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      1 //===-- SanitizerCoverage.cpp - coverage instrumentation for sanitizers ---===//
      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 // Coverage instrumentation that works with AddressSanitizer
     11 // and potentially with other Sanitizers.
     12 //
     13 // We create a Guard variable with the same linkage
     14 // as the function and inject this code into the entry block (SCK_Function)
     15 // or all blocks (SCK_BB):
     16 // if (Guard < 0) {
     17 //    __sanitizer_cov(&Guard);
     18 // }
     19 // The accesses to Guard are atomic. The rest of the logic is
     20 // in __sanitizer_cov (it's fine to call it more than once).
     21 //
     22 // With SCK_Edge we also split critical edges this effectively
     23 // instrumenting all edges.
     24 //
     25 // This coverage implementation provides very limited data:
     26 // it only tells if a given function (block) was ever executed. No counters.
     27 // But for many use cases this is what we need and the added slowdown small.
     28 //
     29 //===----------------------------------------------------------------------===//
     30 
     31 #include "llvm/Transforms/Instrumentation.h"
     32 #include "llvm/ADT/ArrayRef.h"
     33 #include "llvm/ADT/SmallVector.h"
     34 #include "llvm/Analysis/EHPersonalities.h"
     35 #include "llvm/IR/CallSite.h"
     36 #include "llvm/IR/DataLayout.h"
     37 #include "llvm/IR/DebugInfo.h"
     38 #include "llvm/IR/Function.h"
     39 #include "llvm/IR/IRBuilder.h"
     40 #include "llvm/IR/InlineAsm.h"
     41 #include "llvm/IR/LLVMContext.h"
     42 #include "llvm/IR/MDBuilder.h"
     43 #include "llvm/IR/Module.h"
     44 #include "llvm/IR/Type.h"
     45 #include "llvm/Support/CommandLine.h"
     46 #include "llvm/Support/Debug.h"
     47 #include "llvm/Support/raw_ostream.h"
     48 #include "llvm/Transforms/Scalar.h"
     49 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
     50 #include "llvm/Transforms/Utils/ModuleUtils.h"
     51 
     52 using namespace llvm;
     53 
     54 #define DEBUG_TYPE "sancov"
     55 
     56 static const char *const kSanCovModuleInitName = "__sanitizer_cov_module_init";
     57 static const char *const kSanCovName = "__sanitizer_cov";
     58 static const char *const kSanCovWithCheckName = "__sanitizer_cov_with_check";
     59 static const char *const kSanCovIndirCallName = "__sanitizer_cov_indir_call16";
     60 static const char *const kSanCovTraceEnter = "__sanitizer_cov_trace_func_enter";
     61 static const char *const kSanCovTraceBB = "__sanitizer_cov_trace_basic_block";
     62 static const char *const kSanCovTraceCmp = "__sanitizer_cov_trace_cmp";
     63 static const char *const kSanCovTraceSwitch = "__sanitizer_cov_trace_switch";
     64 static const char *const kSanCovModuleCtorName = "sancov.module_ctor";
     65 static const uint64_t    kSanCtorAndDtorPriority = 2;
     66 
     67 static cl::opt<int> ClCoverageLevel("sanitizer-coverage-level",
     68        cl::desc("Sanitizer Coverage. 0: none, 1: entry block, 2: all blocks, "
     69                 "3: all blocks and critical edges, "
     70                 "4: above plus indirect calls"),
     71        cl::Hidden, cl::init(0));
     72 
     73 static cl::opt<unsigned> ClCoverageBlockThreshold(
     74     "sanitizer-coverage-block-threshold",
     75     cl::desc("Use a callback with a guard check inside it if there are"
     76              " more than this number of blocks."),
     77     cl::Hidden, cl::init(500));
     78 
     79 static cl::opt<bool>
     80     ClExperimentalTracing("sanitizer-coverage-experimental-tracing",
     81                           cl::desc("Experimental basic-block tracing: insert "
     82                                    "callbacks at every basic block"),
     83                           cl::Hidden, cl::init(false));
     84 
     85 static cl::opt<bool>
     86     ClExperimentalCMPTracing("sanitizer-coverage-experimental-trace-compares",
     87                              cl::desc("Experimental tracing of CMP and similar "
     88                                       "instructions"),
     89                              cl::Hidden, cl::init(false));
     90 
     91 // Experimental 8-bit counters used as an additional search heuristic during
     92 // coverage-guided fuzzing.
