lib/Transforms/IPO/StripSymbols.cpp

   1 //===- StripSymbols.cpp - Strip symbols and debug info from a module ------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // The StripSymbols transformation implements code stripping. Specifically, it
  11 // can delete:
  12 //
  13 //   * names for virtual registers
  14 //   * symbols for internal globals and functions
  15 //   * debug information
  16 //
  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.
  20 //
  21 //===----------------------------------------------------------------------===//
  22
  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/Analysis/DebugInfo.h"
  30 #include "llvm/ValueSymbolTable.h"
  31 #include "llvm/Transforms/Utils/Local.h"
  32 #include "llvm/ADT/DenseMap.h"
  33 #include "llvm/ADT/SmallPtrSet.h"
  34 using namespace llvm;
  35
  36 namespace {
  37   class StripSymbols : public ModulePass {
  38     bool OnlyDebugInfo;
  39   public:
  40     static char ID; // Pass identification, replacement for typeid
  41     explicit StripSymbols(bool ODI = false)
  42       : ModulePass(ID), OnlyDebugInfo(ODI) {
  43         initializeStripSymbolsPass(*PassRegistry::getPassRegistry());
  44       }
  45
  46     virtual bool runOnModule(Module &M);
  47
  48     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  49       AU.setPreservesAll();
  50     }
  51   };
  52
  53   class StripNonDebugSymbols : public ModulePass {
  54   public:
  55     static char ID; // Pass identification, replacement for typeid
  56     explicit StripNonDebugSymbols()
  57       : ModulePass(ID) {
  58         initializeStripNonDebugSymbolsPass(*PassRegistry::getPassRegistry());
  59       }
  60
  61     virtual bool runOnModule(Module &M);
  62
  63     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  64       AU.setPreservesAll();
  65     }
  66   };
  67
  68   class StripDebugDeclare : public ModulePass {
  69   public:
  70     static char ID; // Pass identification, replacement for typeid
  71     explicit StripDebugDeclare()
  72       : ModulePass(ID) {
  73         initializeStripDebugDeclarePass(*PassRegistry::getPassRegistry());
  74       }
  75
  76     virtual bool runOnModule(Module &M);
  77
  78     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  79       AU.setPreservesAll();
  80     }
  81   };
  82
  83   class StripDeadDebugInfo : public ModulePass {
  84   public:
  85     static char ID; // Pass identification, replacement for typeid
  86     explicit StripDeadDebugInfo()
  87       : ModulePass(ID) {
  88         initializeStripDeadDebugInfoPass(*PassRegistry::getPassRegistry());
  89       }
  90
  91     virtual bool runOnModule(Module &M);
  92
  93     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  94       AU.setPreservesAll();
  95     }
  96   };
  97 }
  98
  99 char StripSymbols::ID = 0;
 100 INITIALIZE_PASS(StripSymbols, "strip",
 101                 "Strip all symbols from a module", false, false)
 102
 103 ModulePass *llvm::createStripSymbolsPass(bool OnlyDebugInfo) {
 104   return new StripSymbols(OnlyDebugInfo);
 105 }
 106
 107 char StripNonDebugSymbols::ID = 0;
 108 INITIALIZE_PASS(StripNonDebugSymbols, "strip-nondebug",
 109                 "Strip all symbols, except dbg symbols, from a module",
 110                 false, false)
 111
 112 ModulePass *llvm::createStripNonDebugSymbolsPass() {
 113   return new StripNonDebugSymbols();
 114 }
 115
 116 char StripDebugDeclare::ID = 0;
 117 INITIALIZE_PASS(StripDebugDeclare, "strip-debug-declare",
 118                 "Strip all llvm.dbg.declare intrinsics", false, false)
 119
 120 ModulePass *llvm::createStripDebugDeclarePass() {
 121   return new StripDebugDeclare();
 122 }
 123
 124 char StripDeadDebugInfo::ID = 0;
 125 INITIALIZE_PASS(StripDeadDebugInfo, "strip-dead-debug-info",
 126                 "Strip debug info for unused symbols", false, false)
 127
 128 ModulePass *llvm::createStripDeadDebugInfoPass() {
 129   return new StripDeadDebugInfo();
 130 }
 131
 132 /// OnlyUsedBy - Return true if V is only used by Usr.
