tools/bugpoint/CrashDebugger.cpp

//===- CrashDebugger.cpp - Debug compilation crashes ----------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the bugpoint internals that narrow down compilation crashes
//
//===----------------------------------------------------------------------===//

#include "BugDriver.h"
#include "ListReducer.h"
#include "ToolRunner.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/StringSet.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/LegacyPassManager.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/ValueSymbolTable.h"
#include "llvm/IR/Verifier.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/FileUtilities.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include <set>
using namespace llvm;

namespace {
  cl::opt<bool>
  KeepMain("keep-main",
           cl::desc("Force function reduction to keep main"),
           cl::init(false));
  cl::opt<bool>
  NoGlobalRM ("disable-global-remove",
         cl::desc("Do not remove global variables"),
         cl::init(false));

  cl::opt<bool>
  ReplaceFuncsWithNull("replace-funcs-with-null",
         cl::desc("When stubbing functions, replace all uses will null"),
         cl::init(false));
  cl::opt<bool>
  DontReducePassList("disable-pass-list-reduction",
                     cl::desc("Skip pass list reduction steps"),
                     cl::init(false));

  cl::opt<bool> NoNamedMDRM("disable-namedmd-remove",
                            cl::desc("Do not remove global named metadata"),
                            cl::init(false));
}

namespace llvm {
  class ReducePassList : public ListReducer<std::string> {
    BugDriver &BD;
  public:
    ReducePassList(BugDriver &bd) : BD(bd) {}

    // doTest - Return true iff running the "removed" passes succeeds, and
    // running the "Kept" passes fail when run on the output of the "removed"
    // passes.  If we return true, we update the current module of bugpoint.
    //
    TestResult doTest(std::vector<std::string> &Removed,
                      std::vector<std::string> &Kept,
                      std::string &Error) override;
  };
}

ReducePassList::TestResult
ReducePassList::doTest(std::vector<std::string> &Prefix,
                       std::vector<std::string> &Suffix,
                       std::string &Error) {
  std::string PrefixOutput;
  Module *OrigProgram = nullptr;
  if (!Prefix.empty()) {
    outs() << "Checking to see if these passes crash: "
           << getPassesString(Prefix) << ": ";
    if (BD.runPasses(BD.getProgram(), Prefix, PrefixOutput))
      return KeepPrefix;

    OrigProgram = BD.Program;

    BD.Program = parseInputFile(PrefixOutput, BD.getContext()).release();
    if (BD.Program == nullptr) {
      errs() << BD.getToolName() << ": Error reading bitcode file '"
             << PrefixOutput << "'!\n";
      exit(1);
    }
    sys::fs::remove(PrefixOutput);
  }

  outs() << "Checking to see if these passes crash: "
         << getPassesString(Suffix) << ": ";

  if (BD.runPasses(BD.getProgram(), Suffix)) {
    delete OrigProgram;            // The suffix crashes alone...
    return KeepSuffix;
  }

  // Nothing failed, restore state...
  if (OrigProgram) {
    delete BD.Program;
    BD.Program = OrigProgram;
  }
  return NoFailure;
}

namespace {
  /// ReduceCrashingGlobalVariables - This works by removing the global
  /// variable's initializer and seeing if the program still crashes. If it
  /// does, then we keep that program and try again.
  ///
  class ReduceCrashingGlobalVariables : public ListReducer<GlobalVariable*> {
    BugDriver &BD;
    bool (*TestFn)(const BugDriver &, Module *);
  public:
    ReduceCrashingGlobalVariables(BugDriver &bd,
                                  bool (*testFn)(const BugDriver &, Module *))
      : BD(bd), TestFn(testFn) {}

    TestResult doTest(std::vector<GlobalVariable*> &Prefix,
                      std::vector<GlobalVariable*> &Kept,
                      std::string &Error) override {
      if (!Kept.empty() && TestGlobalVariables(Kept))
        return KeepSuffix;
      if (!Prefix.empty() && TestGlobalVariables(Prefix))
        return KeepPrefix;
      return NoFailure;
    }

    bool TestGlobalVariables(std::vector<GlobalVariable*> &GVs);
  };
}

bool
ReduceCrashingGlobalVariables::TestGlobalVariables(
                              std::vector<GlobalVariable*> &GVs) {
  // Clone the program to try hacking it apart...
  ValueToValueMapTy VMap;
  Module *M = CloneModule(BD.getProgram(), VMap).release();

