2 files changed, 289 insertions, 89 deletions

diff --git a/include/llvm/ProfileData/Coverage/CoverageMapping.h b/include/llvm/ProfileData/Coverage/CoverageMapping.h
index fa9a87aed6806..5a4098cf666c4 100644
--- a/include/llvm/ProfileData/Coverage/CoverageMapping.h
+++ b/include/llvm/ProfileData/Coverage/CoverageMapping.h
@@ -85,7 +85,7 @@ private:
   coveragemap_error Err;
 };
 
-/// \brief A Counter is an abstract value that describes how to compute the
+/// A Counter is an abstract value that describes how to compute the
 /// execution count for a region of code using the collected profile count data.
 struct Counter {
   enum CounterKind { Zero, CounterValueReference, Expression };
@@ -125,23 +125,23 @@ public:
     return std::tie(LHS.Kind, LHS.ID) < std::tie(RHS.Kind, RHS.ID);
   }
 
-  /// \brief Return the counter that represents the number zero.
+  /// Return the counter that represents the number zero.
   static Counter getZero() { return Counter(); }
 
-  /// \brief Return the counter that corresponds to a specific profile counter.
+  /// Return the counter that corresponds to a specific profile counter.
   static Counter getCounter(unsigned CounterId) {
     return Counter(CounterValueReference, CounterId);
   }
 
-  /// \brief Return the counter that corresponds to a specific
-  /// addition counter expression.
+  /// Return the counter that corresponds to a specific addition counter
+  /// expression.
   static Counter getExpression(unsigned ExpressionId) {
     return Counter(Expression, ExpressionId);
   }
 };
 
-/// \brief A Counter expression is a value that represents an arithmetic
-/// operation with two counters.
+/// A Counter expression is a value that represents an arithmetic operation
+/// with two counters.
 struct CounterExpression {
   enum ExprKind { Subtract, Add };
   ExprKind Kind;
@@ -151,17 +151,16 @@ struct CounterExpression {
       : Kind(Kind), LHS(LHS), RHS(RHS) {}
 };
 
-/// \brief A Counter expression builder is used to construct the
-/// counter expressions. It avoids unnecessary duplication
-/// and simplifies algebraic expressions.
+/// A Counter expression builder is used to construct the counter expressions.
+/// It avoids unnecessary duplication and simplifies algebraic expressions.
 class CounterExpressionBuilder {
-  /// \brief A list of all the counter expressions
+  /// A list of all the counter expressions
   std::vector<CounterExpression> Expressions;
 
-  /// \brief A lookup table for the index of a given expression.
+  /// A lookup table for the index of a given expression.
   DenseMap<CounterExpression, unsigned> ExpressionIndices;
 
-  /// \brief Return the counter which corresponds to the given expression.
+  /// Return the counter which corresponds to the given expression.
   ///
   /// If the given expression is already stored in the builder, a counter
   /// that references that expression is returned. Otherwise, the given
@@ -177,44 +176,48 @@ class CounterExpressionBuilder {
         : CounterID(CounterID), Factor(Factor) {}
   };
 
-  /// \brief Gather the terms of the expression tree for processing.
+  /// Gather the terms of the expression tree for processing.
   ///
   /// This collects each addition and subtraction referenced by the counter into
   /// a sequence that can be sorted and combined to build a simplified counter
   /// expression.
   void extractTerms(Counter C, int Sign, SmallVectorImpl<Term> &Terms);
 
-  /// \brief Simplifies the given expression tree
+  /// Simplifies the given expression tree
   /// by getting rid of algebraically redundant operations.
   Counter simplify(Counter ExpressionTree);
 
 public:
   ArrayRef<CounterExpression> getExpressions() const { return Expressions; }
 
-  /// \brief Return a counter that represents the expression
-  /// that adds LHS and RHS.
+  /// Return a counter that represents the expression that adds LHS and RHS.
   Counter add(Counter LHS, Counter RHS);
 
-  /// \brief Return a counter that represents the expression
-  /// that subtracts RHS from LHS.
+  /// Return a counter that represents the expression that subtracts RHS from
+  /// LHS.
   Counter subtract(Counter LHS, Counter RHS);
 };
 
-/// \brief A Counter mapping region associates a source range with
-/// a specific counter.
+using LineColPair = std::pair<unsigned, unsigned>;
+
+/// A Counter mapping region associates a source range with a specific counter.
 struct CounterMappingRegion {
   enum RegionKind {
-    /// \brief A CodeRegion associates some code with a counter
+    /// A CodeRegion associates some code with a counter
     CodeRegion,
 