     93 // The counters are not thread-friendly:
     94 //   - contention on these counters may cause significant slowdown;
     95 //   - the counter updates are racy and the results may be inaccurate.
     96 // They are also inaccurate due to 8-bit integer overflow.
     97 static cl::opt<bool> ClUse8bitCounters("sanitizer-coverage-8bit-counters",
     98                                        cl::desc("Experimental 8-bit counters"),
     99                                        cl::Hidden, cl::init(false));
    100 
    101 namespace {
    102 
    103 SanitizerCoverageOptions getOptions(int LegacyCoverageLevel) {
    104   SanitizerCoverageOptions Res;
    105   switch (LegacyCoverageLevel) {
    106   case 0:
    107     Res.CoverageType = SanitizerCoverageOptions::SCK_None;
    108     break;
    109   case 1:
    110     Res.CoverageType = SanitizerCoverageOptions::SCK_Function;
    111     break;
    112   case 2:
    113     Res.CoverageType = SanitizerCoverageOptions::SCK_BB;
    114     break;
    115   case 3:
    116     Res.CoverageType = SanitizerCoverageOptions::SCK_Edge;
    117     break;
    118   case 4:
    119     Res.CoverageType = SanitizerCoverageOptions::SCK_Edge;
    120     Res.IndirectCalls = true;
    121     break;
    122   }
    123   return Res;
    124 }
    125 
    126 SanitizerCoverageOptions OverrideFromCL(SanitizerCoverageOptions Options) {
    127   // Sets CoverageType and IndirectCalls.
    128   SanitizerCoverageOptions CLOpts = getOptions(ClCoverageLevel);
    129   Options.CoverageType = std::max(Options.CoverageType, CLOpts.CoverageType);
    130   Options.IndirectCalls |= CLOpts.IndirectCalls;
    131   Options.TraceBB |= ClExperimentalTracing;
    132   Options.TraceCmp |= ClExperimentalCMPTracing;
    133   Options.Use8bitCounters |= ClUse8bitCounters;
    134   return Options;
    135 }
    136 
    137 class SanitizerCoverageModule : public ModulePass {
    138  public:
    139   SanitizerCoverageModule(
    140       const SanitizerCoverageOptions &Options = SanitizerCoverageOptions())
    141       : ModulePass(ID), Options(OverrideFromCL(Options)) {}
    142   bool runOnModule(Module &M) override;
    143   bool runOnFunction(Function &F);
    144   static char ID;  // Pass identification, replacement for typeid
    145   const char *getPassName() const override {
    146     return "SanitizerCoverageModule";
    147   }
    148 
    149  private:
    150   void InjectCoverageForIndirectCalls(Function &F,
    151                                       ArrayRef<Instruction *> IndirCalls);
    152   void InjectTraceForCmp(Function &F, ArrayRef<Instruction *> CmpTraceTargets);
    153   void InjectTraceForSwitch(Function &F,
    154                             ArrayRef<Instruction *> SwitchTraceTargets);
    155   bool InjectCoverage(Function &F, ArrayRef<BasicBlock *> AllBlocks);
    156   void SetNoSanitizeMetadata(Instruction *I);
    157   void InjectCoverageAtBlock(Function &F, BasicBlock &BB, bool UseCalls);
    158   unsigned NumberOfInstrumentedBlocks() {
