/global
341 if (SubprogramChange) {
342 DIC->replaceSubprograms(MDTuple::get(C, LiveSubprograms));
346 if (GlobalVariableChange) {
347 DIC->replaceGlobalVariables(MDTuple::get(C, LiveGlobalVariables));
351 // Reset lists for the next iteration.
352 LiveSubprograms.clear();
353 LiveGlobalVariables.clear();