-    /// \brief An ExpansionRegion represents a file expansion region that
-    /// associates a source range with the expansion of a virtual source file,
-    /// such as for a macro instantiation or #include file.
+    /// An ExpansionRegion represents a file expansion region that associates 
+    /// a source range with the expansion of a virtual source file, such as
+    /// for a macro instantiation or #include file.
     ExpansionRegion,
 
-    /// \brief A SkippedRegion represents a source range with code that
-    /// was skipped by a preprocessor or similar means.
-    SkippedRegion
+    /// A SkippedRegion represents a source range with code that was skipped
+    /// by a preprocessor or similar means.
+    SkippedRegion,
+
+    /// A GapRegion is like a CodeRegion, but its count is only set as the
+    /// line execution count when its the only region in the line.
+    GapRegion
   };
 
   Counter Count;
@@ -251,16 +254,21 @@ struct CounterMappingRegion {
                                 LineEnd, ColumnEnd, SkippedRegion);
   }
 
-  inline std::pair<unsigned, unsigned> startLoc() const {
-    return std::pair<unsigned, unsigned>(LineStart, ColumnStart);
+  static CounterMappingRegion
+  makeGapRegion(Counter Count, unsigned FileID, unsigned LineStart,
+                unsigned ColumnStart, unsigned LineEnd, unsigned ColumnEnd) {
+    return CounterMappingRegion(Count, FileID, 0, LineStart, ColumnStart,
+                                LineEnd, (1U << 31) | ColumnEnd, GapRegion);
   }
 
-  inline std::pair<unsigned, unsigned> endLoc() const {
-    return std::pair<unsigned, unsigned>(LineEnd, ColumnEnd);
+  inline LineColPair startLoc() const {
+    return LineColPair(LineStart, ColumnStart);
   }
+
+  inline LineColPair endLoc() const { return LineColPair(LineEnd, ColumnEnd); }
 };
 
-/// \brief Associates a source range with an execution count.
+/// Associates a source range with an execution count.
 struct CountedRegion : public CounterMappingRegion {
   uint64_t ExecutionCount;
 
@@ -268,8 +276,8 @@ struct CountedRegion : public CounterMappingRegion {
       : CounterMappingRegion(R), ExecutionCount(ExecutionCount) {}
 };
 
-/// \brief A Counter mapping context is used to connect the counters,
-/// expressions and the obtained counter values.
+/// A Counter mapping context is used to connect the counters, expressions
+/// and the obtained counter values.
 class CounterMappingContext {
   ArrayRef<CounterExpression> Expressions;
   ArrayRef<uint64_t> CounterValues;
@@ -284,20 +292,20 @@ public:
   void dump(const Counter &C, raw_ostream &OS) const;
   void dump(const Counter &C) const { dump(C, dbgs()); }
 
-  /// \brief Return the number of times that a region of code associated with
-  /// this counter was executed.
+  /// Return the number of times that a region of code associated with this
+  /// counter was executed.
   Expected<int64_t> evaluate(const Counter &C) const;
 };
 
-/// \brief Code coverage information for a single function.
+/// Code coverage information for a single function.
 struct FunctionRecord {
-  /// \brief Raw function name.
+  /// Raw function name.
   std::string Name;
-  /// \brief Associated files.
+  /// Associated files.
   std::vector<std::string> Filenames;
-  /// \brief Regions in the function along with their counts.
+  /// Regions in the function along with their counts.
   std::vector<CountedRegion> CountedRegions;
-  /// \brief The number of times this function was executed.
+  /// The number of times this function was executed.
   uint64_t ExecutionCount;
 
   FunctionRecord(StringRef Name, ArrayRef<StringRef> Filenames)
@@ -313,7 +321,7 @@ struct FunctionRecord {
   }
 };
 
-/// \brief Iterator over Functions, optionally filtered to a single file.
+/// Iterator over Functions, optionally filtered to a single file.
 class FunctionRecordIterator
     : public iterator_facade_base<FunctionRecordIterator,
                                   std::forward_iterator_tag, FunctionRecord> {
@@ -321,7 +329,7 @@ class FunctionRecordIterator
   ArrayRef<FunctionRecord>::iterator Current;
   StringRef Filename;
 
-  /// \brief Skip records whose primary file is not \c Filename.
+  /// Skip records whose primary file is not \c Filename.
   void skipOtherFiles();
 
 public:
@@ -347,17 +355,17 @@ public:
   }
 };
 