    159     return SanCovFunction->getNumUses() +
    160            SanCovWithCheckFunction->getNumUses() + SanCovTraceBB->getNumUses() +
    161            SanCovTraceEnter->getNumUses();
    162   }
    163   Function *SanCovFunction;
    164   Function *SanCovWithCheckFunction;
    165   Function *SanCovIndirCallFunction;
    166   Function *SanCovTraceEnter, *SanCovTraceBB;
    167   Function *SanCovTraceCmpFunction;
    168   Function *SanCovTraceSwitchFunction;
    169   InlineAsm *EmptyAsm;
    170   Type *IntptrTy, *Int64Ty, *Int64PtrTy;
    171   Module *CurModule;
    172   LLVMContext *C;
    173   const DataLayout *DL;
    174 
    175   GlobalVariable *GuardArray;
    176   GlobalVariable *EightBitCounterArray;
    177 
    178   SanitizerCoverageOptions Options;
    179 };
    180 
    181 }  // namespace
    182 
    183 bool SanitizerCoverageModule::runOnModule(Module &M) {
    184   if (Options.CoverageType == SanitizerCoverageOptions::SCK_None)
    185     return false;
    186   C = &(M.getContext());
    187   DL = &M.getDataLayout();
    188   CurModule = &M;
    189   IntptrTy = Type::getIntNTy(*C, DL->getPointerSizeInBits());
    190   Type *VoidTy = Type::getVoidTy(*C);
    191   IRBuilder<> IRB(*C);
    192   Type *Int8PtrTy = PointerType::getUnqual(IRB.getInt8Ty());
    193   Type *Int32PtrTy = PointerType::getUnqual(IRB.getInt32Ty());
    194   Int64PtrTy = PointerType::getUnqual(IRB.getInt64Ty());
    195   Int64Ty = IRB.getInt64Ty();
    196 
    197   SanCovFunction = checkSanitizerInterfaceFunction(
    198       M.getOrInsertFunction(kSanCovName, VoidTy, Int32PtrTy, nullptr));
    199   SanCovWithCheckFunction = checkSanitizerInterfaceFunction(
    200       M.getOrInsertFunction(kSanCovWithCheckName, VoidTy, Int32PtrTy, nullptr));
    201   SanCovIndirCallFunction =
    202       checkSanitizerInterfaceFunction(M.getOrInsertFunction(
    203           kSanCovIndirCallName, VoidTy, IntptrTy, IntptrTy, nullptr));
    204   SanCovTraceCmpFunction =
    205       checkSanitizerInterfaceFunction(M.getOrInsertFunction(
    206           kSanCovTraceCmp, VoidTy, Int64Ty, Int64Ty, Int64Ty, nullptr));
    207   SanCovTraceSwitchFunction =
    208       checkSanitizerInterfaceFunction(M.getOrInsertFunction(
    209           kSanCovTraceSwitch, VoidTy, Int64Ty, Int64PtrTy, nullptr));
    210 
    211   // We insert an empty inline asm after cov callbacks to avoid callback merge.
    212   EmptyAsm = InlineAsm::get(FunctionType::get(IRB.getVoidTy(), false),
    213                             StringRef(""), StringRef(""),
    214                             /*hasSideEffects=*/true);
    215 
    216   SanCovTraceEnter = checkSanitizerInterfaceFunction(
    217       M.getOrInsertFunction(kSanCovTraceEnter, VoidTy, Int32PtrTy, nullptr));
    218   SanCovTraceBB = checkSanitizerInterfaceFunction(
    219       M.getOrInsertFunction(kSanCovTraceBB, VoidTy, Int32PtrTy, nullptr));
    220 
    221   // At this point we create a dummy array of guards because we don't
    222   // know how many elements we will need.
