diff --git a/llvm/docs/CommandGuide/llvm-cov.rst b/llvm/docs/CommandGuide/llvm-cov.rst
--- a/llvm/docs/CommandGuide/llvm-cov.rst
+++ b/llvm/docs/CommandGuide/llvm-cov.rst
@@ -249,6 +249,12 @@
  line, but show the individual regions if there are multiple on the line.
  Defaults to false.
 
+.. option:: -show-directory-coverage
+
+ Generate index files in each level of the directory to show the coverage.
+ Defaults to false and a single index file will be generated in the output
+ directory (which can be very large and impossible to read for large projects).
+
 .. option:: -use-color
 
  Enable or disable color output. By default this is autodetected.
diff --git a/llvm/test/tools/llvm-cov/Inputs/directory_coverage/a0/a1/a2.cc b/llvm/test/tools/llvm-cov/Inputs/directory_coverage/a0/a1/a2.cc
new file mode 100644
--- /dev/null
+++ b/llvm/test/tools/llvm-cov/Inputs/directory_coverage/a0/a1/a2.cc
@@ -0,0 +1,7 @@
+#include "../../header.h"
+
+template<>
+bool equal<int>(int a, int b)
+{
+  return a == b;
+}
diff --git a/llvm/test/tools/llvm-cov/Inputs/directory_coverage/b/b1.h b/llvm/test/tools/llvm-cov/Inputs/directory_coverage/b/b1.h
new file mode 100644
--- /dev/null
+++ b/llvm/test/tools/llvm-cov/Inputs/directory_coverage/b/b1.h
@@ -0,0 +1,3 @@
+int add(int a, int b);
+
+int sub(int a, int b);
diff --git a/llvm/test/tools/llvm-cov/Inputs/directory_coverage/b/b1_1.cc b/llvm/test/tools/llvm-cov/Inputs/directory_coverage/b/b1_1.cc
new file mode 100644
--- /dev/null
+++ b/llvm/test/tools/llvm-cov/Inputs/directory_coverage/b/b1_1.cc
@@ -0,0 +1,5 @@
+#include "b1.h"
+
+int add(int a, int b) {
+  return a + b;
+}
diff --git a/llvm/test/tools/llvm-cov/Inputs/directory_coverage/b/b1_2.cc b/llvm/test/tools/llvm-cov/Inputs/directory_coverage/b/b1_2.cc
new file mode 100644
--- /dev/null
+++ b/llvm/test/tools/llvm-cov/Inputs/directory_coverage/b/b1_2.cc
@@ -0,0 +1,5 @@
+#include "b1.h"
+
+int sub(int a, int b) {
+  return a - b;
+}
diff --git a/llvm/test/tools/llvm-cov/Inputs/directory_coverage/c0/c1/c2.h b/llvm/test/tools/llvm-cov/Inputs/directory_coverage/c0/c1/c2.h
new file mode 100644
--- /dev/null
+++ b/llvm/test/tools/llvm-cov/Inputs/directory_coverage/c0/c1/c2.h
@@ -0,0 +1,9 @@
+int mul(int a, int b);
+
+int div(int a, int b);
+
+#ifdef DEF
+int div(int a, int b) {
+  return a / b;
+}
+#endif
diff --git a/llvm/test/tools/llvm-cov/Inputs/directory_coverage/c0/c1/c2_1.cc b/llvm/test/tools/llvm-cov/Inputs/directory_coverage/c0/c1/c2_1.cc
new file mode 100644
--- /dev/null
+++ b/llvm/test/tools/llvm-cov/Inputs/directory_coverage/c0/c1/c2_1.cc
@@ -0,0 +1,3 @@
+int mul(int a, int b) {
+  return a * b;
+}
diff --git a/llvm/test/tools/llvm-cov/Inputs/directory_coverage/c0/c1/c2_2.cc b/llvm/test/tools/llvm-cov/Inputs/directory_coverage/c0/c1/c2_2.cc
new file mode 100644
--- /dev/null
+++ b/llvm/test/tools/llvm-cov/Inputs/directory_coverage/c0/c1/c2_2.cc