-/// \brief Coverage information for a macro expansion or #included file.
+/// Coverage information for a macro expansion or #included file.
 ///
 /// When covered code has pieces that can be expanded for more detail, such as a
 /// preprocessor macro use and its definition, these are represented as
 /// expansions whose coverage can be looked up independently.
 struct ExpansionRecord {
-  /// \brief The abstract file this expansion covers.
+  /// The abstract file this expansion covers.
   unsigned FileID;
-  /// \brief The region that expands to this record.
+  /// The region that expands to this record.
   const CountedRegion &Region;
-  /// \brief Coverage for the expansion.
+  /// Coverage for the expansion.
   const FunctionRecord &Function;
 
   ExpansionRecord(const CountedRegion &Region,
@@ -365,38 +373,99 @@ struct ExpansionRecord {
       : FileID(Region.ExpandedFileID), Region(Region), Function(Function) {}
 };
 
-/// \brief The execution count information starting at a point in a file.
+/// The execution count information starting at a point in a file.
 ///
 /// A sequence of CoverageSegments gives execution counts for a file in format
 /// that's simple to iterate through for processing.
 struct CoverageSegment {
-  /// \brief The line where this segment begins.
+  /// The line where this segment begins.
   unsigned Line;
-  /// \brief The column where this segment begins.
+  /// The column where this segment begins.
   unsigned Col;
-  /// \brief The execution count, or zero if no count was recorded.
+  /// The execution count, or zero if no count was recorded.
   uint64_t Count;
-  /// \brief When false, the segment was uninstrumented or skipped.
+  /// When false, the segment was uninstrumented or skipped.
   bool HasCount;
-  /// \brief Whether this enters a new region or returns to a previous count.
+  /// Whether this enters a new region or returns to a previous count.
   bool IsRegionEntry;
+  /// Whether this enters a gap region.
+  bool IsGapRegion;
 
   CoverageSegment(unsigned Line, unsigned Col, bool IsRegionEntry)
       : Line(Line), Col(Col), Count(0), HasCount(false),
-        IsRegionEntry(IsRegionEntry) {}
+        IsRegionEntry(IsRegionEntry), IsGapRegion(false) {}
 
   CoverageSegment(unsigned Line, unsigned Col, uint64_t Count,
-                  bool IsRegionEntry)
+                  bool IsRegionEntry, bool IsGapRegion = false)
       : Line(Line), Col(Col), Count(Count), HasCount(true),
-        IsRegionEntry(IsRegionEntry) {}
+        IsRegionEntry(IsRegionEntry), IsGapRegion(IsGapRegion) {}
 
   friend bool operator==(const CoverageSegment &L, const CoverageSegment &R) {
-    return std::tie(L.Line, L.Col, L.Count, L.HasCount, L.IsRegionEntry) ==
-           std::tie(R.Line, R.Col, R.Count, R.HasCount, R.IsRegionEntry);
+    return std::tie(L.Line, L.Col, L.Count, L.HasCount, L.IsRegionEntry,
+                    L.IsGapRegion) == std::tie(R.Line, R.Col, R.Count,
+                                               R.HasCount, R.IsRegionEntry,
+                                               R.IsGapRegion);
   }
 };
 
-/// \brief Coverage information to be processed or displayed.
+/// An instantiation group contains a \c FunctionRecord list, such that each
+/// record corresponds to a distinct instantiation of the same function.
+///
+/// Note that it's possible for a function to have more than one instantiation
+/// (consider C++ template specializations or static inline functions).
+class InstantiationGroup {
+  friend class CoverageMapping;
+
+  unsigned Line;
+  unsigned Col;
+  std::vector<const FunctionRecord *> Instantiations;
+
+  InstantiationGroup(unsigned Line, unsigned Col,
+                     std::vector<const FunctionRecord *> Instantiations)
+      : Line(Line), Col(Col), Instantiations(std::move(Instantiations)) {}
+
+public:
+  InstantiationGroup(const InstantiationGroup &) = delete;
+  InstantiationGroup(InstantiationGroup &&) = default;
+
+  /// Get the number of instantiations in this group.
+  size_t size() const { return Instantiations.size(); }
+
+  /// Get the line where the common function was defined.
+  unsigned getLine() const { return Line; }
+
+  /// Get the column where the common function was defined.
+  unsigned getColumn() const { return Col; }
+
+  /// Check if the instantiations in this group have a common mangled name.
+  bool hasName() const {
+    for (unsigned I = 1, E = Instantiations.size(); I < E; ++I)
+      if (Instantiations[I]->Name != Instantiations[0]->Name)
+        return false;
+    return true;
+  }
+
+  /// Get the common mangled name for instantiations in this group.
+  StringRef getName() const {
+    assert(hasName() && "Instantiations don't have a shared name");
+    return Instantiations[0]->Name;
+  }
+
+  /// Get the total execution count of all instantiations in this group.
+  uint64_t getTotalExecutionCount() const {
+    uint64_t Count = 0;
+    for (const FunctionRecord *F : Instantiations)
+      Count += F->ExecutionCount;
+    return Count;
+  }
+
+  /// Get the instantiations in this group.
+  ArrayRef<const FunctionRecord *> getInstantiations() const {
+    return Instantiations;
+  }
+};
+
+/// Coverage information to be processed or displayed.
 ///
 /// This represents the coverage of an entire file, expansion, or function. It
 /// provides a sequence of CoverageSegments to iterate through, as well as the
@@ -413,9 +482,11 @@ public:
 
