[DebugLocCov] Plumbing to enable detailed and accurate tracking of DebugLocs

clang/include/clang/Basic/CodeGenOptions.h

@@ -221,6 +221,7 @@ class CodeGenOptions : public CodeGenOptionsBase {
   /// The file to use for dumping bug report by `Debugify` for original
   /// debug info.
   std::string DIBugsReportFilePath;
+  std::string DIBugsReportArgString;
 
   /// The floating-point denormal mode to use.
   llvm::DenormalMode FPDenormalMode = llvm::DenormalMode::getIEEE();

clang/lib/CodeGen/BackendUtil.cpp

@@ -904,13 +904,43 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
   DebugifyEachInstrumentation Debugify;
   DebugInfoPerPass DebugInfoBeforePass;
   if (CodeGenOpts.EnableDIPreservationVerify) {
+
     Debugify.setDebugifyMode(DebugifyMode::OriginalDebugInfo);
     Debugify.setDebugInfoBeforePass(DebugInfoBeforePass);
 
-    if (!CodeGenOpts.DIBugsReportFilePath.empty())
+    if (!CodeGenOpts.DIBugsReportFilePath.empty()) {
       Debugify.setOrigDIVerifyBugsReportFilePath(
           CodeGenOpts.DIBugsReportFilePath);
+      std::error_code EC;
+      raw_fd_ostream OS_FILE{CodeGenOpts.DIBugsReportFilePath, EC,
+                    sys::fs::OF_Append | sys::fs::OF_TextWithCRLF};
+      if (EC) {
+        errs() << "Could not open file: " << EC.message() << ", "
+              << CodeGenOpts.DIBugsReportFilePath << '\n';
+      } else {
+        if (auto L = OS_FILE.lock()) {
+          OS_FILE << CodeGenOpts.DIBugsReportArgString;
+        }
+        OS_FILE.close();
+      }
+    }
     Debugify.registerCallbacks(PIC, MAM);
+
+#ifdef LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING
+    // If we're using debug location coverage tracking, mark all the
+    // instructions coming out of the frontend without a DebugLoc as being
+    // intentional line-zero locations, to prevent both those instructions and
+    // new instructions that inherit their location from being treated as
+    // incorrectly empty locations.
+    for (Function &F : *TheModule) {
+      if (!F.getSubprogram())
+        continue;
+      for (BasicBlock &BB : F)
+        for (Instruction &I : BB)
+          if (!I.getDebugLoc())
+            I.setDebugLoc(DebugLoc::getLineZero());
+    }
+#endif
   }
   // Attempt to load pass plugins and register their callbacks with PB.
   for (auto &PluginFN : CodeGenOpts.PassPlugins) {

clang/lib/Frontend/CompilerInvocation.cpp

@@ -1876,6 +1876,16 @@ bool CompilerInvocation::ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args,
         << Opts.DIBugsReportFilePath;
     Opts.DIBugsReportFilePath = "";
   }
+  if (Opts.EnableDIPreservationVerify && Opts.DIBugsReportFilePath.size()) {
+    std::string ArgString;
+    llvm::raw_string_ostream OS(ArgString);
+    OS << "{\"file\":\"" << OutputFile << "\", \"args\":\"";
+    for (Arg *A : Args) {
+      OS << A->getAsString(Args) << " ";
+    }
+    OS << "\"}\n";
+    Opts.DIBugsReportArgString = ArgString;
+  }
 
   Opts.NewStructPathTBAA = !Args.hasArg(OPT_no_struct_path_tbaa) &&
                            Args.hasArg(OPT_new_struct_path_tbaa);

llvm/CMakeLists.txt

@@ -524,6 +524,8 @@ endif()
 
 option(LLVM_ENABLE_CRASH_DUMPS "Turn on memory dumps on crashes. Currently only implemented on Windows." OFF)
 
+option(LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING "Enhance debugify's line number tracking at the cost of performance; abi-breaking." ON)
+
 set(WINDOWS_PREFER_FORWARD_SLASH_DEFAULT OFF)
 if (MINGW)
   # Cygwin doesn't identify itself as Windows, and thus gets path::Style::posix

llvm/include/llvm/CodeGen/GlobalISel/LegalizationArtifactCombiner.h

@@ -100,8 +100,8 @@ class LegalizationArtifactCombiner {
       const LLT DstTy = MRI.getType(DstReg);
       if (isInstLegal({TargetOpcode::G_CONSTANT, {DstTy}})) {
         auto &CstVal = SrcMI->getOperand(1);
-        auto *MergedLocation = DILocation::getMergedLocation(
-            MI.getDebugLoc().get(), SrcMI->getDebugLoc().get());
+        auto MergedLocation = DebugLoc::getMergedLocation(
+            MI.getDebugLoc(), SrcMI->getDebugLoc());
         // Set the debug location to the merged location of the SrcMI and the MI
         // if the aext fold is successful.
         Builder.setDebugLoc(MergedLocation);

llvm/include/llvm/Config/config.h.cmake

@@ -19,6 +19,10 @@
 /* Define to 1 to enable crash memory dumps, and to 0 otherwise. */
 #cmakedefine01 LLVM_ENABLE_CRASH_DUMPS
 