  // Convert list to set for fast lookup...
  std::set<GlobalVariable*> GVSet;

  for (unsigned i = 0, e = GVs.size(); i != e; ++i) {
    GlobalVariable* CMGV = cast<GlobalVariable>(VMap[GVs[i]]);
    assert(CMGV && "Global Variable not in module?!");
    GVSet.insert(CMGV);
  }

  outs() << "Checking for crash with only these global variables: ";
  PrintGlobalVariableList(GVs);
  outs() << ": ";

  // Loop over and delete any global variables which we aren't supposed to be
  // playing with...
  for (GlobalVariable &I : M->globals())
    if (I.hasInitializer() && !GVSet.count(&I)) {
      DeleteGlobalInitializer(&I);
      I.setLinkage(GlobalValue::ExternalLinkage);
    }

  // Try running the hacked up program...
  if (TestFn(BD, M)) {
    BD.setNewProgram(M);        // It crashed, keep the trimmed version...

    // Make sure to use global variable pointers that point into the now-current
    // module.
    GVs.assign(GVSet.begin(), GVSet.end());
    return true;
  }

  delete M;
  return false;
}

namespace {
  /// ReduceCrashingFunctions reducer - This works by removing functions and
  /// seeing if the program still crashes. If it does, then keep the newer,
  /// smaller program.
  ///
  class ReduceCrashingFunctions : public ListReducer<Function*> {
    BugDriver &BD;
    bool (*TestFn)(const BugDriver &, Module *);
  public:
    ReduceCrashingFunctions(BugDriver &bd,
                            bool (*testFn)(const BugDriver &, Module *))
      : BD(bd), TestFn(testFn) {}

    TestResult doTest(std::vector<Function*> &Prefix,
                      std::vector<Function*> &Kept,
                      std::string &Error) override {
      if (!Kept.empty() && TestFuncs(Kept))
        return KeepSuffix;
      if (!Prefix.empty() && TestFuncs(Prefix))
        return KeepPrefix;
      return NoFailure;
    }

    bool TestFuncs(std::vector<Function*> &Prefix);
  };
}

static void RemoveFunctionReferences(Module *M, const char* Name) {
  auto *UsedVar = M->getGlobalVariable(Name, true);
  if (!UsedVar || !UsedVar->hasInitializer()) return;
  if (isa<ConstantAggregateZero>(UsedVar->getInitializer())) {
    assert(UsedVar->use_empty());
    UsedVar->eraseFromParent();
    return;
  }
  auto *OldUsedVal = cast<ConstantArray>(UsedVar->getInitializer());
  std::vector<Constant*> Used;
  for(Value *V : OldUsedVal->operand_values()) {
    Constant *Op = cast<Constant>(V->stripPointerCasts());
    if(!Op->isNullValue()) {
      Used.push_back(cast<Constant>(V));
    }
  }
  auto *NewValElemTy = OldUsedVal->getType()->getElementType();
  auto *NewValTy = ArrayType::get(NewValElemTy, Used.size());
  auto *NewUsedVal = ConstantArray::get(NewValTy, Used);
  UsedVar->mutateType(NewUsedVal->getType()->getPointerTo());
  UsedVar->setInitializer(NewUsedVal);
}

bool ReduceCrashingFunctions::TestFuncs(std::vector<Function*> &Funcs) {
  // If main isn't present, claim there is no problem.
  if (KeepMain && std::find(Funcs.begin(), Funcs.end(),
                            BD.getProgram()->getFunction("main")) ==
                      Funcs.end())
    return false;

  // Clone the program to try hacking it apart...
  ValueToValueMapTy VMap;
  Module *M = CloneModule(BD.getProgram(), VMap).release();

