llvm/lib/Transforms/Utils/Debugify.cpp

//===- Debugify.cpp - Attach synthetic debug info to everything -----------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// \file This pass attaches synthetic debug info to everything. It can be used
/// to create targeted tests for debug info preservation.
///
//===----------------------------------------------------------------------===//

#include "llvm/Transforms/Utils/Debugify.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/IR/DIBuilder.h"
#include "llvm/IR/DebugInfo.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"

using namespace llvm;

namespace {

cl::opt<bool> Quiet("debugify-quiet",
                    cl::desc("Suppress verbose debugify output"));

enum class Level {
  Locations,
  LocationsAndVariables
};
cl::opt<Level> DebugifyLevel(
    "debugify-level", cl::desc("Kind of debug info to add"),
    cl::values(clEnumValN(Level::Locations, "locations", "Locations only"),
               clEnumValN(Level::LocationsAndVariables, "location+variables",
                          "Locations and Variables")),
    cl::init(Level::LocationsAndVariables));

raw_ostream &dbg() { return Quiet ? nulls() : errs(); }

uint64_t getAllocSizeInBits(Module &M, Type *Ty) {
  return Ty->isSized() ? M.getDataLayout().getTypeAllocSizeInBits(Ty) : 0;
}

bool isFunctionSkipped(Function &F) {
  return F.isDeclaration() || !F.hasExactDefinition();
}

/// Find the basic block's terminating instruction.
///
/// Special care is needed to handle musttail and deopt calls, as these behave
/// like (but are in fact not) terminators.
Instruction *findTerminatingInstruction(BasicBlock &BB) {
  if (auto *I = BB.getTerminatingMustTailCall())
    return I;
  if (auto *I = BB.getTerminatingDeoptimizeCall())
    return I;
  return BB.getTerminator();
}
} // end anonymous namespace

bool llvm::applyDebugifyMetadata(
    Module &M, iterator_range<Module::iterator> Functions, StringRef Banner,
    std::function<bool(DIBuilder &DIB, Function &F)> ApplyToMF) {
  // Skip modules with debug info.
  if (M.getNamedMetadata("llvm.dbg.cu")) {
    dbg() << Banner << "Skipping module with debug info\n";
    return false;
  }

  DIBuilder DIB(M);
  LLVMContext &Ctx = M.getContext();
  auto *Int32Ty = Type::getInt32Ty(Ctx);

  // Get a DIType which corresponds to Ty.
  DenseMap<uint64_t, DIType *> TypeCache;
  auto getCachedDIType = [&](Type *Ty) -> DIType * {
    uint64_t Size = getAllocSizeInBits(M, Ty);
    DIType *&DTy = TypeCache[Size];
    if (!DTy) {
      std::string Name = "ty" + utostr(Size);
      DTy = DIB.createBasicType(Name, Size, dwarf::DW_ATE_unsigned);
    }
    return DTy;
  };

  unsigned NextLine = 1;
  unsigned NextVar = 1;
  auto File = DIB.createFile(M.getName(), "/");
  auto CU = DIB.createCompileUnit(dwarf::DW_LANG_C, File, "debugify",
                                  /*isOptimized=*/true, "", 0);

  // Visit each instruction.
  for (Function &F : Functions) {
    if (isFunctionSkipped(F))
      continue;

    bool InsertedDbgVal = false;
    auto SPType = DIB.createSubroutineType(DIB.getOrCreateTypeArray(None));
    DISubprogram::DISPFlags SPFlags =
        DISubprogram::SPFlagDefinition | DISubprogram::SPFlagOptimized;
    if (F.hasPrivateLinkage() || F.hasInternalLinkage())
      SPFlags |= DISubprogram::SPFlagLocalToUnit;
    auto SP = DIB.createFunction(CU, F.getName(), F.getName(), File, NextLine,
                                 SPType, NextLine, DINode::FlagZero, SPFlags);
    F.setSubprogram(SP);