   CoverageData(StringRef Filename) : Filename(Filename) {}
 
-  /// \brief Get the name of the file this data covers.
+  /// Get the name of the file this data covers.
   StringRef getFilename() const { return Filename; }
 
+  /// Get an iterator over the coverage segments for this object. The segments
+  /// are guaranteed to be uniqued and sorted by location.
   std::vector<CoverageSegment>::const_iterator begin() const {
     return Segments.begin();
   }
@@ -426,22 +497,23 @@ public:
 
   bool empty() const { return Segments.empty(); }
 
-  /// \brief Expansions that can be further processed.
+  /// Expansions that can be further processed.
   ArrayRef<ExpansionRecord> getExpansions() const { return Expansions; }
 };
 
-/// \brief The mapping of profile information to coverage data.
+/// The mapping of profile information to coverage data.
 ///
 /// This is the main interface to get coverage information, using a profile to
 /// fill out execution counts.
 class CoverageMapping {
   StringSet<> FunctionNames;
   std::vector<FunctionRecord> Functions;
-  unsigned MismatchedFunctionCount = 0;
+  std::vector<std::pair<std::string, uint64_t>> FuncHashMismatches;
+  std::vector<std::pair<std::string, uint64_t>> FuncCounterMismatches;
 
   CoverageMapping() = default;
 
-  /// \brief Add a function record corresponding to \p Record.
+  /// Add a function record corresponding to \p Record.
   Error loadFunctionRecord(const CoverageMappingRecord &Record,
                            IndexedInstrProfReader &ProfileReader);
 
@@ -449,59 +521,162 @@ public:
   CoverageMapping(const CoverageMapping &) = delete;
   CoverageMapping &operator=(const CoverageMapping &) = delete;
 
-  /// \brief Load the coverage mapping using the given readers.
+  /// Load the coverage mapping using the given readers.
   static Expected<std::unique_ptr<CoverageMapping>>
   load(ArrayRef<std::unique_ptr<CoverageMappingReader>> CoverageReaders,
        IndexedInstrProfReader &ProfileReader);
 
+  /// Load the coverage mapping from the given object files and profile. If
+  /// \p Arches is non-empty, it must specify an architecture for each object.
   static Expected<std::unique_ptr<CoverageMapping>>
   load(ArrayRef<StringRef> ObjectFilenames, StringRef ProfileFilename,
-       StringRef Arch = StringRef());
+       ArrayRef<StringRef> Arches = None);
 
-  /// \brief The number of functions that couldn't have their profiles mapped.
+  /// The number of functions that couldn't have their profiles mapped.
   ///
   /// This is a count of functions whose profile is out of date or otherwise
   /// can't be associated with any coverage information.
-  unsigned getMismatchedCount() { return MismatchedFunctionCount; }
+  unsigned getMismatchedCount() const {
+    return FuncHashMismatches.size() + FuncCounterMismatches.size();
+  }
+
+  /// A hash mismatch occurs when a profile record for a symbol does not have
+  /// the same hash as a coverage mapping record for the same symbol. This
+  /// returns a list of hash mismatches, where each mismatch is a pair of the
+  /// symbol name and its coverage mapping hash.
+  ArrayRef<std::pair<std::string, uint64_t>> getHashMismatches() const {
+    return FuncHashMismatches;
+  }
 