  // Convert list to set for fast lookup...
  std::set<Function*> Functions;
  for (unsigned i = 0, e = Funcs.size(); i != e; ++i) {
    Function *CMF = cast<Function>(VMap[Funcs[i]]);
    assert(CMF && "Function not in module?!");
    assert(CMF->getFunctionType() == Funcs[i]->getFunctionType() && "wrong ty");
    assert(CMF->getName() == Funcs[i]->getName() && "wrong name");
    Functions.insert(CMF);
  }

  outs() << "Checking for crash with only these functions: ";
  PrintFunctionList(Funcs);
  outs() << ": ";
  if (!ReplaceFuncsWithNull) {
    // Loop over and delete any functions which we aren't supposed to be playing
    // with...
    for (Function &I : *M)
      if (!I.isDeclaration() && !Functions.count(&I))
        DeleteFunctionBody(&I);
  } else {
    std::vector<GlobalValue*> ToRemove;
    // First, remove aliases to functions we're about to purge.
    for (GlobalAlias &Alias : M->aliases()) {
      Constant *Root = Alias.getAliasee()->stripPointerCasts();
      Function *F = dyn_cast<Function>(Root);
      if (F) {
        if (Functions.count(F))
          // We're keeping this function.
          continue;
      } else if (Root->isNullValue()) {
        // This referenced a globalalias that we've already replaced,
        // so we still need to replace this alias.
      } else if (!F) {
        // Not a function, therefore not something we mess with.
        continue;
      }

      PointerType *Ty = cast<PointerType>(Alias.getType());
      Constant *Replacement = ConstantPointerNull::get(Ty);
      Alias.replaceAllUsesWith(Replacement);
      ToRemove.push_back(&Alias);
    }

    for (Function &I : *M) {
      if (!I.isDeclaration() && !Functions.count(&I)) {
        PointerType *Ty = cast<PointerType>(I.getType());
        Constant *Replacement = ConstantPointerNull::get(Ty);
        I.replaceAllUsesWith(Replacement);
        ToRemove.push_back(&I);
      }
    }

    for (auto *F : ToRemove) {
      F->eraseFromParent();
    }

    // Finally, remove any null members from any global intrinsic.
    RemoveFunctionReferences(M, "llvm.used");
    RemoveFunctionReferences(M, "llvm.compiler.used");
  }
  // Try running the hacked up program...
  if (TestFn(BD, M)) {
    BD.setNewProgram(M);        // It crashed, keep the trimmed version...

    // Make sure to use function pointers that point into the now-current
    // module.
    Funcs.assign(Functions.begin(), Functions.end());
    return true;
  }
  delete M;
  return false;
}


namespace {
  /// ReduceCrashingBlocks reducer - This works by setting the terminators of
  /// all terminators except the specified basic blocks to a 'ret' instruction,
  /// then running the simplify-cfg pass.  This has the effect of chopping up
  /// the CFG really fast which can reduce large functions quickly.
  ///
  class ReduceCrashingBlocks : public ListReducer<const BasicBlock*> {
    BugDriver &BD;
    bool (*TestFn)(const BugDriver &, Module *);
  public:
    ReduceCrashingBlocks(BugDriver &bd,
                         bool (*testFn)(const BugDriver &, Module *))
      : BD(bd), TestFn(testFn) {}

    TestResult doTest(std::vector<const BasicBlock*> &Prefix,
                      std::vector<const BasicBlock*> &Kept,
                      std::string &Error) override {
      if (!Kept.empty() && TestBlocks(Kept))
        return KeepSuffix;
      if (!Prefix.empty() && TestBlocks(Prefix))
        return KeepPrefix;
      return NoFailure;
    }

    bool TestBlocks(std::vector<const BasicBlock*> &Prefix);
  };
}

bool ReduceCrashingBlocks::TestBlocks(std::vector<const BasicBlock*> &BBs) {
  // Clone the program to try hacking it apart...
  ValueToValueMapTy VMap;
  Module *M = CloneModule(BD.getProgram(), VMap).release();

  // Convert list to set for fast lookup...
  SmallPtrSet<BasicBlock*, 8> Blocks;
  for (unsigned i = 0, e = BBs.size(); i != e; ++i)
    Blocks.insert(cast<BasicBlock>(VMap[BBs[i]]));

  outs() << "Checking for crash with only these blocks:";
  unsigned NumPrint = Blocks.size();
  if (NumPrint > 10) NumPrint = 10;
  for (unsigned i = 0, e = NumPrint; i != e; ++i)
    outs() << " " << BBs[i]->getName();
  if (NumPrint < Blocks.size())
    outs() << "... <" << Blocks.size() << " total>";
  outs() << ": ";

