Index: tools/llvm-exegesis/lib/Analysis.h
===================================================================
--- tools/llvm-exegesis/lib/Analysis.h
+++ tools/llvm-exegesis/lib/Analysis.h
@@ -40,7 +40,9 @@
   template <typename Pass> llvm::Error run(llvm::raw_ostream &OS) const;
 
 private:
-  void printInstructionRow(bool PrintSchedClass, size_t PointId,
+  void printInstructionRowCsv(size_t PointId, llvm::raw_ostream &OS) const;
+
+  void printSchedClassHtml(std::vector<size_t> PointIds,
                            llvm::raw_ostream &OS) const;
 
   // Builds a map of Sched Class -> indices of points that belong to the sched
Index: tools/llvm-exegesis/lib/Analysis.cpp
===================================================================
--- tools/llvm-exegesis/lib/Analysis.cpp
+++ tools/llvm-exegesis/lib/Analysis.cpp
@@ -17,7 +17,15 @@
 
 static const char kCsvSep = ',';
 
-static void writeCsvEscaped(llvm::raw_ostream &OS, const std::string &S) {
+namespace {
+
+enum EscapeTag { kEscapeCsv, kEscapeHtml };
+
+template <EscapeTag Tag>
+void writeEscaped(llvm::raw_ostream &OS, const llvm::StringRef S);
+
+template <>
+void writeEscaped<kEscapeCsv>(llvm::raw_ostream &OS, const llvm::StringRef S) {
   if (std::find(S.begin(), S.end(), kCsvSep) == S.end()) {
     OS << S;
   } else {
@@ -33,44 +41,68 @@
   }
 }
 
+template <>
+void writeEscaped<kEscapeHtml>(llvm::raw_ostream &OS, const llvm::StringRef S) {
+  for (const char C : S) {
+    if (C == '<')
+      OS << "&lt;";
+    else if (C == '>')
+      OS << "&gt;";
+    else if (C == '&')
+      OS << "&amp;";
+    else
+      OS << C;
+  }
+}
+
+} // namespace
+
+template <EscapeTag Tag>
+static void
+writeClusterId(llvm::raw_ostream &OS,
+               const InstructionBenchmarkClustering::ClusterId &CID) {
+  if (CID.isNoise())
+    writeEscaped<Tag>(OS, "[noise]");
+  else if (CID.isError())
+    writeEscaped<Tag>(OS, "[error]");
+  else
+    OS << CID.getId();
+}
+
+template <EscapeTag Tag>
+static void writeMeasurementValue(llvm::raw_ostream &OS, const double Value) {
+  writeEscaped<Tag>(OS, llvm::formatv("{0:F}", Value).str());
+}
+
 // Prints a row representing an instruction, along with scheduling info and
 // point coordinates (measurements).
-void Analysis::printInstructionRow(const bool PrintSchedClass,
-                                   const size_t PointId,
-                                   llvm::raw_ostream &OS) const {
+void Analysis::printInstructionRowCsv(const size_t PointId,
+                                      llvm::raw_ostream &OS) const {
   const InstructionBenchmark &Point = Clustering_.getPoints()[PointId];
-  const auto &ClusterId = Clustering_.getClusterIdForPoint(PointId);
-  if (ClusterId.isNoise())
-    OS << "[noise]";
-  else if (ClusterId.isError())
-    OS << "[error]";
-  else
-    OS << ClusterId.getId();
+  writeClusterId<kEscapeCsv>(OS, Clustering_.getClusterIdForPoint(PointId));
   OS << kCsvSep;
-  writeCsvEscaped(OS, Point.Key.OpcodeName);
+  writeEscaped<kEscapeCsv>(OS, Point.Key.OpcodeName);
   OS << kCsvSep;
-  writeCsvEscaped(OS, Point.Key.Config);
-  if (PrintSchedClass) {
-    OS << kCsvSep;
-    const auto OpcodeIt = MnemonicToOpcode_.find(Point.Key.OpcodeName);
-    if (OpcodeIt != MnemonicToOpcode_.end()) {
-      const unsigned SchedClassId =
-          InstrInfo_->get(OpcodeIt->second).getSchedClass();
+  writeEscaped<kEscapeCsv>(OS, Point.Key.Config);
+  OS << kCsvSep;
+  const auto OpcodeIt = MnemonicToOpcode_.find(Point.Key.OpcodeName);
+  if (OpcodeIt != MnemonicToOpcode_.end()) {
+    const unsigned SchedClassId =
+        InstrInfo_->get(OpcodeIt->second).getSchedClass();
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
-      const auto &SchedModel = SubtargetInfo_->getSchedModel();
-      const llvm::MCSchedClassDesc *const SCDesc =
-          SchedModel.getSchedClassDesc(SchedClassId);
-      writeCsvEscaped(OS, SCDesc->Name);
+    const auto &SchedModel = SubtargetInfo_->getSchedModel();
+    const llvm::MCSchedClassDesc *const SCDesc =
+        SchedModel.getSchedClassDesc(SchedClassId);
+    writeEscaped<kEscapeCsv>(OS, SCDesc->Name);
 #else
-      OS << SchedClassId;
+    OS << SchedClassId;
 #endif
-    }
   }
   // FIXME: Print the sched class once InstructionBenchmark separates key into
   // (mnemonic, mode, opaque).
   for (const auto &Measurement : Point.Measurements) {
     OS << kCsvSep;
-    writeCsvEscaped(OS, llvm::formatv("{0:F}", Measurement.Value));
+    writeMeasurementValue<kEscapeCsv>(OS, Measurement.Value);
   }
   OS << "\n";
 }
@@ -102,7 +134,7 @@
      << kCsvSep << "sched_class";
   for (const auto &Measurement : Clustering_.getPoints().front().Measurements) {
     OS << kCsvSep;
-    writeCsvEscaped(OS, Measurement.Key);
+    writeEscaped<kEscapeCsv>(OS, Measurement.Key);
   }
   OS << "\n";
 