    // Helper that inserts a dbg.value before \p InsertBefore, copying the
    // location (and possibly the type, if it's non-void) from \p TemplateInst.
    auto insertDbgVal = [&](Instruction &TemplateInst,
                            Instruction *InsertBefore) {
      std::string Name = utostr(NextVar++);
      Value *V = &TemplateInst;
      if (TemplateInst.getType()->isVoidTy())
        V = ConstantInt::get(Int32Ty, 0);
      const DILocation *Loc = TemplateInst.getDebugLoc().get();
      auto LocalVar = DIB.createAutoVariable(SP, Name, File, Loc->getLine(),
                                             getCachedDIType(V->getType()),
                                             /*AlwaysPreserve=*/true);
      DIB.insertDbgValueIntrinsic(V, LocalVar, DIB.createExpression(), Loc,
                                  InsertBefore);
    };

    for (BasicBlock &BB : F) {
      // Attach debug locations.
      for (Instruction &I : BB)
        I.setDebugLoc(DILocation::get(Ctx, NextLine++, 1, SP));

      if (DebugifyLevel < Level::LocationsAndVariables)
        continue;

      // Inserting debug values into EH pads can break IR invariants.
      if (BB.isEHPad())
        continue;

      // Find the terminating instruction, after which no debug values are
      // attached.
      Instruction *LastInst = findTerminatingInstruction(BB);
      assert(LastInst && "Expected basic block with a terminator");

      // Maintain an insertion point which can't be invalidated when updates
      // are made.
      BasicBlock::iterator InsertPt = BB.getFirstInsertionPt();
      assert(InsertPt != BB.end() && "Expected to find an insertion point");
      Instruction *InsertBefore = &*InsertPt;

      // Attach debug values.
      for (Instruction *I = &*BB.begin(); I != LastInst; I = I->getNextNode()) {
        // Skip void-valued instructions.
        if (I->getType()->isVoidTy())
          continue;

        // Phis and EH pads must be grouped at the beginning of the block.
        // Only advance the insertion point when we finish visiting these.
        if (!isa<PHINode>(I) && !I->isEHPad())
          InsertBefore = I->getNextNode();

        insertDbgVal(*I, InsertBefore);
        InsertedDbgVal = true;
      }
    }
    // Make sure we emit at least one dbg.value, otherwise MachineDebugify may
    // not have anything to work with as it goes about inserting DBG_VALUEs.
    // (It's common for MIR tests to be written containing skeletal IR with
    // empty functions -- we're still interested in debugifying the MIR within
    // those tests, and this helps with that.)
    if (DebugifyLevel == Level::LocationsAndVariables && !InsertedDbgVal) {
      auto *Term = findTerminatingInstruction(F.getEntryBlock());
      insertDbgVal(*Term, Term);
    }
    if (ApplyToMF)
      ApplyToMF(DIB, F);
    DIB.finalizeSubprogram(SP);
  }
  DIB.finalize();

  // Track the number of distinct lines and variables.
  NamedMDNode *NMD = M.getOrInsertNamedMetadata("llvm.debugify");
  auto addDebugifyOperand = [&](unsigned N) {
    NMD->addOperand(MDNode::get(
        Ctx, ValueAsMetadata::getConstant(ConstantInt::get(Int32Ty, N))));
  };
  addDebugifyOperand(NextLine - 1); // Original number of lines.
  addDebugifyOperand(NextVar - 1);  // Original number of variables.
  assert(NMD->getNumOperands() == 2 &&
         "llvm.debugify should have exactly 2 operands!");

  // Claim that this synthetic debug info is valid.
  StringRef DIVersionKey = "Debug Info Version";
  if (!M.getModuleFlag(DIVersionKey))
    M.addModuleFlag(Module::Warning, DIVersionKey, DEBUG_METADATA_VERSION);

  return true;
}

bool llvm::stripDebugifyMetadata(Module &M) {
  bool Changed = false;