  // Loop over and delete any hack up any blocks that are not listed...
  for (Module::iterator I = M->begin(), E = M->end(); I != E; ++I)
    for (Function::iterator BB = I->begin(), E = I->end(); BB != E; ++BB)
      if (!Blocks.count(&*BB) && BB->getTerminator()->getNumSuccessors()) {
        // Loop over all of the successors of this block, deleting any PHI nodes
        // that might include it.
        for (succ_iterator SI = succ_begin(&*BB), E = succ_end(&*BB); SI != E;
             ++SI)
          (*SI)->removePredecessor(&*BB);

        TerminatorInst *BBTerm = BB->getTerminator();
        if (BBTerm->isEHPad())
          continue;
        if (!BBTerm->getType()->isVoidTy() && !BBTerm->getType()->isTokenTy())
          BBTerm->replaceAllUsesWith(Constant::getNullValue(BBTerm->getType()));

        // Replace the old terminator instruction.
        BB->getInstList().pop_back();
        new UnreachableInst(BB->getContext(), &*BB);
      }

  // The CFG Simplifier pass may delete one of the basic blocks we are
  // interested in.  If it does we need to take the block out of the list.  Make
  // a "persistent mapping" by turning basic blocks into <function, name> pairs.
  // This won't work well if blocks are unnamed, but that is just the risk we
  // have to take.
  std::vector<std::pair<std::string, std::string> > BlockInfo;

  for (BasicBlock *BB : Blocks)
    BlockInfo.emplace_back(BB->getParent()->getName(), BB->getName());

  // Now run the CFG simplify pass on the function...
  std::vector<std::string> Passes;
  Passes.push_back("simplifycfg");
  Passes.push_back("verify");
  std::unique_ptr<Module> New = BD.runPassesOn(M, Passes);
  delete M;
  if (!New) {
    errs() << "simplifycfg failed!\n";
    exit(1);
  }
  M = New.release();

  // Try running on the hacked up program...
  if (TestFn(BD, M)) {
    BD.setNewProgram(M);      // It crashed, keep the trimmed version...

    // Make sure to use basic block pointers that point into the now-current
    // module, and that they don't include any deleted blocks.
    BBs.clear();
    const ValueSymbolTable &GST = M->getValueSymbolTable();
    for (unsigned i = 0, e = BlockInfo.size(); i != e; ++i) {
      Function *F = cast<Function>(GST.lookup(BlockInfo[i].first));
      ValueSymbolTable &ST = F->getValueSymbolTable();
      Value* V = ST.lookup(BlockInfo[i].second);
      if (V && V->getType() == Type::getLabelTy(V->getContext()))
        BBs.push_back(cast<BasicBlock>(V));
    }
    return true;
  }
  delete M;  // It didn't crash, try something else.
  return false;
}

namespace {
  /// ReduceCrashingInstructions reducer - This works by removing the specified
  /// non-terminator instructions and replacing them with undef.
  ///
  class ReduceCrashingInstructions : public ListReducer<const Instruction*> {
    BugDriver &BD;
    bool (*TestFn)(const BugDriver &, Module *);
  public:
    ReduceCrashingInstructions(BugDriver &bd,
                               bool (*testFn)(const BugDriver &, Module *))
      : BD(bd), TestFn(testFn) {}

    TestResult doTest(std::vector<const Instruction*> &Prefix,
                      std::vector<const Instruction*> &Kept,
                      std::string &Error) override {
      if (!Kept.empty() && TestInsts(Kept))
        return KeepSuffix;
      if (!Prefix.empty() && TestInsts(Prefix))
        return KeepPrefix;
      return NoFailure;
    }

    bool TestInsts(std::vector<const Instruction*> &Prefix);
  };
}

bool ReduceCrashingInstructions::TestInsts(std::vector<const Instruction*>
                                           &Insts) {
  // Clone the program to try hacking it apart...
  ValueToValueMapTy VMap;
  Module *M = CloneModule(BD.getProgram(), VMap).release();

