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/LLVMContext.h"
  28 #include "llvm/Module.h"
  29 #include "llvm/Pass.h"
  30 #include "llvm/Analysis/DebugInfo.h"
  31 #include "llvm/ValueSymbolTable.h"
  32 #include "llvm/TypeSymbolTable.h"
  33 #include "llvm/Transforms/Utils/Local.h"
  34 #include "llvm/ADT/SmallPtrSet.h"
  35 using namespace llvm;
  36
  37 namespace {
  38   class StripSymbols : public ModulePass {
  39     bool OnlyDebugInfo;
  40   public:
  41     static char ID; // Pass identification, replacement for typeid
  42     explicit StripSymbols(bool ODI = false)
  43       : ModulePass(&ID), OnlyDebugInfo(ODI) {}
  44
  45     virtual bool runOnModule(Module &M);
  46
  47     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  48       AU.setPreservesAll();
  49     }
  50   };
  51
  52   class StripNonDebugSymbols : public ModulePass {
  53   public:
  54     static char ID; // Pass identification, replacement for typeid
  55     explicit StripNonDebugSymbols()
  56       : ModulePass(&ID) {}
  57
  58     virtual bool runOnModule(Module &M);
  59
  60     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  61       AU.setPreservesAll();
  62     }
  63   };
  64
  65   class StripDebugDeclare : public ModulePass {
  66   public:
  67     static char ID; // Pass identification, replacement for typeid
  68     explicit StripDebugDeclare()
  69       : ModulePass(&ID) {}
  70
  71     virtual bool runOnModule(Module &M);
  72
  73     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  74       AU.setPreservesAll();
  75     }
  76   };
  77 }
  78
  79 char StripSymbols::ID = 0;
  80 static RegisterPass<StripSymbols>
  81 X("strip", "Strip all symbols from a module");
  82
  83 ModulePass *llvm::createStripSymbolsPass(bool OnlyDebugInfo) {
  84   return new StripSymbols(OnlyDebugInfo);
  85 }
  86
  87 char StripNonDebugSymbols::ID = 0;
  88 static RegisterPass<StripNonDebugSymbols>
  89 Y("strip-nondebug", "Strip all symbols, except dbg symbols, from a module");
  90
  91 ModulePass *llvm::createStripNonDebugSymbolsPass() {
  92   return new StripNonDebugSymbols();
  93 }
  94
  95 char StripDebugDeclare::ID = 0;
  96 static RegisterPass<StripDebugDeclare>
  97 Z("strip-debug-declare", "Strip all llvm.dbg.declare intrinsics");
  98
  99 ModulePass *llvm::createStripDebugDeclarePass() {
 100   return new StripDebugDeclare();
 101 }
 102
 103 /// OnlyUsedBy - Return true if V is only used by Usr.
 104 static bool OnlyUsedBy(Value *V, Value *Usr) {
 105   for(Value::use_iterator I = V->use_begin(), E = V->use_end(); I != E; ++I) {
 106     User *U = *I;
 107     if (U != Usr)
 108       return false;
 109   }
 110   return true;
 111 }
 112
 113 static void RemoveDeadConstant(Constant *C) {
 114   assert(C->use_empty() && "Constant is not dead!");
 115   SmallPtrSet<Constant *, 4> Operands;
 116   for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i)
 117     if (isa<DerivedType>(C->getOperand(i)->getType()) &&
 118         OnlyUsedBy(C->getOperand(i), C))
 119       Operands.insert(C->getOperand(i));
 120   if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
 121     if (!GV->hasLocalLinkage()) return;   // Don't delete non static globals.
 122     GV->eraseFromParent();
 123   }
 124   else if (!isa<Function>(C))
 125     if (isa<CompositeType>(C->getType()))
 126       C->destroyConstant();
 127
 128   // If the constant referenced anything, see if we can delete it as well.
 129   for (SmallPtrSet<Constant *, 4>::iterator OI = Operands.begin(),
 130          OE = Operands.end(); OI != OE; ++OI)
 131     RemoveDeadConstant(*OI);
 132 }
 133
 134 // Strip the symbol table of its names.
