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