  // Remove the llvm.debugify module-level named metadata.
  NamedMDNode *DebugifyMD = M.getNamedMetadata("llvm.debugify");
  if (DebugifyMD) {
    M.eraseNamedMetadata(DebugifyMD);
    Changed = true;
  }

  // Strip out all debug intrinsics and supporting metadata (subprograms, types,
  // variables, etc).
  Changed |= StripDebugInfo(M);

  // Strip out the dead dbg.value prototype.
  Function *DbgValF = M.getFunction("llvm.dbg.value");
  if (DbgValF) {
    assert(DbgValF->isDeclaration() && DbgValF->use_empty() &&
           "Not all debug info stripped?");
    DbgValF->eraseFromParent();
    Changed = true;
  }

  // Strip out the module-level Debug Info Version metadata.
  // FIXME: There must be an easier way to remove an operand from a NamedMDNode.
  NamedMDNode *NMD = M.getModuleFlagsMetadata();
  if (!NMD)
    return Changed;
  SmallVector<MDNode *, 4> Flags;
  for (MDNode *Flag : NMD->operands())
    Flags.push_back(Flag);
  NMD->clearOperands();
  for (MDNode *Flag : Flags) {
    MDString *Key = dyn_cast_or_null<MDString>(Flag->getOperand(1));
    if (Key->getString() == "Debug Info Version") {
      Changed = true;
      continue;
    }
    NMD->addOperand(Flag);
  }
  // If we left it empty we might as well remove it.
  if (NMD->getNumOperands() == 0)
    NMD->eraseFromParent();

  return Changed;
}

namespace {
/// Return true if a mis-sized diagnostic is issued for \p DVI.
bool diagnoseMisSizedDbgValue(Module &M, DbgValueInst *DVI) {
  // The size of a dbg.value's value operand should match the size of the
  // variable it corresponds to.
  //
  // TODO: This, along with a check for non-null value operands, should be
  // promoted to verifier failures.
  Value *V = DVI->getValue();
  if (!V)
    return false;

  // For now, don't try to interpret anything more complicated than an empty
  // DIExpression. Eventually we should try to handle OP_deref and fragments.
  if (DVI->getExpression()->getNumElements())
    return false;

  Type *Ty = V->getType();
  uint64_t ValueOperandSize = getAllocSizeInBits(M, Ty);
  Optional<uint64_t> DbgVarSize = DVI->getFragmentSizeInBits();
  if (!ValueOperandSize || !DbgVarSize)
    return false;

  bool HasBadSize = false;
  if (Ty->isIntegerTy()) {
    auto Signedness = DVI->getVariable()->getSignedness();
    if (Signedness && *Signedness == DIBasicType::Signedness::Signed)
      HasBadSize = ValueOperandSize < *DbgVarSize;
  } else {
    HasBadSize = ValueOperandSize != *DbgVarSize;
  }

  if (HasBadSize) {
    dbg() << "ERROR: dbg.value operand has size " << ValueOperandSize
          << ", but its variable has size " << *DbgVarSize << ": ";
    DVI->print(dbg());
    dbg() << "\n";
  }
  return HasBadSize;
}

bool checkDebugifyMetadata(Module &M,
                           iterator_range<Module::iterator> Functions,
                           StringRef NameOfWrappedPass, StringRef Banner,
                           bool Strip, DebugifyStatsMap *StatsMap) {
  // Skip modules without debugify metadata.
  NamedMDNode *NMD = M.getNamedMetadata("llvm.debugify");
  if (!NMD) {
    dbg() << Banner << ": Skipping module without debugify metadata\n";
    return false;
  }

  auto getDebugifyOperand = [&](unsigned Idx) -> unsigned {
    return mdconst::extract<ConstantInt>(NMD->getOperand(Idx)->getOperand(0))
        ->getZExtValue();
  };
  assert(NMD->getNumOperands() == 2 &&
         "llvm.debugify should have exactly 2 operands!");
  unsigned OriginalNumLines = getDebugifyOperand(0);
  unsigned OriginalNumVars = getDebugifyOperand(1);
  bool HasErrors = false;

