[DLCov 3/5] Implement DebugLoc origin-tracking

clang/lib/CodeGen/BackendUtil.cpp

@@ -911,6 +911,22 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
       Debugify.setOrigDIVerifyBugsReportFilePath(
           CodeGenOpts.DIBugsReportFilePath);
     Debugify.registerCallbacks(PIC, MAM);
+
+#if 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) {

llvm/CMakeLists.txt

@@ -524,6 +524,10 @@ endif()
 
 option(LLVM_ENABLE_CRASH_DUMPS "Turn on memory dumps on crashes. Currently only implemented on Windows." OFF)
 
+set(LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING "DISABLED" CACHE STRING
+  "Enhance debugify's line number coverage tracking; enabling this is abi-breaking. Can be DISABLED, COVERAGE, or COVERAGE_AND_ORIGIN.")
+set_property(CACHE LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING PROPERTY STRINGS DISABLED COVERAGE COVERAGE_AND_ORIGIN)
+
 set(WINDOWS_PREFER_FORWARD_SLASH_DEFAULT OFF)
 if (MINGW)
   # Cygwin doesn't identify itself as Windows, and thus gets path::Style::posix

llvm/cmake/modules/HandleLLVMOptions.cmake

@@ -196,6 +196,19 @@ else()
   message(FATAL_ERROR "Unknown value for LLVM_ABI_BREAKING_CHECKS: \"${LLVM_ABI_BREAKING_CHECKS}\"!")
 endif()
 
+string(TOUPPER "${LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING}" uppercase_LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING)
+
+if( uppercase_LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING STREQUAL "COVERAGE" )
+  set( ENABLE_DEBUGLOC_COVERAGE_TRACKING 1 )
+elseif( uppercase_LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING STREQUAL "COVERAGE_AND_ORIGIN" )
+  set( ENABLE_DEBUGLOC_COVERAGE_TRACKING 1 )
+  set( ENABLE_DEBUGLOC_ORIGIN_TRACKING 1 )
+elseif( uppercase_LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING STREQUAL "DISABLED" OR NOT DEFINED LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING )
+  # The DISABLED setting is default and requires no additional defines.
+else()
+  message(FATAL_ERROR "Unknown value for LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING: \"${LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING}\"!")
+endif()
+
 if( LLVM_REVERSE_ITERATION )
   set( LLVM_ENABLE_REVERSE_ITERATION 1 )
 endif()

llvm/docs/CMake.rst

@@ -475,6 +475,17 @@ enabled sub-projects. Nearly all of these variable names begin with
 **LLVM_ENABLE_BINDINGS**:BOOL
   If disabled, do not try to build the OCaml bindings.
 
+**LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING**:STRING
+  Enhances Debugify's ability to detect line number errors by storing extra
+  information inside Instructions, removing false positives from Debugify's
+  results at the cost of performance. Allowed values are `DISABLED` (default),
+  `COVERAGE`, and `COVERAGE_AND_ORIGIN`. `COVERAGE` tracks whether and why a
+  line number was intentionally dropped or not generated for an instruction,
+  allowing Debugify to avoid reporting these as errors. `COVERAGE_AND_ORIGIN`
+  additionally stores a stacktrace of the point where each DebugLoc is
+  unintentionally dropped, allowing for much easier bug triaging at the cost of
+  a ~10x performance slowdown.
+
 **LLVM_ENABLE_DIA_SDK**:BOOL
   Enable building with MSVC DIA SDK for PDB debugging support. Available
   only with MSVC. Defaults to ON.