  // Convert list to set for fast lookup...
  SmallPtrSet<Instruction*, 64> Instructions;
  for (unsigned i = 0, e = Insts.size(); i != e; ++i) {
    assert(!isa<TerminatorInst>(Insts[i]));
    Instructions.insert(cast<Instruction>(VMap[Insts[i]]));
  }

  outs() << "Checking for crash with only " << Instructions.size();
  if (Instructions.size() == 1)
    outs() << " instruction: ";
  else
    outs() << " instructions: ";

  for (Module::iterator MI = M->begin(), ME = M->end(); MI != ME; ++MI)
    for (Function::iterator FI = MI->begin(), FE = MI->end(); FI != FE; ++FI)
      for (BasicBlock::iterator I = FI->begin(), E = FI->end(); I != E;) {
        Instruction *Inst = &*I++;
        if (!Instructions.count(Inst) && !isa<TerminatorInst>(Inst) &&
            !Inst->isEHPad()) {
          if (!Inst->getType()->isVoidTy() && !Inst->getType()->isTokenTy())
            Inst->replaceAllUsesWith(UndefValue::get(Inst->getType()));
          Inst->eraseFromParent();
        }
      }

  // Verify that this is still valid.
  legacy::PassManager Passes;
  Passes.add(createVerifierPass());
  Passes.run(*M);

  // Try running on the hacked up program...
  if (TestFn(BD, M)) {
    BD.setNewProgram(M);      // It crashed, keep the trimmed version...

    // Make sure to use instruction pointers that point into the now-current
    // module, and that they don't include any deleted blocks.
    Insts.clear();
    for (Instruction *Inst : Instructions)
      Insts.push_back(Inst);
    return true;
  }
  delete M;  // It didn't crash, try something else.
  return false;
}

namespace {
// Reduce the list of Named Metadata nodes. We keep this as a list of
// names to avoid having to convert back and forth every time.
class ReduceCrashingNamedMD : public ListReducer<std::string> {
  BugDriver &BD;
  bool (*TestFn)(const BugDriver &, Module *);

public:
  ReduceCrashingNamedMD(BugDriver &bd,
                        bool (*testFn)(const BugDriver &, Module *))
      : BD(bd), TestFn(testFn) {}

  TestResult doTest(std::vector<std::string> &Prefix,
                    std::vector<std::string> &Kept,
                    std::string &Error) override {
    if (!Kept.empty() && TestNamedMDs(Kept))
      return KeepSuffix;
    if (!Prefix.empty() && TestNamedMDs(Prefix))
      return KeepPrefix;
    return NoFailure;
  }

  bool TestNamedMDs(std::vector<std::string> &NamedMDs);
};
}

bool ReduceCrashingNamedMD::TestNamedMDs(std::vector<std::string> &NamedMDs) {

  ValueToValueMapTy VMap;
  Module *M = CloneModule(BD.getProgram(), VMap).release();

  outs() << "Checking for crash with only these named metadata nodes:";
  unsigned NumPrint = std::min<size_t>(NamedMDs.size(), 10);
  for (unsigned i = 0, e = NumPrint; i != e; ++i)
    outs() << " " << NamedMDs[i];
  if (NumPrint < NamedMDs.size())
    outs() << "... <" << NamedMDs.size() << " total>";
  outs() << ": ";

  // Make a StringMap for faster lookup
  StringSet<> Names;
  for (const std::string &Name : NamedMDs)
    Names.insert(Name);

  // First collect all the metadata to delete in a vector, then
  // delete them all at once to avoid invalidating the iterator
  std::vector<NamedMDNode *> ToDelete;
  ToDelete.reserve(M->named_metadata_size() - Names.size());
  for (auto &NamedMD : M->named_metadata())
    if (!Names.count(NamedMD.getName()))
      ToDelete.push_back(&NamedMD);

  for (auto *NamedMD : ToDelete)
    NamedMD->eraseFromParent();

  // Verify that this is still valid.
  legacy::PassManager Passes;
  Passes.add(createVerifierPass());
  Passes.run(*M);