    223   Type *Int32Ty = IRB.getInt32Ty();
    224   Type *Int8Ty = IRB.getInt8Ty();
    225 
    226   GuardArray =
    227       new GlobalVariable(M, Int32Ty, false, GlobalValue::ExternalLinkage,
    228                          nullptr, "__sancov_gen_cov_tmp");
    229   if (Options.Use8bitCounters)
    230     EightBitCounterArray =
    231         new GlobalVariable(M, Int8Ty, false, GlobalVariable::ExternalLinkage,
    232                            nullptr, "__sancov_gen_cov_tmp");
    233 
    234   for (auto &F : M)
    235     runOnFunction(F);
    236 
    237   auto N = NumberOfInstrumentedBlocks();
    238 
    239   // Now we know how many elements we need. Create an array of guards
    240   // with one extra element at the beginning for the size.
    241   Type *Int32ArrayNTy = ArrayType::get(Int32Ty, N + 1);
    242   GlobalVariable *RealGuardArray = new GlobalVariable(
    243       M, Int32ArrayNTy, false, GlobalValue::PrivateLinkage,
    244       Constant::getNullValue(Int32ArrayNTy), "__sancov_gen_cov");
    245 
    246 
    247   // Replace the dummy array with the real one.
    248   GuardArray->replaceAllUsesWith(
    249       IRB.CreatePointerCast(RealGuardArray, Int32PtrTy));
    250   GuardArray->eraseFromParent();
    251 
    252   GlobalVariable *RealEightBitCounterArray;
    253   if (Options.Use8bitCounters) {
    254     // Make sure the array is 16-aligned.
    255     static const int kCounterAlignment = 16;
    256     Type *Int8ArrayNTy =
    257         ArrayType::get(Int8Ty, RoundUpToAlignment(N, kCounterAlignment));
    258     RealEightBitCounterArray = new GlobalVariable(
    259         M, Int8ArrayNTy, false, GlobalValue::PrivateLinkage,
    260         Constant::getNullValue(Int8ArrayNTy), "__sancov_gen_cov_counter");
    261     RealEightBitCounterArray->setAlignment(kCounterAlignment);
    262     EightBitCounterArray->replaceAllUsesWith(
    263         IRB.CreatePointerCast(RealEightBitCounterArray, Int8PtrTy));
    264     EightBitCounterArray->eraseFromParent();
    265   }
    266 
    267   // Create variable for module (compilation unit) name
    268   Constant *ModNameStrConst =
    269       ConstantDataArray::getString(M.getContext(), M.getName(), true);
    270   GlobalVariable *ModuleName =
    271       new GlobalVariable(M, ModNameStrConst->getType(), true,
    272                          GlobalValue::PrivateLinkage, ModNameStrConst);
    273 
    274   Function *CtorFunc;
    275   std::tie(CtorFunc, std::ignore) = createSanitizerCtorAndInitFunctions(
    276       M, kSanCovModuleCtorName, kSanCovModuleInitName,
    277       {Int32PtrTy, IntptrTy, Int8PtrTy, Int8PtrTy},
    278       {IRB.CreatePointerCast(RealGuardArray, Int32PtrTy),
    279        ConstantInt::get(IntptrTy, N),
    280        Options.Use8bitCounters
    281            ? IRB.CreatePointerCast(RealEightBitCounterArray, Int8PtrTy)
    282            : Constant::getNullValue(Int8PtrTy),
    283        IRB.CreatePointerCast(ModuleName, Int8PtrTy)});
    284 
    285   appendToGlobalCtors(M, CtorFunc, kSanCtorAndDtorPriority);
    286 
    287   return true;
    288 }
    289 
    290 bool SanitizerCoverageModule::runOnFunction(Function &F) {
    291   if (F.empty()) return false;
    292   if (F.getName().find(".module_ctor") != std::string::npos)
    293     return false;  // Should not instrument sanitizer init functions.
    294   // Don't instrument functions using SEH for now. Splitting basic blocks like
    295   // we do for coverage breaks WinEHPrepare.
    296   // FIXME: Remove this when SEH no longer uses landingpad pattern matching.