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

@@ -19,6 +19,14 @@
 /* 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 ENABLE_DEBUGLOC_COVERAGE_TRACKING
+
+/* Define to 1 to enable expensive tracking of the origin of debug location
+   coverage bugs, and to 0 otherwise. */
+#cmakedefine01 ENABLE_DEBUGLOC_ORIGIN_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 +23,90 @@ namespace llvm {
   class LLVMContext;
   class raw_ostream;
   class DILocation;
+  class Function;
+
+#if ENABLE_DEBUGLOC_COVERAGE_TRACKING
+#if ENABLE_DEBUGLOC_ORIGIN_TRACKING
+  struct DbgLocOrigin {
+    static constexpr unsigned long MaxDepth = 16;
+    using StackTracesTy =
+        SmallVector<std::pair<int, std::array<void *, MaxDepth>>, 0>;
+    StackTracesTy StackTraces;
+    DbgLocOrigin(bool ShouldCollectTrace);
+    void addTrace();
+    const StackTracesTy &getOriginStackTraces() const { return StackTraces; };
+  };
+#else
+  struct DbgLocOrigin {
+    DbgLocOrigin(bool) {}
+  };
+#endif
+
+  // 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 is expected to 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,
+    // e.g. the attribution is ambiguous in a way that can't be represented, or
+    // determining the correct location is complicated and requires future
+    // developer effort.
+    Unknown,
+    // DebugLoc is attached to an instruction that we don't expect to be
+    // emitted, and so can omit a valid DILocation; we don't expect to ever try
+    // and emit these into the line table, and trying to do so is a sign that
+    // something has gone wrong (most likely a DebugLoc leaking from a transient
+    // compiler-generated instruction).
+    Temporary
+  };
+
+  // Extends TrackingMDNodeRef to also store a DebugLocKind and Origin,
+  // allowing Debugify to ignore intentionally-empty DebugLocs and display the
+  // code responsible for generating unintentionally-empty DebugLocs.
+  // Currently we only need to track the Origin of this DILoc when using a
+  // DebugLoc that is not annotated (i.e. has DebugLocKind::Normal) and has a
+  // null DILocation, so only collect the origin stacktrace in those cases.
+  class DILocAndCoverageTracking : public TrackingMDNodeRef,
+                                   public DbgLocOrigin {
+  public:
+    DebugLocKind Kind;
+    // Default constructor for empty DebugLocs.
+    DILocAndCoverageTracking()
+        : TrackingMDNodeRef(nullptr), DbgLocOrigin(true),
+          Kind(DebugLocKind::Normal) {}
+    // Valid or nullptr MDNode*, normal DebugLocKind
+    DILocAndCoverageTracking(const MDNode *Loc)
+        : TrackingMDNodeRef(const_cast<MDNode *>(Loc)), DbgLocOrigin(!Loc),
+          Kind(DebugLocKind::Normal) {}
+    DILocAndCoverageTracking(const DILocation *Loc);
+    // Always nullptr MDNode*, any DebugLocKind
+    DILocAndCoverageTracking(DebugLocKind Kind)
+        : TrackingMDNodeRef(nullptr),
+          DbgLocOrigin(Kind == DebugLocKind::Normal), Kind(Kind) {}
+  };
+  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 // ENABLE_DEBUGLOC_COVERAGE_TRACKING
 
   /// A debug info location.
   ///
@@ -31,7 +116,8 @@ 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 +133,32 @@ namespace llvm {
     /// IR.
     explicit DebugLoc(const MDNode *N);
 
+#if ENABLE_DEBUGLOC_COVERAGE_TRACKING
+    DebugLoc(DebugLocKind Kind) : Loc(Kind) {}
+    DebugLocKind getKind() const { return Loc.Kind; }
+#endif
+
+#if ENABLE_DEBUGLOC_ORIGIN_TRACKING
+#if !ENABLE_DEBUGLOC_COVERAGE_TRACKING
+#error Cannot enable DebugLoc origin-tracking without coverage-tracking!
+#endif
+
+    const DbgLocOrigin::StackTracesTy &getOriginStackTraces() const {
+      return Loc.getOriginStackTraces();
+    }
+    DebugLoc getCopied() const {
+      DebugLoc NewDL = *this;
+      NewDL.Loc.addTrace();
+      return NewDL;
+    }
+#else
+    DebugLoc getCopied() const { return *this; }
+#endif
+
+    static DebugLoc getTemporary();
+    static DebugLoc getUnknown();
+    static DebugLoc getLineZero();
+
     /// Get the underlying \a DILocation.
     ///
     /// \pre !*this or \c isa<DILocation>(getAsMDNode()).

llvm/include/llvm/Support/Signals.h

@@ -14,13 +14,31 @@
 #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;
 
+#if ENABLE_DEBUGLOC_ORIGIN_TRACKING
+// Typedefs that are convenient but only used by the stack-trace-collection code
+// added if DebugLoc origin-tracking is enabled.
+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 +73,28 @@ namespace sys {
   ///        specified, the entire frame is printed.
   void PrintStackTrace(raw_ostream &OS, int Depth = 0);
 