  // Try running on the hacked up program...
  if (TestFn(BD, M)) {
    BD.setNewProgram(M); // It crashed, keep the trimmed version...
    return true;
  }
  delete M; // It didn't crash, try something else.
  return false;
}

namespace {
// Reduce the list of operands to named metadata nodes
class ReduceCrashingNamedMDOps : public ListReducer<const MDNode *> {
  BugDriver &BD;
  bool (*TestFn)(const BugDriver &, Module *);

public:
  ReduceCrashingNamedMDOps(BugDriver &bd,
                           bool (*testFn)(const BugDriver &, Module *))
      : BD(bd), TestFn(testFn) {}

  TestResult doTest(std::vector<const MDNode *> &Prefix,
                    std::vector<const MDNode *> &Kept,
                    std::string &Error) override {
    if (!Kept.empty() && TestNamedMDOps(Kept))
      return KeepSuffix;
    if (!Prefix.empty() && TestNamedMDOps(Prefix))
      return KeepPrefix;
    return NoFailure;
  }

  bool TestNamedMDOps(std::vector<const MDNode *> &NamedMDOps);
};
}

bool ReduceCrashingNamedMDOps::TestNamedMDOps(
    std::vector<const MDNode *> &NamedMDOps) {
  // Convert list to set for fast lookup...
  SmallPtrSet<const MDNode *, 64> OldMDNodeOps;
  for (unsigned i = 0, e = NamedMDOps.size(); i != e; ++i) {
    OldMDNodeOps.insert(NamedMDOps[i]);
  }

  outs() << "Checking for crash with only " << OldMDNodeOps.size();
  if (OldMDNodeOps.size() == 1)
    outs() << " named metadata operand: ";
  else
    outs() << " named metadata operands: ";

  ValueToValueMapTy VMap;
  Module *M = CloneModule(BD.getProgram(), VMap).release();

  // This is a little wasteful. In the future it might be good if we could have
  // these dropped during cloning.
  for (auto &NamedMD : BD.getProgram()->named_metadata()) {
    // Drop the old one and create a new one
    M->eraseNamedMetadata(M->getNamedMetadata(NamedMD.getName()));
    NamedMDNode *NewNamedMDNode =
        M->getOrInsertNamedMetadata(NamedMD.getName());
    for (MDNode *op : NamedMD.operands())
      if (OldMDNodeOps.count(op))
        NewNamedMDNode->addOperand(cast<MDNode>(MapMetadata(op, VMap)));
  }

  // Verify that this is still valid.
  legacy::PassManager Passes;
  Passes.add(createVerifierPass());
  Passes.run(*M);

  // Try running on the hacked up program...
  if (TestFn(BD, M)) {
    // Make sure to use instruction pointers that point into the now-current
    // module, and that they don't include any deleted blocks.
    NamedMDOps.clear();
    for (const MDNode *Node : OldMDNodeOps)
      NamedMDOps.push_back(cast<MDNode>(VMap.MD()[Node].get()));

    BD.setNewProgram(M); // It crashed, keep the trimmed version...
    return true;
  }
  delete M; // It didn't crash, try something else.
  return false;
}

/// DebugACrash - Given a predicate that determines whether a component crashes
/// on a program, try to destructively reduce the program while still keeping
/// the predicate true.
static bool DebugACrash(BugDriver &BD,
                        bool (*TestFn)(const BugDriver &, Module *),
                        std::string &Error) {
  // See if we can get away with nuking some of the global variable initializers
  // in the program...
  if (!NoGlobalRM &&
      BD.getProgram()->global_begin() != BD.getProgram()->global_end()) {
    // Now try to reduce the number of global variable initializers in the
    // module to something small.
    Module *M = CloneModule(BD.getProgram()).release();
    bool DeletedInit = false;

    for (Module::global_iterator I = M->global_begin(), E = M->global_end();
         I != E; ++I)
      if (I->hasInitializer()) {
        DeleteGlobalInitializer(&*I);
        I->setLinkage(GlobalValue::ExternalLinkage);
        DeletedInit = true;
      }

    if (!DeletedInit) {
      delete M;  // No change made...
    } else {
      // See if the program still causes a crash...
      outs() << "\nChecking to see if we can delete global inits: ";

      if (TestFn(BD, M)) {      // Still crashes?
        BD.setNewProgram(M);
        outs() << "\n*** Able to remove all global initializers!\n";
      } else {                  // No longer crashes?
        outs() << "  - Removing all global inits hides problem!\n";
        delete M;

        std::vector<GlobalVariable*> GVs;