 133 static bool OnlyUsedBy(Value *V, Value *Usr) {
 134   for(Value::use_iterator I = V->use_begin(), E = V->use_end(); I != E; ++I) {
 135     User *U = *I;
 136     if (U != Usr)
 137       return false;
 138   }
 139   return true;
 140 }
 141
 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();
 151   }
 152   else if (!isa<Function>(C))
 153     if (isa<CompositeType>(C->getType()))
 154       C->destroyConstant();
 155
 156   // If the constant referenced anything, see if we can delete it as well.
 157   for (SmallPtrSet<Constant*, 4>::iterator OI = Operands.begin(),
 158          OE = Operands.end(); OI != OE; ++OI)
 159     RemoveDeadConstant(*OI);
 160 }
 161
 162 // Strip the symbol table of its names.
 163 //
 164 static void StripSymtab(ValueSymbolTable &ST, bool PreserveDbgInfo) {
 165   for (ValueSymbolTable::iterator VI = ST.begin(), VE = ST.end(); VI != VE; ) {
 166     Value *V = VI->getValue();
 167     ++VI;
 168     if (!isa<GlobalValue>(V) || cast<GlobalValue>(V)->hasLocalLinkage()) {
 169       if (!PreserveDbgInfo || !V->getName().startswith("llvm.dbg"))
 170         // Set name to "", removing from symbol table!
 171         V->setName("");
 172     }
 173   }
 174 }
 175
 176 // Strip any named types of their names.
 177 static void StripTypeNames(Module &M, bool PreserveDbgInfo) {
 178   std::vector<StructType*> StructTypes;
 179   M.findUsedStructTypes(StructTypes);
 180
 181   for (unsigned i = 0, e = StructTypes.size(); i != e; ++i) {
 182     StructType *STy = StructTypes[i];
 183     if (STy->isAnonymous() || STy->getName().empty()) continue;
 184
 185     if (PreserveDbgInfo && STy->getName().startswith("llvm.dbg"))
 186       continue;
 187
 188     STy->setName("");
 189   }
 190 }
 191
 192 /// Find values that are marked as llvm.used.
 193 static void findUsedValues(GlobalVariable *LLVMUsed,
 194                            SmallPtrSet<const GlobalValue*, 8> &UsedValues) {
 195   if (LLVMUsed == 0) return;
 196   UsedValues.insert(LLVMUsed);
 197
 198   ConstantArray *Inits = dyn_cast<ConstantArray>(LLVMUsed->getInitializer());
 199   if (Inits == 0) return;
 200
 201   for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i)
 202     if (GlobalValue *GV =
 203           dyn_cast<GlobalValue>(Inits->getOperand(i)->stripPointerCasts()))
 204       UsedValues.insert(GV);
 205 }
 206
 207 /// StripSymbolNames - Strip symbol names.
 208 static bool StripSymbolNames(Module &M, bool PreserveDbgInfo) {
 209
 210   SmallPtrSet<const GlobalValue*, 8> llvmUsedValues;
 211   findUsedValues(M.getGlobalVariable("llvm.used"), llvmUsedValues);
 212   findUsedValues(M.getGlobalVariable("llvm.compiler.used"), llvmUsedValues);
 213
 214   for (Module::global_iterator I = M.global_begin(), E = M.global_end();
 215        I != E; ++I) {
 216     if (I->hasLocalLinkage() && llvmUsedValues.count(I) == 0)
 217       if (!PreserveDbgInfo || !I->getName().startswith("llvm.dbg"))
 218         I->setName("");     // Internal symbols can't participate in linkage
 219   }
 220
 221   for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
 222     if (I->hasLocalLinkage() && llvmUsedValues.count(I) == 0)
 223       if (!PreserveDbgInfo || !I->getName().startswith("llvm.dbg"))
 224         I->setName("");     // Internal symbols can't participate in linkage
 225     StripSymtab(I->getValueSymbolTable(), PreserveDbgInfo);
 226   }
 227
 228   // Remove all names from types.