    297   if (F.hasPersonalityFn() &&
    298       isAsynchronousEHPersonality(classifyEHPersonality(F.getPersonalityFn())))
    299     return false;
    300   if (Options.CoverageType >= SanitizerCoverageOptions::SCK_Edge)
    301     SplitAllCriticalEdges(F);
    302   SmallVector<Instruction*, 8> IndirCalls;
    303   SmallVector<BasicBlock*, 16> AllBlocks;
    304   SmallVector<Instruction*, 8> CmpTraceTargets;
    305   SmallVector<Instruction*, 8> SwitchTraceTargets;
    306   for (auto &BB : F) {
    307     AllBlocks.push_back(&BB);
    308     for (auto &Inst : BB) {
    309       if (Options.IndirectCalls) {
    310         CallSite CS(&Inst);
    311         if (CS && !CS.getCalledFunction())
    312           IndirCalls.push_back(&Inst);
    313       }
    314       if (Options.TraceCmp) {
    315         if (isa<ICmpInst>(&Inst))
    316           CmpTraceTargets.push_back(&Inst);
    317         if (isa<SwitchInst>(&Inst))
    318           SwitchTraceTargets.push_back(&Inst);
    319       }
    320     }
    321   }
    322   InjectCoverage(F, AllBlocks);
    323   InjectCoverageForIndirectCalls(F, IndirCalls);
    324   InjectTraceForCmp(F, CmpTraceTargets);
    325   InjectTraceForSwitch(F, SwitchTraceTargets);
    326   return true;
    327 }
    328 
    329 bool SanitizerCoverageModule::InjectCoverage(Function &F,
    330                                              ArrayRef<BasicBlock *> AllBlocks) {
    331   switch (Options.CoverageType) {
    332   case SanitizerCoverageOptions::SCK_None:
    333     return false;
    334   case SanitizerCoverageOptions::SCK_Function:
    335     InjectCoverageAtBlock(F, F.getEntryBlock(), false);
    336     return true;
    337   default: {
    338     bool UseCalls = ClCoverageBlockThreshold < AllBlocks.size();
    339     for (auto BB : AllBlocks)
    340       InjectCoverageAtBlock(F, *BB, UseCalls);
    341     return true;
    342   }
    343   }
    344 }
    345 
    346 // On every indirect call we call a run-time function
    347 // __sanitizer_cov_indir_call* with two parameters:
    348 //   - callee address,
    349 //   - global cache array that contains kCacheSize pointers (zero-initialized).
    350 //     The cache is used to speed up recording the caller-callee pairs.
    351 // The address of the caller is passed implicitly via caller PC.
    352 // kCacheSize is encoded in the name of the run-time function.
    353 void SanitizerCoverageModule::InjectCoverageForIndirectCalls(
    354     Function &F, ArrayRef<Instruction *> IndirCalls) {
    355   if (IndirCalls.empty()) return;
    356   const int kCacheSize = 16;
    357   const int kCacheAlignment = 64;  // Align for better performance.