 135 //
 136 static void StripSymtab(ValueSymbolTable &ST, bool PreserveDbgInfo) {
 137   for (ValueSymbolTable::iterator VI = ST.begin(), VE = ST.end(); VI != VE; ) {
 138     Value *V = VI->getValue();
 139     ++VI;
 140     if (!isa<GlobalValue>(V) || cast<GlobalValue>(V)->hasLocalLinkage()) {
 141       if (!PreserveDbgInfo || !V->getName().startswith("llvm.dbg"))
 142         // Set name to "", removing from symbol table!
 143         V->setName("");
 144     }
 145   }
 146 }
 147
 148 // Strip the symbol table of its names.
 149 static void StripTypeSymtab(TypeSymbolTable &ST, bool PreserveDbgInfo) {
 150   for (TypeSymbolTable::iterator TI = ST.begin(), E = ST.end(); TI != E; ) {
 151     if (PreserveDbgInfo && strncmp(TI->first.c_str(), "llvm.dbg", 8) == 0)
 152       ++TI;
 153     else
 154       ST.remove(TI++);
 155   }
 156 }
 157
 158 /// Find values that are marked as llvm.used.
 159 static void findUsedValues(GlobalVariable *LLVMUsed,
 160                            SmallPtrSet<const GlobalValue*, 8> &UsedValues) {
 161   if (LLVMUsed == 0) return;
 162   UsedValues.insert(LLVMUsed);
 163
 164   ConstantArray *Inits = dyn_cast<ConstantArray>(LLVMUsed->getInitializer());
 165   if (Inits == 0) return;
 166
 167   for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i)
 168     if (GlobalValue *GV =
 169           dyn_cast<GlobalValue>(Inits->getOperand(i)->stripPointerCasts()))
 170       UsedValues.insert(GV);
 171 }
 172
 173 /// StripSymbolNames - Strip symbol names.
 174 static bool StripSymbolNames(Module &M, bool PreserveDbgInfo) {
 175
 176   SmallPtrSet<const GlobalValue*, 8> llvmUsedValues;
 177   findUsedValues(M.getGlobalVariable("llvm.used"), llvmUsedValues);
 178   findUsedValues(M.getGlobalVariable("llvm.compiler.used"), llvmUsedValues);
 179
 180   for (Module::global_iterator I = M.global_begin(), E = M.global_end();
 181        I != E; ++I) {
 182     if (I->hasLocalLinkage() && llvmUsedValues.count(I) == 0)
 183       if (!PreserveDbgInfo || !I->getName().startswith("llvm.dbg"))
 184         I->setName("");     // Internal symbols can't participate in linkage
 185   }
 186
 187   for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
 188     if (I->hasLocalLinkage() && llvmUsedValues.count(I) == 0)
 189       if (!PreserveDbgInfo || !I->getName().startswith("llvm.dbg"))
 190         I->setName("");     // Internal symbols can't participate in linkage
 191     StripSymtab(I->getValueSymbolTable(), PreserveDbgInfo);
 192   }
 193
 194   // Remove all names from types.
 195   StripTypeSymtab(M.getTypeSymbolTable(), PreserveDbgInfo);
 196
 197   return true;
 198 }
 199
 200 // StripDebugInfo - Strip debug info in the module if it exists.
 201 // To do this, we remove llvm.dbg.func.start, llvm.dbg.stoppoint, and
 202 // llvm.dbg.region.end calls, and any globals they point to if now dead.
 203 static bool StripDebugInfo(Module &M) {
 204
 205   // Remove all of the calls to the debugger intrinsics, and remove them from
 206   // the module.