@@ -0,0 +1,2 @@
+#define DEF
+#include "c2.h"
diff --git a/llvm/test/tools/llvm-cov/Inputs/directory_coverage/header.h b/llvm/test/tools/llvm-cov/Inputs/directory_coverage/header.h
new file mode 100644
--- /dev/null
+++ b/llvm/test/tools/llvm-cov/Inputs/directory_coverage/header.h
@@ -0,0 +1,5 @@
+#include "b/b1.h"
+#include "c0/c1/c2.h"
+
+template<typename T>
+bool equal(T a, T b);
diff --git a/llvm/test/tools/llvm-cov/Inputs/directory_coverage/main.cc b/llvm/test/tools/llvm-cov/Inputs/directory_coverage/main.cc
new file mode 100644
--- /dev/null
+++ b/llvm/test/tools/llvm-cov/Inputs/directory_coverage/main.cc
@@ -0,0 +1,9 @@
+#include "header.h"
+
+int main() {
+  int a = 3;
+  int b = 4;
+  int c = c = add(a, b);
+  int d = mul(a, b);
+  return equal(a, sub(c, b)) - equal(a, div(d, b));
+}
diff --git a/llvm/test/tools/llvm-cov/directory_coverage.test b/llvm/test/tools/llvm-cov/directory_coverage.test
new file mode 100644
--- /dev/null
+++ b/llvm/test/tools/llvm-cov/directory_coverage.test
@@ -0,0 +1,37 @@
+// RUN: mkdir -p %t && clang -fprofile-instr-generate=%t/default.profraw -fcoverage-mapping -o %t/main.out \
+// RUN:   %S/Inputs/directory_coverage/main.cc \
+// RUN:   %S/Inputs/directory_coverage/a0/a1/a2.cc \
+// RUN:   %S/Inputs/directory_coverage/b/b1_1.cc \
+// RUN:   %S/Inputs/directory_coverage/b/b1_2.cc \
+// RUN:   %S/Inputs/directory_coverage/c0/c1/c2_1.cc \
+// RUN:   %S/Inputs/directory_coverage/c0/c1/c2_2.cc
+// RUN: %t/main.out
+// RUN: llvm-profdata merge %t/default.profraw -o %t/profdata
+// RUN: llvm-cov show %t/main.out --instr-profile %t/profdata --format=html --show-directory-coverage -o %t/report
+// RUN: cat %t/report/index.html | FileCheck %s --check-prefix=ROOT --allow-empty
+// RUN: cat %t/report/coverage/%:S/Inputs/directory_coverage/index.html | FileCheck %s --check-prefix=TOP
+// RUN: cat %t/report/coverage/%:S/Inputs/directory_coverage/b/index.html | FileCheck %s --check-prefix=B
+// RUN: cat %t/report/coverage/%:S/Inputs/directory_coverage/c0/c1/index.html | FileCheck %s --check-prefix=C1
+
+// ROOT: coverage{{.*}}Inputs{{/|\\}}directory_coverage{{/|\\}}index.html
+
+
+// TOP: a0{{/|\\}}a1{{/|\\}}a2.cc
+// TOP: b{{/|\\}}
+// TOP-NOT: b1_1.cc
+// TOP-NOT: b1_2.cc
+// TOP: c0{{/|\\}}c1{{/|\\}}
+// TOP-NOT: c2_1.cc
+// TOP-NOT: b2_2.cc
+// TOP: main.cc
+
+
+// B: href={{"|'}}..{{/|\\}}index.html{{"|'}}
+// B: b1_1.cc
+// B: b1_2.cc
+
+
+// C1: href={{"|'}}..{{/|\\}}..{{/|\\}}index.html{{"|'}}
+// C1: c0{{/|\\}}c1
+// C1: c2.h
+// C1: c2_1.cc
diff --git a/llvm/tools/llvm-cov/CodeCoverage.cpp b/llvm/tools/llvm-cov/CodeCoverage.cpp
--- a/llvm/tools/llvm-cov/CodeCoverage.cpp
+++ b/llvm/tools/llvm-cov/CodeCoverage.cpp
@@ -971,6 +971,10 @@
                                    cl::desc("Show function instantiations"),
                                    cl::init(true), cl::cat(ViewCategory));
 
