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 (isa<DerivedType>(C->getOperand(i)->getType()) &&
 147         OnlyUsedBy(C->getOperand(i), C))
 148       Operands.insert(cast<Constant>(C->getOperand(i)));
 149   if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
 150     if (!GV->hasLocalLinkage()) return;   // Don't delete non static globals.
 151     GV->eraseFromParent();
 152   }
 153   else if (!isa<Function>(C))
 154     if (isa<CompositeType>(C->getType()))
 155       C->destroyConstant();
 156
 157   // If the constant referenced anything, see if we can delete it as well.
 158   for (SmallPtrSet<Constant*, 4>::iterator OI = Operands.begin(),
 159          OE = Operands.end(); OI != OE; ++OI)
 160     RemoveDeadConstant(*OI);
 161 }
 162
 163 // Strip the symbol table of its names.
 164 //
 165 static void StripSymtab(ValueSymbolTable &ST, bool PreserveDbgInfo) {
 166   for (ValueSymbolTable::iterator VI = ST.begin(), VE = ST.end(); VI != VE; ) {
 167     Value *V = VI->getValue();
 168     ++VI;
 169     if (!isa<GlobalValue>(V) || cast<GlobalValue>(V)->hasLocalLinkage()) {
 170       if (!PreserveDbgInfo || !V->getName().startswith("llvm.dbg"))
 171         // Set name to "", removing from symbol table!
 172         V->setName("");
 173     }
 174   }
 175 }
 176
 177 // Strip any named types of their names.
 178 static void StripTypeNames(Module &M, bool PreserveDbgInfo) {
 179   std::vector<StructType*> StructTypes;
 180   M.findUsedStructTypes(StructTypes);
 181
 182   for (unsigned i = 0, e = StructTypes.size(); i != e; ++i) {
 183     StructType *STy = StructTypes[i];
 184     if (STy->isAnonymous() || STy->getName().empty()) continue;
 185
 186     if (PreserveDbgInfo && STy->getName().startswith("llvm.dbg"))
 187       continue;
 188
 189     STy->setName("");
 190   }
 191 }
 192
 193 /// Find values that are marked as llvm.used.
 194 static void findUsedValues(GlobalVariable *LLVMUsed,
 195                            SmallPtrSet<const GlobalValue*, 8> &UsedValues) {
 196   if (LLVMUsed == 0) return;
 197   UsedValues.insert(LLVMUsed);
 198
 199   ConstantArray *Inits = dyn_cast<ConstantArray>(LLVMUsed->getInitializer());
 200   if (Inits == 0) return;
 201
 202   for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i)
 203     if (GlobalValue *GV =
 204           dyn_cast<GlobalValue>(Inits->getOperand(i)->stripPointerCasts()))
 205       UsedValues.insert(GV);
 206 }
 207
 208 /// StripSymbolNames - Strip symbol names.
 209 static bool StripSymbolNames(Module &M, bool PreserveDbgInfo) {
 210
 211   SmallPtrSet<const GlobalValue*, 8> llvmUsedValues;
 212   findUsedValues(M.getGlobalVariable("llvm.used"), llvmUsedValues);
 213   findUsedValues(M.getGlobalVariable("llvm.compiler.used"), llvmUsedValues);
 214
 215   for (Module::global_iterator I = M.global_begin(), E = M.global_end();
 216        I != E; ++I) {
 217     if (I->hasLocalLinkage() && llvmUsedValues.count(I) == 0)
 218       if (!PreserveDbgInfo || !I->getName().startswith("llvm.dbg"))
 219         I->setName("");     // Internal symbols can't participate in linkage
 220   }
 221
 222   for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
 223     if (I->hasLocalLinkage() && llvmUsedValues.count(I) == 0)
 224       if (!PreserveDbgInfo || !I->getName().startswith("llvm.dbg"))
 225         I->setName("");     // Internal symbols can't participate in linkage
 226     StripSymtab(I->getValueSymbolTable(), PreserveDbgInfo);
 227   }
 228
 229   // Remove all names from types.