+#if ENABLE_DEBUGLOC_ORIGIN_TRACKING
+#ifdef NDEBUG
+#error DebugLoc origin-tracking should not be enabled in Release builds.
+#endif
+  /// Populates the given array with a stack trace of the current program, up to
+  /// MaxDepth frames. Returns the number of frames returned, which will be
+  /// inserted into \p StackTrace from index 0. All entries after the returned
+  /// depth will be unmodified. NB: This is only intended to be used for
+  /// introspection of LLVM by Debugify, will not be enabled in release builds,
+  /// and should not be relied on for other purposes.
+  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.
+  /// NB: This is only intended to be used for introspection of LLVM by
+  /// Debugify, will not be enabled in release builds, and should not be relied
+  /// on for other purposes.
+  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) {
+    // FIXME: We could assert that `DL.getKind() != DebugLocKind::Temporary`
+    // here, or otherwise record any temporary DebugLocs seen to ensure that
+    // transient compiler-generated instructions aren't leaking their DLs to
+    // other instructions.
     // 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

@@ -41,6 +41,7 @@
 #include "llvm/CodeGen/TargetPassConfig.h"
 #include "llvm/CodeGen/TargetRegisterInfo.h"
 #include "llvm/CodeGen/TargetSubtargetInfo.h"
+#include "llvm/Config/config.h"
 #include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/DebugLoc.h"
 #include "llvm/IR/Function.h"
@@ -910,7 +911,13 @@ bool BranchFolder::TryTailMergeBlocks(MachineBasicBlock *SuccBB,
 
   // Sort by hash value so that blocks with identical end sequences sort
   // together.
+#if ENABLE_DEBUGLOC_ORIGIN_TRACKING
+  // If origin-tracking is enabled then MergePotentialElt is no longer a POD
+  // type, so we need std::sort instead.
+  std::sort(MergePotentials.begin(), MergePotentials.end());
+#else
   array_pod_sort(MergePotentials.begin(), MergePotentials.end());
+#endif
 
   // Walk through equivalence sets looking for actual exact matches.
   while (MergePotentials.size() > 1) {

llvm/lib/IR/DebugInfo.cpp

@@ -979,7 +979,7 @@ void Instruction::dropLocation() {
   }
 
   if (!MayLowerToCall) {
-    setDebugLoc(DebugLoc());
+    setDebugLoc(DebugLoc::getLineZero());
     return;
   }
 
@@ -998,7 +998,7 @@ void Instruction::dropLocation() {
     //
     // One alternative is to set a line 0 location with the existing scope and
     // inlinedAt info. The location might be sensitive to when inlining occurs.
-    setDebugLoc(DebugLoc());
+    setDebugLoc(DebugLoc::getLineZero());
 }
 
 //===----------------------------------------------------------------------===//

llvm/lib/IR/DebugLoc.cpp

@@ -9,8 +9,44 @@
 #include "llvm/IR/DebugLoc.h"
 #include "llvm/Config/llvm-config.h"
 #include "llvm/IR/DebugInfo.h"
+
+#if ENABLE_DEBUGLOC_ORIGIN_TRACKING
+#include "llvm/Support/Signals.h"
+
+namespace llvm {
+DbgLocOrigin::DbgLocOrigin(bool ShouldCollectTrace) {
+  if (ShouldCollectTrace) {
+    auto &[Depth, StackTrace] = StackTraces.emplace_back();
+    Depth = sys::getStackTrace(StackTrace);
+  }
+}
+void DbgLocOrigin::addTrace() {
+  if (StackTraces.empty())
+    return;
+  auto &[Depth, StackTrace] = StackTraces.emplace_back();
+  Depth = sys::getStackTrace(StackTrace);
+}
+} // namespace llvm
+#endif
+
 using namespace llvm;
 
+#if ENABLE_DEBUGLOC_COVERAGE_TRACKING
+DILocAndCoverageTracking::DILocAndCoverageTracking(const DILocation *L)
+    : TrackingMDNodeRef(const_cast<DILocation *>(L)), DbgLocOrigin(!L),
+      Kind(DebugLocKind::Normal) {}
+
+DebugLoc DebugLoc::getTemporary() { return DebugLoc(DebugLocKind::Temporary); }
+DebugLoc DebugLoc::getUnknown() { return DebugLoc(DebugLocKind::Unknown); }
+DebugLoc DebugLoc::getLineZero() { return DebugLoc(DebugLocKind::LineZero); }
+
+#else
+
+DebugLoc DebugLoc::getTemporary() { return DebugLoc(); }
+DebugLoc DebugLoc::getUnknown() { return DebugLoc(); }
+DebugLoc DebugLoc::getLineZero() { return DebugLoc(); }
+#endif // ENABLE_DEBUGLOC_COVERAGE_TRACKING
+
 //===----------------------------------------------------------------------===//
 // DebugLoc Implementation
 //===----------------------------------------------------------------------===//