 229   StripTypeNames(M, PreserveDbgInfo);
 230
 231   return true;
 232 }
 233
 234 // StripDebugInfo - Strip debug info in the module if it exists.
 235 // To do this, we remove llvm.dbg.func.start, llvm.dbg.stoppoint, and
 236 // llvm.dbg.region.end calls, and any globals they point to if now dead.
 237 static bool StripDebugInfo(Module &M) {
 238
 239   bool Changed = false;
 240
 241   // Remove all of the calls to the debugger intrinsics, and remove them from
 242   // the module.
 243   if (Function *Declare = M.getFunction("llvm.dbg.declare")) {
 244     while (!Declare->use_empty()) {
 245       CallInst *CI = cast<CallInst>(Declare->use_back());
 246       CI->eraseFromParent();
 247     }
 248     Declare->eraseFromParent();
 249     Changed = true;
 250   }
 251
 252   if (Function *DbgVal = M.getFunction("llvm.dbg.value")) {
 253     while (!DbgVal->use_empty()) {
 254       CallInst *CI = cast<CallInst>(DbgVal->use_back());
 255       CI->eraseFromParent();
 256     }
 257     DbgVal->eraseFromParent();
 258     Changed = true;
 259   }
 260
 261   for (Module::named_metadata_iterator NMI = M.named_metadata_begin(),
 262          NME = M.named_metadata_end(); NMI != NME;) {
 263     NamedMDNode *NMD = NMI;
 264     ++NMI;
 265     if (NMD->getName().startswith("llvm.dbg.")) {
 266       NMD->eraseFromParent();
 267       Changed = true;
 268     }
 269   }
 270
 271   for (Module::iterator MI = M.begin(), ME = M.end(); MI != ME; ++MI)
 272     for (Function::iterator FI = MI->begin(), FE = MI->end(); FI != FE;
 273          ++FI)
 274       for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE;
 275            ++BI) {
 276         if (!BI->getDebugLoc().isUnknown()) {
 277           Changed = true;
 278           BI->setDebugLoc(DebugLoc());
 279         }
 280       }
 281
 282   return Changed;
 283 }
 284
 285 bool StripSymbols::runOnModule(Module &M) {
 286   bool Changed = false;
 287   Changed |= StripDebugInfo(M);
 288   if (!OnlyDebugInfo)
 289     Changed |= StripSymbolNames(M, false);
 290   return Changed;
 291 }
 292
 293 bool StripNonDebugSymbols::runOnModule(Module &M) {
 294   return StripSymbolNames(M, true);
 295 }
 296
 297 bool StripDebugDeclare::runOnModule(Module &M) {
 298
 299   Function *Declare = M.getFunction("llvm.dbg.declare");
 300   std::vector<Constant*> DeadConstants;
 301
 302   if (Declare) {
 303     while (!Declare->use_empty()) {
 304       CallInst *CI = cast<CallInst>(Declare->use_back());
 305       Value *Arg1 = CI->getArgOperand(0);
 306       Value *Arg2 = CI->getArgOperand(1);
 307       assert(CI->use_empty() && "llvm.dbg intrinsic should have void result");
 308       CI->eraseFromParent();
 309       if (Arg1->use_empty()) {
 310         if (Constant *C = dyn_cast<Constant>(Arg1))
 311           DeadConstants.push_back(C);
 312         else
 313           RecursivelyDeleteTriviallyDeadInstructions(Arg1);
 314       }
 315       if (Arg2->use_empty())
 316         if (Constant *C = dyn_cast<Constant>(Arg2))
 317           DeadConstants.push_back(C);
 318     }
 319     Declare->eraseFromParent();
 320   }
 321
 322   while (!DeadConstants.empty()) {
 323     Constant *C = DeadConstants.back();
 324     DeadConstants.pop_back();
 325     if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
 326       if (GV->hasLocalLinkage())
 327         RemoveDeadConstant(GV);
 328     } else
 329       RemoveDeadConstant(C);
 330   }
 331
 332   return true;
 333 }
 334
 335 /// getRealLinkageName - If special LLVM prefix that is used to inform the asm
 336 /// printer to not emit usual symbol prefix before the symbol name is used then
 337 /// return linkage name after skipping this special LLVM prefix.