  // Track debug info loss statistics if able.
  DebugifyStatistics *Stats = nullptr;
  if (StatsMap && !NameOfWrappedPass.empty())
    Stats = &StatsMap->operator[](NameOfWrappedPass);

  BitVector MissingLines{OriginalNumLines, true};
  BitVector MissingVars{OriginalNumVars, true};
  for (Function &F : Functions) {
    if (isFunctionSkipped(F))
      continue;

    // Find missing lines.
    for (Instruction &I : instructions(F)) {
      if (isa<DbgValueInst>(&I) || isa<PHINode>(&I))
        continue;

      auto DL = I.getDebugLoc();
      if (DL && DL.getLine() != 0) {
        MissingLines.reset(DL.getLine() - 1);
        continue;
      }

      if (!DL) {
        dbg() << "WARNING: Instruction with empty DebugLoc in function ";
        dbg() << F.getName() << " --";
        I.print(dbg());
        dbg() << "\n";
      }
    }

    // Find missing variables and mis-sized debug values.
    for (Instruction &I : instructions(F)) {
      auto *DVI = dyn_cast<DbgValueInst>(&I);
      if (!DVI)
        continue;

      unsigned Var = ~0U;
      (void)to_integer(DVI->getVariable()->getName(), Var, 10);
      assert(Var <= OriginalNumVars && "Unexpected name for DILocalVariable");
      bool HasBadSize = diagnoseMisSizedDbgValue(M, DVI);
      if (!HasBadSize)
        MissingVars.reset(Var - 1);
      HasErrors |= HasBadSize;
    }
  }

  // Print the results.
  for (unsigned Idx : MissingLines.set_bits())
    dbg() << "WARNING: Missing line " << Idx + 1 << "\n";

  for (unsigned Idx : MissingVars.set_bits())
    dbg() << "WARNING: Missing variable " << Idx + 1 << "\n";

  // Update DI loss statistics.
  if (Stats) {
    Stats->NumDbgLocsExpected += OriginalNumLines;
    Stats->NumDbgLocsMissing += MissingLines.count();
    Stats->NumDbgValuesExpected += OriginalNumVars;
    Stats->NumDbgValuesMissing += MissingVars.count();
  }

  dbg() << Banner;
  if (!NameOfWrappedPass.empty())
    dbg() << " [" << NameOfWrappedPass << "]";
  dbg() << ": " << (HasErrors ? "FAIL" : "PASS") << '\n';

  // Strip debugify metadata if required.
  if (Strip)
    return stripDebugifyMetadata(M);

  return false;
}

/// ModulePass for attaching synthetic debug info to everything, used with the
/// legacy module pass manager.
struct DebugifyModulePass : public ModulePass {
  bool runOnModule(Module &M) override {
    return applyDebugifyMetadata(M, M.functions(),
                                 "ModuleDebugify: ", /*ApplyToMF*/ nullptr);
  }

  DebugifyModulePass() : ModulePass(ID) {}

  void getAnalysisUsage(AnalysisUsage &AU) const override {
    AU.setPreservesAll();
  }

  static char ID; // Pass identification.
};

/// FunctionPass for attaching synthetic debug info to instructions within a
/// single function, used with the legacy module pass manager.
struct DebugifyFunctionPass : public FunctionPass {
  bool runOnFunction(Function &F) override {
    Module &M = *F.getParent();
    auto FuncIt = F.getIterator();
    return applyDebugifyMetadata(M, make_range(FuncIt, std::next(FuncIt)),
                                 "FunctionDebugify: ", /*ApplyToMF*/ nullptr);
  }

  DebugifyFunctionPass() : FunctionPass(ID) {}

  void getAnalysisUsage(AnalysisUsage &AU) const override {
    AU.setPreservesAll();
  }

  static char ID; // Pass identification.
};