+/* Define to 1 to enable expensive checks for debug location coverage checking,
+   and to 0 otherwise. */
+#cmakedefine01 LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING
+
 /* Define to 1 to prefer forward slashes on Windows, and to 0 prefer
    backslashes. */
 #cmakedefine01 LLVM_WINDOWS_PREFER_FORWARD_SLASH

llvm/include/llvm/IR/DebugLoc.h

@@ -14,6 +14,7 @@
 #ifndef LLVM_IR_DEBUGLOC_H
 #define LLVM_IR_DEBUGLOC_H
 
+#include "llvm/Config/config.h"
 #include "llvm/IR/TrackingMDRef.h"
 #include "llvm/Support/DataTypes.h"
 
@@ -22,6 +23,74 @@ namespace llvm {
   class LLVMContext;
   class raw_ostream;
   class DILocation;
+  class Function;
+
+#ifdef LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING
+  struct DbgLocOriginBacktrace {
+    static constexpr unsigned long MaxDepth = 16;
+    SmallVector<std::pair<int, std::array<void *, MaxDepth>>, 0> Stacktraces;
+    DbgLocOriginBacktrace(bool ShouldCollectTrace);
+    void addTrace();
+  };
+
+  // Used to represent different "kinds" of DebugLoc, expressing that a DebugLoc
+  // is either ordinary, containing a valid DILocation, or otherwise describing
+  // the reason why the DebugLoc does not contain a valid DILocation.
+  enum class DebugLocKind : uint8_t {
+    // DebugLoc should contain a valid DILocation.
+    Normal,
+    // DebugLoc intentionally does not have a valid DILocation; may be for a
+    // compiler-generated instruction, or an explicitly dropped location.
+    LineZero,
+    // DebugLoc does not have a known or currently knowable source location.
+    Unknown,
+    // Used for instructions that we don't expect to be emitted, and so can omit
+    // a valid DILocation. It is an error to try and emit a Temporary DebugLoc
+    // into the line table.
+    Temporary
+  };
+
+  // Extends TrackingMDNodeRef to also store a DebugLocKind and Backtrace,
+  // allowing Debugify to ignore intentionally-empty DebugLocs and display the
+  // code responsible for generating unintentionally-empty DebugLocs.
+  class DILocAndCoverageTracking : public TrackingMDNodeRef {
+  public:
+    DebugLocKind Kind;
+    // Currently we only need to track the Origin of this DILoc when using a
+    // normal empty DebugLoc, so only collect the stack trace in those cases.
+    DbgLocOriginBacktrace Origin;
+    DILocAndCoverageTracking(bool NeedsStacktrace = true)
+        : TrackingMDNodeRef(nullptr), Kind(DebugLocKind::Normal), Origin(NeedsStacktrace) {
+    }
+    // Valid or nullptr MDNode*, normal DebugLocKind
+    DILocAndCoverageTracking(const MDNode *Loc)
+        : TrackingMDNodeRef(const_cast<MDNode *>(Loc)),
+          Kind(DebugLocKind::Normal), Origin(!Loc) {}
+    DILocAndCoverageTracking(const DILocation *Loc);
+    // Always nullptr MDNode*, any DebugLocKind
+    DILocAndCoverageTracking(DebugLocKind Kind)
+        : TrackingMDNodeRef(nullptr), Kind(Kind),
+          Origin(Kind == DebugLocKind::Normal) {}
+  };
+  template <> struct simplify_type<DILocAndCoverageTracking> {
+    using SimpleType = MDNode *;
+
+    static MDNode *getSimplifiedValue(DILocAndCoverageTracking &MD) {
+      return MD.get();
+    }
+  };
+  template <> struct simplify_type<const DILocAndCoverageTracking> {
+    using SimpleType = MDNode *;
+
+    static MDNode *getSimplifiedValue(const DILocAndCoverageTracking &MD) {
+      return MD.get();
+    }
+  };
+
+  using DebugLocTrackingRef = DILocAndCoverageTracking;
+#else
+  using DebugLocTrackingRef = TrackingMDNodeRef;
+#endif // LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING
 