 207   Function *FuncStart = M.getFunction("llvm.dbg.func.start");
 208   Function *StopPoint = M.getFunction("llvm.dbg.stoppoint");
 209   Function *RegionStart = M.getFunction("llvm.dbg.region.start");
 210   Function *RegionEnd = M.getFunction("llvm.dbg.region.end");
 211   Function *Declare = M.getFunction("llvm.dbg.declare");
 212
 213   if (FuncStart) {
 214     while (!FuncStart->use_empty()) {
 215       CallInst *CI = cast<CallInst>(FuncStart->use_back());
 216       CI->eraseFromParent();
 217     }
 218     FuncStart->eraseFromParent();
 219   }
 220   if (StopPoint) {
 221     while (!StopPoint->use_empty()) {
 222       CallInst *CI = cast<CallInst>(StopPoint->use_back());
 223       CI->eraseFromParent();
 224     }
 225     StopPoint->eraseFromParent();
 226   }
 227   if (RegionStart) {
 228     while (!RegionStart->use_empty()) {
 229       CallInst *CI = cast<CallInst>(RegionStart->use_back());
 230       CI->eraseFromParent();
 231     }
 232     RegionStart->eraseFromParent();
 233   }
 234   if (RegionEnd) {
 235     while (!RegionEnd->use_empty()) {
 236       CallInst *CI = cast<CallInst>(RegionEnd->use_back());
 237       CI->eraseFromParent();
 238     }
 239     RegionEnd->eraseFromParent();
 240   }
 241   if (Declare) {
 242     while (!Declare->use_empty()) {
 243       CallInst *CI = cast<CallInst>(Declare->use_back());
 244       CI->eraseFromParent();
 245     }
 246     Declare->eraseFromParent();
 247   }
 248
 249   NamedMDNode *NMD = M.getNamedMetadata("llvm.dbg.gv");
 250   if (NMD)
 251     NMD->eraseFromParent();
 252
 253   // Remove dead metadata.
 254   M.getContext().RemoveDeadMetadata();
 255   return true;
 256 }
 257
 258 bool StripSymbols::runOnModule(Module &M) {
 259   bool Changed = false;
 260   Changed |= StripDebugInfo(M);
 261   if (!OnlyDebugInfo)
 262     Changed |= StripSymbolNames(M, false);
 263   return Changed;
 264 }
 265
 266 bool StripNonDebugSymbols::runOnModule(Module &M) {
 267   return StripSymbolNames(M, true);
 268 }
 269
 270 bool StripDebugDeclare::runOnModule(Module &M) {
 271
 272   Function *Declare = M.getFunction("llvm.dbg.declare");
 273   std::vector<Constant*> DeadConstants;
 274
 275   if (Declare) {
 276     while (!Declare->use_empty()) {
 277       CallInst *CI = cast<CallInst>(Declare->use_back());
 278       Value *Arg1 = CI->getOperand(1);
 279       Value *Arg2 = CI->getOperand(2);
 280       assert(CI->use_empty() && "llvm.dbg intrinsic should have void result");
 281       CI->eraseFromParent();
 282       if (Arg1->use_empty()) {
 283         if (Constant *C = dyn_cast<Constant>(Arg1))
 284           DeadConstants.push_back(C);
 285         else
 286           RecursivelyDeleteTriviallyDeadInstructions(Arg1);
 287       }
 288       if (Arg2->use_empty())
 289         if (Constant *C = dyn_cast<Constant>(Arg2))
 290           DeadConstants.push_back(C);
 291     }
 292     Declare->eraseFromParent();
 293   }
 294
 295   // Delete all llvm.dbg.global_variables.
 296   for (Module::global_iterator I = M.global_begin(), E = M.global_end();
 297        I != E; ++I) {
 298     GlobalVariable *GV = dyn_cast<GlobalVariable>(I);
 299     if (!GV) continue;
 300     if (GV->use_empty() && GV->getName().startswith("llvm.dbg.global_variable"))
 301       DeadConstants.push_back(GV);
 302   }
 303
 304   while (!DeadConstants.empty()) {
 305     Constant *C = DeadConstants.back();
 306     DeadConstants.pop_back();
 307     if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
 308       if (GV->hasLocalLinkage())
 309         RemoveDeadConstant(GV);
 310     }
 311     else
 312       RemoveDeadConstant(C);
 313   }
 314
 315   return true;
 316 }