        for (Module::global_iterator I = BD.getProgram()->global_begin(),
               E = BD.getProgram()->global_end(); I != E; ++I)
          if (I->hasInitializer())
            GVs.push_back(&*I);

        if (GVs.size() > 1 && !BugpointIsInterrupted) {
          outs() << "\n*** Attempting to reduce the number of global "
                    << "variables in the testcase\n";

          unsigned OldSize = GVs.size();
          ReduceCrashingGlobalVariables(BD, TestFn).reduceList(GVs, Error);
          if (!Error.empty())
            return true;

          if (GVs.size() < OldSize)
            BD.EmitProgressBitcode(BD.getProgram(), "reduced-global-variables");
        }
      }
    }
  }

  // Now try to reduce the number of functions in the module to something small.
  std::vector<Function*> Functions;
  for (Function &F : *BD.getProgram())
    if (!F.isDeclaration())
      Functions.push_back(&F);

  if (Functions.size() > 1 && !BugpointIsInterrupted) {
    outs() << "\n*** Attempting to reduce the number of functions "
      "in the testcase\n";

    unsigned OldSize = Functions.size();
    ReduceCrashingFunctions(BD, TestFn).reduceList(Functions, Error);

    if (Functions.size() < OldSize)
      BD.EmitProgressBitcode(BD.getProgram(), "reduced-function");
  }

  // Attempt to delete entire basic blocks at a time to speed up
  // convergence... this actually works by setting the terminator of the blocks
  // to a return instruction then running simplifycfg, which can potentially
  // shrinks the code dramatically quickly
  //
  if (!DisableSimplifyCFG && !BugpointIsInterrupted) {
    std::vector<const BasicBlock*> Blocks;
    for (Function &F : *BD.getProgram())
      for (BasicBlock &BB : F)
        Blocks.push_back(&BB);
    unsigned OldSize = Blocks.size();
    ReduceCrashingBlocks(BD, TestFn).reduceList(Blocks, Error);
    if (Blocks.size() < OldSize)
      BD.EmitProgressBitcode(BD.getProgram(), "reduced-blocks");
  }

  // Attempt to delete instructions using bisection. This should help out nasty
  // cases with large basic blocks where the problem is at one end.
  if (!BugpointIsInterrupted) {
    std::vector<const Instruction*> Insts;
    for (const Function &F : *BD.getProgram())
      for (const BasicBlock &BB : F)
        for (const Instruction &I : BB)
          if (!isa<TerminatorInst>(&I))
            Insts.push_back(&I);

    ReduceCrashingInstructions(BD, TestFn).reduceList(Insts, Error);
  }

  // FIXME: This should use the list reducer to converge faster by deleting
  // larger chunks of instructions at a time!
  unsigned Simplification = 2;
  do {
    if (BugpointIsInterrupted) break;
    --Simplification;
    outs() << "\n*** Attempting to reduce testcase by deleting instruc"
           << "tions: Simplification Level #" << Simplification << '\n';

    // Now that we have deleted the functions that are unnecessary for the
    // program, try to remove instructions that are not necessary to cause the
    // crash.  To do this, we loop through all of the instructions in the
    // remaining functions, deleting them (replacing any values produced with
    // nulls), and then running ADCE and SimplifyCFG.  If the transformed input
    // still triggers failure, keep deleting until we cannot trigger failure
    // anymore.
    //
    unsigned InstructionsToSkipBeforeDeleting = 0;
  TryAgain:

    // Loop over all of the (non-terminator) instructions remaining in the
    // function, attempting to delete them.
    unsigned CurInstructionNum = 0;
    for (Module::const_iterator FI = BD.getProgram()->begin(),
           E = BD.getProgram()->end(); FI != E; ++FI)
      if (!FI->isDeclaration())
        for (Function::const_iterator BI = FI->begin(), E = FI->end(); BI != E;
             ++BI)
          for (BasicBlock::const_iterator I = BI->begin(), E = --BI->end();
               I != E; ++I, ++CurInstructionNum) {
            if (InstructionsToSkipBeforeDeleting) {
              --InstructionsToSkipBeforeDeleting;
            } else {
              if (BugpointIsInterrupted) goto ExitLoops;

              if (I->isEHPad() || I->getType()->isTokenTy())
                continue;

              outs() << "Checking instruction: " << *I;
              std::unique_ptr<Module> M =
                  BD.deleteInstructionFromProgram(&*I, Simplification);