/// ModulePass for checking debug info inserted by -debugify, used with the
/// legacy module pass manager.
struct CheckDebugifyModulePass : public ModulePass {
  bool runOnModule(Module &M) override {
    return checkDebugifyMetadata(M, M.functions(), NameOfWrappedPass,
                                 "CheckModuleDebugify", Strip, StatsMap);
  }

  CheckDebugifyModulePass(bool Strip = false, StringRef NameOfWrappedPass = "",
                          DebugifyStatsMap *StatsMap = nullptr)
      : ModulePass(ID), Strip(Strip), NameOfWrappedPass(NameOfWrappedPass),
        StatsMap(StatsMap) {}

  void getAnalysisUsage(AnalysisUsage &AU) const override {
    AU.setPreservesAll();
  }

  static char ID; // Pass identification.

private:
  bool Strip;
  StringRef NameOfWrappedPass;
  DebugifyStatsMap *StatsMap;
};

/// FunctionPass for checking debug info inserted by -debugify-function, used
/// with the legacy module pass manager.
struct CheckDebugifyFunctionPass : public FunctionPass {
  bool runOnFunction(Function &F) override {
    Module &M = *F.getParent();
    auto FuncIt = F.getIterator();
    return checkDebugifyMetadata(M, make_range(FuncIt, std::next(FuncIt)),
                                 NameOfWrappedPass, "CheckFunctionDebugify",
                                 Strip, StatsMap);
  }

  CheckDebugifyFunctionPass(bool Strip = false,
                            StringRef NameOfWrappedPass = "",
                            DebugifyStatsMap *StatsMap = nullptr)
      : FunctionPass(ID), Strip(Strip), NameOfWrappedPass(NameOfWrappedPass),
        StatsMap(StatsMap) {}

  void getAnalysisUsage(AnalysisUsage &AU) const override {
    AU.setPreservesAll();
  }

  static char ID; // Pass identification.

private:
  bool Strip;
  StringRef NameOfWrappedPass;
  DebugifyStatsMap *StatsMap;
};

} // end anonymous namespace

ModulePass *createDebugifyModulePass() { return new DebugifyModulePass(); }

FunctionPass *createDebugifyFunctionPass() {
  return new DebugifyFunctionPass();
}

PreservedAnalyses NewPMDebugifyPass::run(Module &M, ModuleAnalysisManager &) {
  applyDebugifyMetadata(M, M.functions(),
                        "ModuleDebugify: ", /*ApplyToMF*/ nullptr);
  return PreservedAnalyses::all();
}

ModulePass *createCheckDebugifyModulePass(bool Strip,
                                          StringRef NameOfWrappedPass,
                                          DebugifyStatsMap *StatsMap) {
  return new CheckDebugifyModulePass(Strip, NameOfWrappedPass, StatsMap);
}

FunctionPass *createCheckDebugifyFunctionPass(bool Strip,
                                              StringRef NameOfWrappedPass,
                                              DebugifyStatsMap *StatsMap) {
  return new CheckDebugifyFunctionPass(Strip, NameOfWrappedPass, StatsMap);
}

PreservedAnalyses NewPMCheckDebugifyPass::run(Module &M,
                                              ModuleAnalysisManager &) {
  checkDebugifyMetadata(M, M.functions(), "", "CheckModuleDebugify", false,
                        nullptr);
  return PreservedAnalyses::all();
}

char DebugifyModulePass::ID = 0;
static RegisterPass<DebugifyModulePass> DM("debugify",
                                           "Attach debug info to everything");

char CheckDebugifyModulePass::ID = 0;
static RegisterPass<CheckDebugifyModulePass>
    CDM("check-debugify", "Check debug info from -debugify");

char DebugifyFunctionPass::ID = 0;
static RegisterPass<DebugifyFunctionPass> DF("debugify-function",
                                             "Attach debug info to a function");

char CheckDebugifyFunctionPass::ID = 0;
static RegisterPass<CheckDebugifyFunctionPass>
    CDF("check-debugify-function", "Check debug info from -debugify-function");