    358   Type *Ty = ArrayType::get(IntptrTy, kCacheSize);
    359   for (auto I : IndirCalls) {
    360     IRBuilder<> IRB(I);
    361     CallSite CS(I);
    362     Value *Callee = CS.getCalledValue();
    363     if (isa<InlineAsm>(Callee)) continue;
    364     GlobalVariable *CalleeCache = new GlobalVariable(
    365         *F.getParent(), Ty, false, GlobalValue::PrivateLinkage,
    366         Constant::getNullValue(Ty), "__sancov_gen_callee_cache");
    367     CalleeCache->setAlignment(kCacheAlignment);
    368     IRB.CreateCall(SanCovIndirCallFunction,
    369                    {IRB.CreatePointerCast(Callee, IntptrTy),
    370                     IRB.CreatePointerCast(CalleeCache, IntptrTy)});
    371   }
    372 }
    373 
    374 // For every switch statement we insert a call:
    375 // __sanitizer_cov_trace_switch(CondValue,
    376 //      {NumCases, ValueSizeInBits, Case0Value, Case1Value, Case2Value, ... })
    377 
    378 void SanitizerCoverageModule::InjectTraceForSwitch(
    379     Function &F, ArrayRef<Instruction *> SwitchTraceTargets) {
    380   for (auto I : SwitchTraceTargets) {
    381     if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) {
    382       IRBuilder<> IRB(I);
    383       SmallVector<Constant *, 16> Initializers;
    384       Value *Cond = SI->getCondition();
    385       if (Cond->getType()->getScalarSizeInBits() >
    386           Int64Ty->getScalarSizeInBits())
    387         continue;
    388       Initializers.push_back(ConstantInt::get(Int64Ty, SI->getNumCases()));
    389       Initializers.push_back(
    390           ConstantInt::get(Int64Ty, Cond->getType()->getScalarSizeInBits()));
    391       if (Cond->getType()->getScalarSizeInBits() <
    392           Int64Ty->getScalarSizeInBits())
    393         Cond = IRB.CreateIntCast(Cond, Int64Ty, false);
    394       for (auto It: SI->cases()) {
    395         Constant *C = It.getCaseValue();
    396         if (C->getType()->getScalarSizeInBits() <
    397             Int64Ty->getScalarSizeInBits())
    398           C = ConstantExpr::getCast(CastInst::ZExt, It.getCaseValue(), Int64Ty);
    399         Initializers.push_back(C);
    400       }
    401       ArrayType *ArrayOfInt64Ty = ArrayType::get(Int64Ty, Initializers.size());
    402       GlobalVariable *GV = new GlobalVariable(
    403           *CurModule, ArrayOfInt64Ty, false, GlobalVariable::InternalLinkage,
    404           ConstantArray::get(ArrayOfInt64Ty, Initializers),
    405           "__sancov_gen_cov_switch_values");
    406       IRB.CreateCall(SanCovTraceSwitchFunction,
    407                      {Cond, IRB.CreatePointerCast(GV, Int64PtrTy)});
    408     }
    409   }
    410 }
    411 
    412 
    413 void SanitizerCoverageModule::InjectTraceForCmp(
    414     Function &F, ArrayRef<Instruction *> CmpTraceTargets) {
    415   for (auto I : CmpTraceTargets) {
    416     if (ICmpInst *ICMP = dyn_cast<ICmpInst>(I)) {
    417       IRBuilder<> IRB(ICMP);
    418       Value *A0 = ICMP->getOperand(0);
    419       Value *A1 = ICMP->getOperand(1);
    420       if (!A0->getType()->isIntegerTy()) continue;
    421       uint64_t TypeSize = DL->getTypeStoreSizeInBits(A0->getType());
    422       // __sanitizer_cov_trace_cmp((type_size << 32) | predicate, A0, A1);
    423       IRB.CreateCall(
    424           SanCovTraceCmpFunction,
    425           {ConstantInt::get(Int64Ty, (TypeSize << 32) | ICMP->getPredicate()),
    426            IRB.CreateIntCast(A0, Int64Ty, true),
    427            IRB.CreateIntCast(A1, Int64Ty, true)});
    428     }
    429   }
    430 }
    431 
    432 void SanitizerCoverageModule::SetNoSanitizeMetadata(Instruction *I) {
    433   I->setMetadata(
    434       I->getModule()->getMDKindID("nosanitize"), MDNode::get(*C, None));
    435 }
    436 
    437 void SanitizerCoverageModule::InjectCoverageAtBlock(Function &F, BasicBlock &BB,
    438                                                     bool UseCalls) {
    439   // Don't insert coverage for unreachable blocks: we will never call
    440   // __sanitizer_cov() for them, so counting them in
    441   // NumberOfInstrumentedBlocks() might complicate calculation of code coverage
    442   // percentage. Also, unreachable instructions frequently have no debug
    443   // locations.