-  /// \brief Returns a lexicographically sorted, unique list of files that are
+  /// A counter mismatch occurs when there is an error when evaluating the
+  /// counter expressions in a coverage mapping record. This returns a list of
+  /// counter mismatches, where each mismatch is a pair of the symbol name and
+  /// the number of valid evaluated counter expressions.
+  ArrayRef<std::pair<std::string, uint64_t>> getCounterMismatches() const {
+    return FuncCounterMismatches;
+  }
+
+  /// Returns a lexicographically sorted, unique list of files that are
   /// covered.
   std::vector<StringRef> getUniqueSourceFiles() const;
 
-  /// \brief Get the coverage for a particular file.
+  /// Get the coverage for a particular file.
   ///
   /// The given filename must be the name as recorded in the coverage
   /// information. That is, only names returned from getUniqueSourceFiles will
   /// yield a result.
   CoverageData getCoverageForFile(StringRef Filename) const;
 
-  /// \brief Gets all of the functions covered by this profile.
+  /// Get the coverage for a particular function.
+  CoverageData getCoverageForFunction(const FunctionRecord &Function) const;
+
+  /// Get the coverage for an expansion within a coverage set.
+  CoverageData getCoverageForExpansion(const ExpansionRecord &Expansion) const;
+
+  /// Gets all of the functions covered by this profile.
   iterator_range<FunctionRecordIterator> getCoveredFunctions() const {
     return make_range(FunctionRecordIterator(Functions),
                       FunctionRecordIterator());
   }
 
-  /// \brief Gets all of the functions in a particular file.
+  /// Gets all of the functions in a particular file.
   iterator_range<FunctionRecordIterator>
   getCoveredFunctions(StringRef Filename) const {
     return make_range(FunctionRecordIterator(Functions, Filename),
                       FunctionRecordIterator());
   }
 
-  /// \brief Get the list of function instantiations in the file.
+  /// Get the list of function instantiation groups in a particular file.
   ///
-  /// Functions that are instantiated more than once, such as C++ template
-  /// specializations, have distinct coverage records for each instantiation.
-  std::vector<const FunctionRecord *>
-  getInstantiations(StringRef Filename) const;
+  /// Every instantiation group in a program is attributed to exactly one file:
+  /// the file in which the definition for the common function begins.
+  std::vector<InstantiationGroup>
+  getInstantiationGroups(StringRef Filename) const;
+};
 
-  /// \brief Get the coverage for a particular function.
-  CoverageData getCoverageForFunction(const FunctionRecord &Function) const;
+/// Coverage statistics for a single line.
+class LineCoverageStats {
+  uint64_t ExecutionCount;
+  bool HasMultipleRegions;
+  bool Mapped;
+  unsigned Line;
+  ArrayRef<const CoverageSegment *> LineSegments;
+  const CoverageSegment *WrappedSegment;
 
-  /// \brief Get the coverage for an expansion within a coverage set.
-  CoverageData getCoverageForExpansion(const ExpansionRecord &Expansion) const;
+  friend class LineCoverageIterator;
+  LineCoverageStats() = default;
+
+public:
+  LineCoverageStats(ArrayRef<const CoverageSegment *> LineSegments,
+                    const CoverageSegment *WrappedSegment, unsigned Line);
+
+  uint64_t getExecutionCount() const { return ExecutionCount; }
+
+  bool hasMultipleRegions() const { return HasMultipleRegions; }
+
+  bool isMapped() const { return Mapped; }
+
+  unsigned getLine() const { return Line; }
+
+  ArrayRef<const CoverageSegment *> getLineSegments() const {
+    return LineSegments;
+  }
+
+  const CoverageSegment *getWrappedSegment() const { return WrappedSegment; }
+};
+
+/// An iterator over the \c LineCoverageStats objects for lines described by
+/// a \c CoverageData instance.
+class LineCoverageIterator
+    : public iterator_facade_base<
+          LineCoverageIterator, std::forward_iterator_tag, LineCoverageStats> {
+public:
+  LineCoverageIterator(const CoverageData &CD)
+      : LineCoverageIterator(CD, CD.begin()->Line) {}
+
+  LineCoverageIterator(const CoverageData &CD, unsigned Line)
+      : CD(CD), WrappedSegment(nullptr), Next(CD.begin()), Ended(false),
+        Line(Line), Segments(), Stats() {
+    this->operator++();
+  }
+
+  LineCoverageIterator &operator=(const LineCoverageIterator &R) = default;
+
+  bool operator==(const LineCoverageIterator &R) const {
+    return &CD == &R.CD && Next == R.Next && Ended == R.Ended;
+  }
+
+  const LineCoverageStats &operator*() const { return Stats; }
+
+  LineCoverageStats &operator*() { return Stats; }
+
+  LineCoverageIterator &operator++();
+
+  LineCoverageIterator getEnd() const {
+    auto EndIt = *this;
+    EndIt.Next = CD.end();
+    EndIt.Ended = true;
+    return EndIt;
+  }
+
+private:
+  const CoverageData &CD;
+  const CoverageSegment *WrappedSegment;
+  std::vector<CoverageSegment>::const_iterator Next;
+  bool Ended;
+  unsigned Line;
+  SmallVector<const CoverageSegment *, 4> Segments;
+  LineCoverageStats Stats;
 };
 