@@ -110,7 +142,7 @@
   const auto &Clusters = Clustering_.getValidClusters();
   for (size_t I = 0, E = Clusters.size(); I < E; ++I) {
     for (const size_t PointId : Clusters[I].PointIndices) {
-      printInstructionRow(/*PrintSchedClass*/ true, PointId, OS);
+      printInstructionRowCsv(PointId, OS);
     }
     OS << "\n\n";
   }
@@ -135,9 +167,110 @@
   return PointsPerSchedClass;
 }
 
+void Analysis::printSchedClassHtml(std::vector<size_t> PointIds,
+                                   llvm::raw_ostream &OS) const {
+  assert(!PointIds.empty());
+  // Sort the points by cluster id so that we can display them grouped by
+  // cluster.
+  std::sort(PointIds.begin(), PointIds.end(),
+            [this](const size_t A, const size_t B) {
+              return Clustering_.getClusterIdForPoint(A) <
+                     Clustering_.getClusterIdForPoint(B);
+            });
+  const auto &Points = Clustering_.getPoints();
+  OS << "<table class=\"sched-class\">";
+  OS << "<tr><th>ClusterId</th><th>Opcode/Config</th>";
+  for (const auto &Measurement : Points[PointIds[0]].Measurements) {
+    OS << "<th>";
+    writeEscaped<kEscapeHtml>(OS, Measurement.Key);
+    OS << "</th>";
+  }
+  OS << "</tr>";
+  for (size_t I = 0, E = PointIds.size(); I < E;) {
+    const auto &CurrentClusterId =
+        Clustering_.getClusterIdForPoint(PointIds[I]);
+    OS << "<tr><td>";
+    writeClusterId<kEscapeHtml>(OS, CurrentClusterId);
+    OS << "</td><td><ul>";
+    const auto &ClusterRepresentative =
+        Points[PointIds[I]]; // FIXME: average measurements.
+    for (; I < E &&
+           Clustering_.getClusterIdForPoint(PointIds[I]) == CurrentClusterId;
+         ++I) {
+      OS << "<li><span class=\"mono\">";
+      writeEscaped<kEscapeHtml>(OS, Points[PointIds[I]].Key.OpcodeName);
+      OS << "</span> <span class=\"mono\">";
+      writeEscaped<kEscapeHtml>(OS, Points[PointIds[I]].Key.Config);
+      OS << "</span></li>";
+    }
+    OS << "</ul></td>";
+    for (const auto &Measurement : ClusterRepresentative.Measurements) {
+      OS << "<td>";
+      writeMeasurementValue<kEscapeHtml>(OS, Measurement.Value);
+      OS << "</td>";
+    }
+    OS << "</tr>";
+  }
+  OS << "</table>";
+}
+
+static constexpr const char kHtmlHead[] = R"(
+<head>
+<title>llvm-exegesis Analysis Results</title>
+<style>
+body {
+  font-family: sans-serif
+}
+span.sched-class-name {
+  font-weight: bold;
+  font-family: monospace;
+}
+span.opcode {
+  font-family: monospace;
+}
+span.config {
+  font-family: monospace;
+}
+div.inconsistency {
+  margin-top: 50px;
+}
+table.sched-class {
+  margin-left: 50px;
+  border-collapse: collapse;
+}
+table.sched-class, table.sched-class tr,td,th {
+  border: 1px solid #444;
+}
+table.sched-class td {
+  padding-left: 10px;
+  padding-right: 10px;
+  padding-top: 10px;
+  padding-bottom: 10px;
+}
+table.sched-class ul {
+  padding-left: 0px;
+  margin: 0px;
+  list-style-type: none;
+}
+span.mono {
+  font-family: monospace;
+}
+</style>
+</head>
+)";
+
 template <>
 llvm::Error Analysis::run<Analysis::PrintSchedClassInconsistencies>(
     llvm::raw_ostream &OS) const {
+  // Print the header.
+  OS << "<!DOCTYPE html><html>" << kHtmlHead << "<body>";
+  OS << "<h1><span class=\"mono\">llvm-exegesis</span> Analysis Results</h1>";
+  OS << "<h3>Triple: <span class=\"mono\">";
+  writeEscaped<kEscapeHtml>(OS, Clustering_.getPoints()[0].LLVMTriple);
+  OS << "</span></h3><h3>Cpu: <span class=\"mono\">";
+  writeEscaped<kEscapeHtml>(OS, Clustering_.getPoints()[0].CpuName);
+  OS << "</span></h3>";
+
   // All the points in a scheduling class should be in the same cluster.
   // Print any scheduling class for which this is not the case.
   for (const auto &SchedClassAndPoints : makePointsPerSchedClass()) {
@@ -151,22 +284,24 @@
     if (ClustersForSchedClass.size() <= 1)
       continue; // Nothing weird.
 