    444   if (isa<UnreachableInst>(BB.getTerminator()))
    445     return;
    446   BasicBlock::iterator IP = BB.getFirstInsertionPt();
    447 
    448   bool IsEntryBB = &BB == &F.getEntryBlock();
    449   DebugLoc EntryLoc;
    450   if (IsEntryBB) {
    451     if (auto SP = getDISubprogram(&F))
    452       EntryLoc = DebugLoc::get(SP->getScopeLine(), 0, SP);
    453     // Keep static allocas and llvm.localescape calls in the entry block.  Even
    454     // if we aren't splitting the block, it's nice for allocas to be before
    455     // calls.
    456     IP = PrepareToSplitEntryBlock(BB, IP);
    457   } else {
    458     EntryLoc = IP->getDebugLoc();
    459   }
    460 
    461   IRBuilder<> IRB(&*IP);
    462   IRB.SetCurrentDebugLocation(EntryLoc);
    463   Value *GuardP = IRB.CreateAdd(
    464       IRB.CreatePointerCast(GuardArray, IntptrTy),
    465       ConstantInt::get(IntptrTy, (1 + NumberOfInstrumentedBlocks()) * 4));
    466   Type *Int32PtrTy = PointerType::getUnqual(IRB.getInt32Ty());
    467   GuardP = IRB.CreateIntToPtr(GuardP, Int32PtrTy);
    468   if (Options.TraceBB) {
    469     IRB.CreateCall(IsEntryBB ? SanCovTraceEnter : SanCovTraceBB, GuardP);
    470   } else if (UseCalls) {
    471     IRB.CreateCall(SanCovWithCheckFunction, GuardP);
    472   } else {
    473     LoadInst *Load = IRB.CreateLoad(GuardP);
    474     Load->setAtomic(Monotonic);
    475     Load->setAlignment(4);
    476     SetNoSanitizeMetadata(Load);
    477     Value *Cmp = IRB.CreateICmpSGE(Constant::getNullValue(Load->getType()), Load);
    478     Instruction *Ins = SplitBlockAndInsertIfThen(
    479         Cmp, &*IP, false, MDBuilder(*C).createBranchWeights(1, 100000));
    480     IRB.SetInsertPoint(Ins);
    481     IRB.SetCurrentDebugLocation(EntryLoc);
    482     // __sanitizer_cov gets the PC of the instruction using GET_CALLER_PC.
    483     IRB.CreateCall(SanCovFunction, GuardP);
    484     IRB.CreateCall(EmptyAsm, {}); // Avoids callback merge.
    485   }
    486 
    487   if (Options.Use8bitCounters) {
    488     IRB.SetInsertPoint(&*IP);
    489     Value *P = IRB.CreateAdd(
    490         IRB.CreatePointerCast(EightBitCounterArray, IntptrTy),
    491         ConstantInt::get(IntptrTy, NumberOfInstrumentedBlocks() - 1));
    492     P = IRB.CreateIntToPtr(P, IRB.getInt8PtrTy());
    493     LoadInst *LI = IRB.CreateLoad(P);
    494     Value *Inc = IRB.CreateAdd(LI, ConstantInt::get(IRB.getInt8Ty(), 1));
    495     StoreInst *SI = IRB.CreateStore(Inc, P);
    496     SetNoSanitizeMetadata(LI);
    497     SetNoSanitizeMetadata(SI);
    498   }
    499 }
    500 
    501 char SanitizerCoverageModule::ID = 0;
    502 INITIALIZE_PASS(SanitizerCoverageModule, "sancov",
    503     "SanitizerCoverage: TODO."
    504     "ModulePass", false, false)
    505 ModulePass *llvm::createSanitizerCoverageModulePass(
    506     const SanitizerCoverageOptions &Options) {
    507   return new SanitizerCoverageModule(Options);
    508 }
    509