+/// Get a \c LineCoverageIterator range for the lines described by \p CD.
+static inline iterator_range<LineCoverageIterator>
+getLineCoverageStats(const coverage::CoverageData &CD) {
+  auto Begin = LineCoverageIterator(CD);
+  auto End = Begin.getEnd();
+  return make_range(Begin, End);
+}
+
 // Profile coverage map has the following layout:
 // [CoverageMapFileHeader]
 // [ArrayStart]
@@ -602,7 +777,10 @@ enum CovMapVersion {
   // name string pointer to MD5 to support name section compression. Name
   // section is also compressed.
   Version2 = 1,
-  // The current version is Version2
+  // A new interpretation of the columnEnd field is added in order to mark
+  // regions as gap areas.
+  Version3 = 2,
+  // The current version is Version3
   CurrentVersion = INSTR_PROF_COVMAP_VERSION
 };
 
@@ -618,7 +796,7 @@ template <class IntPtrT> struct CovMapTraits<CovMapVersion::Version1, IntPtrT> {
 
 } // end namespace coverage
 
-/// \brief Provide DenseMapInfo for CounterExpression
+/// Provide DenseMapInfo for CounterExpression
 template<> struct DenseMapInfo<coverage::CounterExpression> {
   static inline coverage::CounterExpression getEmptyKey() {
     using namespace coverage;
diff --git a/include/llvm/ProfileData/Coverage/CoverageMappingReader.h b/include/llvm/ProfileData/Coverage/CoverageMappingReader.h
index 5b372252a9ac9..633e51565cd2a 100644
--- a/include/llvm/ProfileData/Coverage/CoverageMappingReader.h
+++ b/include/llvm/ProfileData/Coverage/CoverageMappingReader.h
@@ -44,18 +44,26 @@ struct CoverageMappingRecord {
 /// \brief A file format agnostic iterator over coverage mapping data.
 class CoverageMappingIterator
     : public std::iterator<std::input_iterator_tag, CoverageMappingRecord> {
-  CoverageMappingReader *Reader = nullptr;
+  CoverageMappingReader *Reader;
   CoverageMappingRecord Record;
+  coveragemap_error ReadErr;
 
   void increment();
 
 public:
-  CoverageMappingIterator() = default;
+  CoverageMappingIterator()
+      : Reader(nullptr), Record(), ReadErr(coveragemap_error::success) {}
 
-  CoverageMappingIterator(CoverageMappingReader *Reader) : Reader(Reader) {
+  CoverageMappingIterator(CoverageMappingReader *Reader)
+      : Reader(Reader), Record(), ReadErr(coveragemap_error::success) {
     increment();
   }
 
+  ~CoverageMappingIterator() {
+    if (ReadErr != coveragemap_error::success)
+      llvm_unreachable("Unexpected error in coverage mapping iterator");
+  }
+
   CoverageMappingIterator &operator++() {
     increment();
     return *this;
@@ -66,8 +74,22 @@ public:
   bool operator!=(const CoverageMappingIterator &RHS) {
     return Reader != RHS.Reader;
   }
-  CoverageMappingRecord &operator*() { return Record; }
-  CoverageMappingRecord *operator->() { return &Record; }
+  Expected<CoverageMappingRecord &> operator*() {
+    if (ReadErr != coveragemap_error::success) {
+      auto E = make_error<CoverageMapError>(ReadErr);
+      ReadErr = coveragemap_error::success;
+      return std::move(E);
+    }
+    return Record;
+  }
+  Expected<CoverageMappingRecord *> operator->() {
+    if (ReadErr != coveragemap_error::success) {
+      auto E = make_error<CoverageMapError>(ReadErr);
+      ReadErr = coveragemap_error::success;
+      return std::move(E);
+    }
+    return &Record;
+  }
 };
 
 class CoverageMappingReader {