 230   StripTypeNames(M, PreserveDbgInfo);
 231
 232   return true;
 233 }
 234
 235 // StripDebugInfo - Strip debug info in the module if it exists.
 236 // To do this, we remove llvm.dbg.func.start, llvm.dbg.stoppoint, and
 237 // llvm.dbg.region.end calls, and any globals they point to if now dead.
 238 static bool StripDebugInfo(Module &M) {
 239
 240   bool Changed = false;
 241
 242   // Remove all of the calls to the debugger intrinsics, and remove them from
 243   // the module.
 244   if (Function *Declare = M.getFunction("llvm.dbg.declare")) {
 245     while (!Declare->use_empty()) {
 246       CallInst *CI = cast<CallInst>(Declare->use_back());
 247       CI->eraseFromParent();
 248     }
 249     Declare->eraseFromParent();
 250     Changed = true;
 251   }
 252
 253   if (Function *DbgVal = M.getFunction("llvm.dbg.value")) {
 254     while (!DbgVal->use_empty()) {
 255       CallInst *CI = cast<CallInst>(DbgVal->use_back());
 256       CI->eraseFromParent();
 257     }
 258     DbgVal->eraseFromParent();
 259     Changed = true;
 260   }
 261
 262   for (Module::named_metadata_iterator NMI = M.named_metadata_begin(),
 263          NME = M.named_metadata_end(); NMI != NME;) {
 264     NamedMDNode *NMD = NMI;
 265     ++NMI;
 266     if (NMD->getName().startswith("llvm.dbg.")) {
 267       NMD->eraseFromParent();
 268       Changed = true;
 269     }
 270   }
 271
 272   for (Module::iterator MI = M.begin(), ME = M.end(); MI != ME; ++MI)
 273     for (Function::iterator FI = MI->begin(), FE = MI->end(); FI != FE;
 274          ++FI)
 275       for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE;
 276            ++BI) {
 277         if (!BI->getDebugLoc().isUnknown()) {
 278           Changed = true;
 279           BI->setDebugLoc(DebugLoc());
 280         }
 281       }
 282
 283   return Changed;
 284 }
 285
 286 bool StripSymbols::runOnModule(Module &M) {
 287   bool Changed = false;
 288   Changed |= StripDebugInfo(M);
 289   if (!OnlyDebugInfo)
 290     Changed |= StripSymbolNames(M, false);
 291   return Changed;
 292 }
 293
 294 bool StripNonDebugSymbols::runOnModule(Module &M) {
 295   return StripSymbolNames(M, true);
 296 }
 297
 298 bool StripDebugDeclare::runOnModule(Module &M) {
 299
 300   Function *Declare = M.getFunction("llvm.dbg.declare");
 301   std::vector<Constant*> DeadConstants;
 302
 303   if (Declare) {
 304     while (!Declare->use_empty()) {
 305       CallInst *CI = cast<CallInst>(Declare->use_back());
 306       Value *Arg1 = CI->getArgOperand(0);
 307       Value *Arg2 = CI->getArgOperand(1);
 308       assert(CI->use_empty() && "llvm.dbg intrinsic should have void result");
 309       CI->eraseFromParent();
 310       if (Arg1->use_empty()) {
 311         if (Constant *C = dyn_cast<Constant>(Arg1))
 312           DeadConstants.push_back(C);
 313         else
 314           RecursivelyDeleteTriviallyDeadInstructions(Arg1);
 315       }
 316       if (Arg2->use_empty())
 317         if (Constant *C = dyn_cast<Constant>(Arg2))
 318           DeadConstants.push_back(C);
 319     }
 320     Declare->eraseFromParent();
 321   }
 322
 323   while (!DeadConstants.empty()) {
 324     Constant *C = DeadConstants.back();
 325     DeadConstants.pop_back();
 326     if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
 327       if (GV->hasLocalLinkage())
 328         RemoveDeadConstant(GV);
 329     } else
 330       RemoveDeadConstant(C);
 331   }
 332
 333   return true;
 334 }
 335
 336 /// getRealLinkageName - If special LLVM prefix that is used to inform the asm
 337 /// printer to not emit usual symbol prefix before the symbol name is used then
 338 /// return linkage name after skipping this special LLVM prefix.