   /// A debug info location.
   ///
@@ -31,7 +100,8 @@ namespace llvm {
   /// To avoid extra includes, \a DebugLoc doubles the \a DILocation API with a
   /// one based on relatively opaque \a MDNode pointers.
   class DebugLoc {
-    TrackingMDNodeRef Loc;
+
+    DebugLocTrackingRef Loc;
 
   public:
     DebugLoc() = default;
@@ -47,6 +117,28 @@ namespace llvm {
     /// IR.
     explicit DebugLoc(const MDNode *N);
 
+#ifdef LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING
+    DebugLoc(DebugLocKind Kind) : Loc(Kind) {}
+    DebugLocKind getKind() const { return Loc.Kind; }
+    DbgLocOriginBacktrace getOrigin() const { return Loc.Origin; }
+    DebugLoc getCopied() const {
+      DebugLoc NewDL = *this;
+      NewDL.Loc.Origin.addTrace();
+      return NewDL;
+    }
+#else
+    DebugLoc getCopied() const {
+      return *this;
+    }
+#endif
+
+    static DebugLoc getTemporary();
+    static DebugLoc getUnknown();
+    static DebugLoc getLineZero();
+
+    static DebugLoc getMergedLocations(ArrayRef<DebugLoc> Locs);
+    static DebugLoc getMergedLocation(DebugLoc LocA, DebugLoc LocB);
+
     /// Get the underlying \a DILocation.
     ///
     /// \pre !*this or \c isa<DILocation>(getAsMDNode()).

llvm/include/llvm/IR/IRBuilder.h

@@ -93,9 +93,15 @@ class IRBuilderBase {
   /// created instructions, like !dbg metadata.
   SmallVector<std::pair<unsigned, MDNode *>, 2> MetadataToCopy;
 
+  DebugLoc StoredDL;
+
   /// Add or update the an entry (Kind, MD) to MetadataToCopy, if \p MD is not
   /// null. If \p MD is null, remove the entry with \p Kind.
   void AddOrRemoveMetadataToCopy(unsigned Kind, MDNode *MD) {
+    if (Kind == LLVMContext::MD_dbg) {
+      StoredDL = DebugLoc(MD);
+    }
+
     if (!MD) {
       erase_if(MetadataToCopy, [Kind](const std::pair<unsigned, MDNode *> &KV) {
         return KV.first == Kind;
@@ -216,6 +222,10 @@ class IRBuilderBase {
   /// Set location information used by debugging information.
   void SetCurrentDebugLocation(DebugLoc L) {
     AddOrRemoveMetadataToCopy(LLVMContext::MD_dbg, L.getAsMDNode());
+    // Although we set StoredDL in the above call, we prefer to use the exact
+    // DebugLoc we were given, so overwrite it here; the call is only needed to
+    // update the entry in MetadataToCopy.
+    StoredDL = std::move(L);
   }
 
   /// Set nosanitize metadata.
@@ -229,8 +239,11 @@ class IRBuilderBase {
   /// not on \p Src will be dropped from MetadataToCopy.
   void CollectMetadataToCopy(Instruction *Src,
                              ArrayRef<unsigned> MetadataKinds) {
-    for (unsigned K : MetadataKinds)
+    for (unsigned K : MetadataKinds) {
       AddOrRemoveMetadataToCopy(K, Src->getMetadata(K));
+      if (K == LLVMContext::MD_dbg)
+        SetCurrentDebugLocation(Src->getDebugLoc());
+    }
   }
 
   /// Get location information used by debugging information.
@@ -242,8 +255,21 @@ class IRBuilderBase {
 
   /// Add all entries in MetadataToCopy to \p I.
   void AddMetadataToInst(Instruction *I) const {
-    for (const auto &KV : MetadataToCopy)
+    for (const auto &KV : MetadataToCopy) {
+      if (KV.first == LLVMContext::MD_dbg) {
+        // If `!I->getDebugLoc()` then we will call this below anyway, so skip
+        // a duplicate call here.
+        if (I->getDebugLoc())
+          I->setDebugLoc(StoredDL.getCopied());
+        continue;
+      }
       I->setMetadata(KV.first, KV.second);
+    }
+    // If I does not have an existing DebugLoc and no DebugLoc has been set
+    // here, we copy our DebugLoc to I anyway, because more likely than not I
+    // is a new instruction whose DL should originate from this builder.
+    if (!I->getDebugLoc())
+      I->setDebugLoc(StoredDL.getCopied());
   }
 