              // Find out if the pass still crashes on this pass...
              if (TestFn(BD, M.get())) {
                // Yup, it does, we delete the old module, and continue trying
                // to reduce the testcase...
                BD.setNewProgram(M.release());
                InstructionsToSkipBeforeDeleting = CurInstructionNum;
                goto TryAgain;  // I wish I had a multi-level break here!
              }
            }
          }

    if (InstructionsToSkipBeforeDeleting) {
      InstructionsToSkipBeforeDeleting = 0;
      goto TryAgain;
    }

  } while (Simplification);

  if (!NoNamedMDRM) {
    BD.EmitProgressBitcode(BD.getProgram(), "reduced-instructions");

    if (!BugpointIsInterrupted) {
      // Try to reduce the amount of global metadata (particularly debug info),
      // by dropping global named metadata that anchors them
      outs() << "\n*** Attempting to remove named metadata: ";
      std::vector<std::string> NamedMDNames;
      for (auto &NamedMD : BD.getProgram()->named_metadata())
        NamedMDNames.push_back(NamedMD.getName().str());
      ReduceCrashingNamedMD(BD, TestFn).reduceList(NamedMDNames, Error);
    }

    if (!BugpointIsInterrupted) {
      // Now that we quickly dropped all the named metadata that doesn't
      // contribute to the crash, bisect the operands of the remaining ones
      std::vector<const MDNode *> NamedMDOps;
      for (auto &NamedMD : BD.getProgram()->named_metadata())
        for (auto op : NamedMD.operands())
          NamedMDOps.push_back(op);
      ReduceCrashingNamedMDOps(BD, TestFn).reduceList(NamedMDOps, Error);
    }
  }

ExitLoops:

  // Try to clean up the testcase by running funcresolve and globaldce...
  if (!BugpointIsInterrupted) {
    outs() << "\n*** Attempting to perform final cleanups: ";
    Module *M = CloneModule(BD.getProgram()).release();
    M = BD.performFinalCleanups(M, true).release();

    // Find out if the pass still crashes on the cleaned up program...
    if (TestFn(BD, M)) {
      BD.setNewProgram(M);     // Yup, it does, keep the reduced version...
    } else {
      delete M;
    }
  }

  BD.EmitProgressBitcode(BD.getProgram(), "reduced-simplified");

  return false;
}

static bool TestForOptimizerCrash(const BugDriver &BD, Module *M) {
  return BD.runPasses(M);
}

/// debugOptimizerCrash - This method is called when some pass crashes on input.
/// It attempts to prune down the testcase to something reasonable, and figure
/// out exactly which pass is crashing.
///
bool BugDriver::debugOptimizerCrash(const std::string &ID) {
  outs() << "\n*** Debugging optimizer crash!\n";

  std::string Error;
  // Reduce the list of passes which causes the optimizer to crash...
  if (!BugpointIsInterrupted && !DontReducePassList)
    ReducePassList(*this).reduceList(PassesToRun, Error);
  assert(Error.empty());

  outs() << "\n*** Found crashing pass"
         << (PassesToRun.size() == 1 ? ": " : "es: ")
         << getPassesString(PassesToRun) << '\n';

  EmitProgressBitcode(Program, ID);

  bool Success = DebugACrash(*this, TestForOptimizerCrash, Error);
  assert(Error.empty());
  return Success;
}

static bool TestForCodeGenCrash(const BugDriver &BD, Module *M) {
  std::string Error;
  BD.compileProgram(M, &Error);
  if (!Error.empty()) {
    errs() << "<crash>\n";
    return true;  // Tool is still crashing.
  }
  errs() << '\n';
  return false;
}

/// debugCodeGeneratorCrash - This method is called when the code generator
/// crashes on an input.  It attempts to reduce the input as much as possible
/// while still causing the code generator to crash.
bool BugDriver::debugCodeGeneratorCrash(std::string &Error) {
  errs() << "*** Debugging code generator crash!\n";

  return DebugACrash(*this, TestForCodeGenCrash, Error);
}