-    OS << "\nSched Class ";
+    OS << "<div class=\"inconsistency\"><p>Sched Class <span "
+          "class=\"sched-class-name\">";
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
     const auto &SchedModel = SubtargetInfo_->getSchedModel();
     const llvm::MCSchedClassDesc *const SCDesc =
         SchedModel.getSchedClassDesc(SchedClassAndPoints.first);
-    OS << SCDesc->Name;
+    writeEscaped<kEscapeHtml>(OS, SCDesc->Name);
 #else
     OS << SchedClassAndPoints.first;
 #endif
-    OS << " contains instructions with distinct performance "
+    OS << "</span> contains instructions with distinct performance "
           "characteristics, falling into "
-       << ClustersForSchedClass.size() << " clusters:\n";
-    for (const size_t PointId : SchedClassAndPoints.second) {
-      printInstructionRow(/*PrintSchedClass*/ false, PointId, OS);
-    }
+       << ClustersForSchedClass.size() << " clusters:</p>";
+    printSchedClassHtml(SchedClassAndPoints.second, OS);
+    OS << "</div>";
   }
+
+  OS << "</body></html>";
   return llvm::Error::success();
 }
 
Index: tools/llvm-exegesis/lib/Clustering.h
===================================================================
--- tools/llvm-exegesis/lib/Clustering.h
+++ tools/llvm-exegesis/lib/Clustering.h
@@ -33,14 +33,14 @@
   public:
     static ClusterId noise() { return ClusterId(kNoise); }
     static ClusterId error() { return ClusterId(kError); }
-    static ClusterId makeValid(int Id) {
-      assert(Id >= 0);
+    static ClusterId makeValid(size_t Id) {
       return ClusterId(Id);
     }
     ClusterId() : Id_(kUndef) {}
     bool operator==(const ClusterId &O) const { return Id_ == O.Id_; }
+    bool operator<(const ClusterId &O) const {return Id_ < O.Id_; }
 
-    bool isValid() const { return Id_ >= 0; }
+    bool isValid() const { return Id_ <= kMaxValid; }
     bool isUndef() const { return Id_ == kUndef; }
     bool isNoise() const { return Id_ == kNoise; }
     bool isError() const { return Id_ == kError; }
@@ -48,15 +48,16 @@
     // Precondition: isValid().
     size_t getId() const {
       assert(isValid());
-      return static_cast<size_t>(Id_);
+      return Id_;
     }
 
   private:
-    explicit ClusterId(int Id) : Id_(Id) {}
-    static constexpr const int kUndef = -1;
-    static constexpr const int kNoise = -2;
-    static constexpr const int kError = -3;
-    int Id_;
+    explicit ClusterId(size_t Id) : Id_(Id) {}
+    static constexpr const size_t kMaxValid = std::numeric_limits<size_t>::max() - 4;
+    static constexpr const size_t kNoise = kMaxValid + 1;
+    static constexpr const size_t kError = kMaxValid + 2;
+    static constexpr const size_t kUndef = kMaxValid + 3;
+    size_t Id_;
   };
 
   struct Cluster {
Index: unittests/tools/llvm-exegesis/ClusteringTest.cpp
===================================================================
--- unittests/tools/llvm-exegesis/ClusteringTest.cpp
+++ unittests/tools/llvm-exegesis/ClusteringTest.cpp
@@ -82,5 +82,19 @@
   consumeError(std::move(Error));
 }
 
+TEST(ClusteringTest, Ordering) {
+  ASSERT_LT(InstructionBenchmarkClustering::ClusterId::makeValid(1),
+            InstructionBenchmarkClustering::ClusterId::makeValid(2));
+
+  ASSERT_LT(InstructionBenchmarkClustering::ClusterId::makeValid(2),
+            InstructionBenchmarkClustering::ClusterId::noise());
+
+  ASSERT_LT(InstructionBenchmarkClustering::ClusterId::makeValid(2),
+            InstructionBenchmarkClustering::ClusterId::error());
+
+  ASSERT_LT(InstructionBenchmarkClustering::ClusterId::noise(),
+            InstructionBenchmarkClustering::ClusterId::error());
+}
+
 } // namespace
 } // namespace exegesis