 339 static StringRef getRealLinkageName(StringRef LinkageName) {
 340   char One = '\1';
 341   if (LinkageName.startswith(StringRef(&One, 1)))
 342     return LinkageName.substr(1);
 343   return LinkageName;
 344 }
 345
 346 bool StripDeadDebugInfo::runOnModule(Module &M) {
 347   bool Changed = false;
 348
 349   // Debugging infomration is encoded in llvm IR using metadata. This is designed
 350   // such a way that debug info for symbols preserved even if symbols are
 351   // optimized away by the optimizer. This special pass removes debug info for
 352   // such symbols.
 353
 354   // llvm.dbg.gv keeps track of debug info for global variables.
 355   if (NamedMDNode *NMD = M.getNamedMetadata("llvm.dbg.gv")) {
 356     SmallVector<MDNode *, 8> MDs;
 357     for (unsigned i = 0, e = NMD->getNumOperands(); i != e; ++i)
 358       if (DIGlobalVariable(NMD->getOperand(i)).Verify())
 359         MDs.push_back(NMD->getOperand(i));
 360       else
 361         Changed = true;
 362     NMD->eraseFromParent();
 363     NMD = NULL;
 364
 365     for (SmallVector<MDNode *, 8>::iterator I = MDs.begin(),
 366            E = MDs.end(); I != E; ++I) {
 367       GlobalVariable *GV = DIGlobalVariable(*I).getGlobal();
 368       if (GV && M.getGlobalVariable(GV->getName(), true)) {
 369         if (!NMD)
 370           NMD = M.getOrInsertNamedMetadata("llvm.dbg.gv");
 371         NMD->addOperand(*I);
 372       }
 373       else
 374         Changed = true;
 375     }
 376   }
 377
 378   // llvm.dbg.sp keeps track of debug info for subprograms.
 379   if (NamedMDNode *NMD = M.getNamedMetadata("llvm.dbg.sp")) {
 380     SmallVector<MDNode *, 8> MDs;
 381     for (unsigned i = 0, e = NMD->getNumOperands(); i != e; ++i)
 382       if (DISubprogram(NMD->getOperand(i)).Verify())
 383         MDs.push_back(NMD->getOperand(i));
 384       else
 385         Changed = true;
 386     NMD->eraseFromParent();
 387     NMD = NULL;
 388
 389     for (SmallVector<MDNode *, 8>::iterator I = MDs.begin(),
 390            E = MDs.end(); I != E; ++I) {
 391       bool FnIsLive = false;
 392       if (Function *F = DISubprogram(*I).getFunction())
 393         if (M.getFunction(F->getName()))
 394           FnIsLive = true;
 395       if (FnIsLive) {
 396           if (!NMD)
 397             NMD = M.getOrInsertNamedMetadata("llvm.dbg.sp");
 398           NMD->addOperand(*I);
 399       } else {
 400         // Remove llvm.dbg.lv.fnname named mdnode which may have been used
 401         // to hold debug info for dead function's local variables.
 402         StringRef FName = DISubprogram(*I).getLinkageName();
 403         if (FName.empty())
 404           FName = DISubprogram(*I).getName();
 405         if (NamedMDNode *LVNMD =
 406             M.getNamedMetadata(Twine("llvm.dbg.lv.",
 407                                      getRealLinkageName(FName))))
 408           LVNMD->eraseFromParent();
 409       }
 410     }
 411   }
 412
 413   return Changed;
 414 }