 338 static StringRef getRealLinkageName(StringRef LinkageName) {
 339   char One = '\1';
 340   if (LinkageName.startswith(StringRef(&One, 1)))
 341     return LinkageName.substr(1);
 342   return LinkageName;
 343 }
 344
 345 bool StripDeadDebugInfo::runOnModule(Module &M) {
 346   bool Changed = false;
 347
 348   // Debugging infomration is encoded in llvm IR using metadata. This is designed
 349   // such a way that debug info for symbols preserved even if symbols are
 350   // optimized away by the optimizer. This special pass removes debug info for
 351   // such symbols.
 352
 353   // llvm.dbg.gv keeps track of debug info for global variables.
 354   if (NamedMDNode *NMD = M.getNamedMetadata("llvm.dbg.gv")) {
 355     SmallVector<MDNode *, 8> MDs;
 356     for (unsigned i = 0, e = NMD->getNumOperands(); i != e; ++i)
 357       if (DIGlobalVariable(NMD->getOperand(i)).Verify())
 358         MDs.push_back(NMD->getOperand(i));
 359       else
 360         Changed = true;
 361     NMD->eraseFromParent();
 362     NMD = NULL;
 363
 364     for (SmallVector<MDNode *, 8>::iterator I = MDs.begin(),
 365            E = MDs.end(); I != E; ++I) {
 366       GlobalVariable *GV = DIGlobalVariable(*I).getGlobal();
 367       if (GV && M.getGlobalVariable(GV->getName(), true)) {
 368         if (!NMD)
 369           NMD = M.getOrInsertNamedMetadata("llvm.dbg.gv");
 370         NMD->addOperand(*I);
 371       }
 372       else
 373         Changed = true;
 374     }
 375   }
 376
 377   // llvm.dbg.sp keeps track of debug info for subprograms.
 378   if (NamedMDNode *NMD = M.getNamedMetadata("llvm.dbg.sp")) {
 379     SmallVector<MDNode *, 8> MDs;
 380     for (unsigned i = 0, e = NMD->getNumOperands(); i != e; ++i)
 381       if (DISubprogram(NMD->getOperand(i)).Verify())
 382         MDs.push_back(NMD->getOperand(i));
 383       else
 384         Changed = true;
 385     NMD->eraseFromParent();
 386     NMD = NULL;
 387
 388     for (SmallVector<MDNode *, 8>::iterator I = MDs.begin(),
 389            E = MDs.end(); I != E; ++I) {
 390       bool FnIsLive = false;
 391       if (Function *F = DISubprogram(*I).getFunction())
 392         if (M.getFunction(F->getName()))
 393           FnIsLive = true;
 394       if (FnIsLive) {
 395           if (!NMD)
 396             NMD = M.getOrInsertNamedMetadata("llvm.dbg.sp");
 397           NMD->addOperand(*I);
 398       } else {
 399         // Remove llvm.dbg.lv.fnname named mdnode which may have been used
 400         // to hold debug info for dead function's local variables.
 401         StringRef FName = DISubprogram(*I).getLinkageName();
 402         if (FName.empty())
 403           FName = DISubprogram(*I).getName();
 404         if (NamedMDNode *LVNMD =
 405             M.getNamedMetadata(Twine("llvm.dbg.lv.",
 406                                      getRealLinkageName(FName))))
 407           LVNMD->eraseFromParent();
 408       }
 409     }
 410   }
 411
 412   return Changed;
 413 }