   /// Get the return type of the current function that we're emitting

llvm/include/llvm/IR/Instruction.h

@@ -647,6 +647,7 @@ class Instruction : public User,
   /// The DebugLoc attached to this instruction will be overwritten by the
   /// merged DebugLoc.
   void applyMergedLocation(DILocation *LocA, DILocation *LocB);
+  void applyMergedLocation(DebugLoc LocA, DebugLoc LocB);
 
   /// Updates the debug location given that the instruction has been hoisted
   /// from a block to a predecessor of that block.

llvm/include/llvm/Support/Signals.h

@@ -14,13 +14,29 @@
 #ifndef LLVM_SUPPORT_SIGNALS_H
 #define LLVM_SUPPORT_SIGNALS_H
 
+#include "llvm/Config/config.h"
+#include <array>
 #include <cstdint>
 #include <string>
 
 namespace llvm {
 class StringRef;
 class raw_ostream;
 
+#ifdef LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING
+template <typename T, typename Enable> struct DenseMapInfo;
+template <typename ValueT, typename ValueInfoT> class DenseSet;
+namespace detail {
+template <typename KeyT, typename ValueT> struct DenseMapPair;
+}
+template <typename KeyT, typename ValueT, typename KeyInfoT, typename BucketT>
+class DenseMap;
+using AddressSet = DenseSet<void *, DenseMapInfo<void *, void>>;
+using SymbolizedAddressMap =
+    DenseMap<void *, std::string, DenseMapInfo<void *, void>,
+             detail::DenseMapPair<void *, std::string>>;
+#endif
+
 namespace sys {
 
   /// This function runs all the registered interrupt handlers, including the
@@ -55,6 +71,15 @@ namespace sys {
   ///        specified, the entire frame is printed.
   void PrintStackTrace(raw_ostream &OS, int Depth = 0);
 
+#ifdef LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING
+  template <unsigned long MaxDepth> int getStackTrace(std::array<void *, MaxDepth> &StackTrace);
+
+  /// Takes a set of \p Addresses, symbolizes them and stores the result in the
+  /// provided \p SymbolizedAddresses map.
+  void symbolizeAddresses(AddressSet &Addresses,
+                          SymbolizedAddressMap &SymbolizedAddresses);
+#endif
+
   // Run all registered signal handlers.
   void RunSignalHandlers();
 

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -31,6 +31,7 @@
 #include "llvm/CodeGen/TargetLowering.h"
 #include "llvm/CodeGen/TargetRegisterInfo.h"
 #include "llvm/CodeGen/TargetSubtargetInfo.h"
+#include "llvm/Config/config.h"
 #include "llvm/DebugInfo/DWARF/DWARFDataExtractor.h"
 #include "llvm/DebugInfo/DWARF/DWARFExpression.h"
 #include "llvm/IR/Constants.h"
@@ -2080,6 +2081,10 @@ void DwarfDebug::beginInstruction(const MachineInstr *MI) {
   }
 
   if (!DL) {
+#ifdef LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING
+    assert(DL.getKind() != DebugLocKind::Temporary &&
+           "Temporary DebugLocs should never be considered for emission!");
+#endif
     // We have an unspecified location, which might want to be line 0.
     // If we have already emitted a line-0 record, don't repeat it.
     if (LastAsmLine == 0)

llvm/lib/CodeGen/BranchFolding.cpp

@@ -841,7 +841,7 @@ void BranchFolder::mergeCommonTails(unsigned commonTailIndex) {
             "Reached BB end within common tail");
       }
       assert(MI.isIdenticalTo(*Pos) && "Expected matching MIIs!");
-      DL = DILocation::getMergedLocation(DL, Pos->getDebugLoc());
+      DL = DebugLoc::getMergedLocation(DL, Pos->getDebugLoc());
       NextCommonInsts[i] = ++Pos;
     }
     MI.setDebugLoc(DL);
@@ -915,7 +915,7 @@ bool BranchFolder::TryTailMergeBlocks(MachineBasicBlock *SuccBB,
   // Walk through equivalence sets looking for actual exact matches.
   while (MergePotentials.size() > 1) {
     unsigned CurHash = MergePotentials.back().getHash();
-    const DebugLoc &BranchDL = MergePotentials.back().getBranchDebugLoc();
+    const DebugLoc BranchDL = MergePotentials.back().getBranchDebugLoc();
 
     // Build SameTails, identifying the set of blocks with this hash code
     // and with the maximum number of instructions in common.