+  cl::opt<bool> ShowDirectoryCoverage("show-directory-coverage", cl::Optional,
+                                      cl::desc("Show directory coverage"),
+                                      cl::cat(ViewCategory));
+
   cl::opt<std::string> ShowOutputDirectory(
       "output-dir", cl::init(""),
       cl::desc("Directory in which coverage information is written out"));
@@ -1051,6 +1055,7 @@
   ViewOpts.ShowBranchPercents =
       ShowBranches == CoverageViewOptions::BranchOutputType::Percent;
   ViewOpts.ShowFunctionInstantiations = ShowInstantiations;
+  ViewOpts.ShowDirectoryCoverage = ShowDirectoryCoverage;
   ViewOpts.ShowOutputDirectory = ShowOutputDirectory;
   ViewOpts.TabSize = TabSize;
   ViewOpts.ProjectTitle = ProjectTitle;
diff --git a/llvm/tools/llvm-cov/CoverageViewOptions.h b/llvm/tools/llvm-cov/CoverageViewOptions.h
--- a/llvm/tools/llvm-cov/CoverageViewOptions.h
+++ b/llvm/tools/llvm-cov/CoverageViewOptions.h
@@ -38,6 +38,7 @@
   bool ShowBranchSummary;
   bool ShowRegionSummary;
   bool ShowInstantiationSummary;
+  bool ShowDirectoryCoverage;
   bool ExportSummaryOnly;
   bool SkipExpansions;
   bool SkipFunctions;
diff --git a/llvm/tools/llvm-cov/SourceCoverageView.h b/llvm/tools/llvm-cov/SourceCoverageView.h
--- a/llvm/tools/llvm-cov/SourceCoverageView.h
+++ b/llvm/tools/llvm-cov/SourceCoverageView.h
@@ -99,7 +99,7 @@
   CoveragePrinter(const CoverageViewOptions &Opts) : Opts(Opts) {}
 
   /// Return `OutputDir/ToplevelDir/Path.Extension`. If \p InToplevel is
-  /// false, skip the ToplevelDir component. If \p Relative is false, skip the
+  /// true, skip the ToplevelDir component. If \p Relative is true, skip the
   /// OutputDir component.
   std::string getOutputPath(StringRef Path, StringRef Extension,
                             bool InToplevel, bool Relative = true) const;
diff --git a/llvm/tools/llvm-cov/SourceCoverageView.cpp b/llvm/tools/llvm-cov/SourceCoverageView.cpp
--- a/llvm/tools/llvm-cov/SourceCoverageView.cpp
+++ b/llvm/tools/llvm-cov/SourceCoverageView.cpp
@@ -78,6 +78,8 @@
   case CoverageViewOptions::OutputFormat::Text:
     return std::make_unique<CoveragePrinterText>(Opts);
   case CoverageViewOptions::OutputFormat::HTML:
+    if (Opts.ShowDirectoryCoverage)
+      return std::make_unique<CoveragePrinterHTMLDirectory>(Opts);
     return std::make_unique<CoveragePrinterHTML>(Opts);
   case CoverageViewOptions::OutputFormat::Lcov:
     // Unreachable because CodeCoverage.cpp should terminate with an error
diff --git a/llvm/tools/llvm-cov/SourceCoverageViewHTML.h b/llvm/tools/llvm-cov/SourceCoverageViewHTML.h
--- a/llvm/tools/llvm-cov/SourceCoverageViewHTML.h
+++ b/llvm/tools/llvm-cov/SourceCoverageViewHTML.h
@@ -19,6 +19,8 @@
 
 using namespace coverage;
 
+class ThreadPool;
+
 struct FileCoverageSummary;
 
 /// A coverage printer for html output.
@@ -36,6 +38,10 @@
   CoveragePrinterHTML(const CoverageViewOptions &Opts)
       : CoveragePrinter(Opts) {}
 
+protected:
+  Error emitStyleSheet();
+  void emitBeforeTable(raw_ostream &OSRef, const std::string &Title);
+
 private:
   void emitFileSummary(raw_ostream &OS, StringRef SF,
                        const FileCoverageSummary &FCS,
@@ -44,6 +50,39 @@
                               const FileCoverageSummary &FCS) const;
 };
 
+/// A coverage printer for html output, but generates index files in every
+/// subdirectory to show a hierarchical view.
+class CoveragePrinterHTMLDirectory : public CoveragePrinterHTML {
+public:
+  using CoveragePrinterHTML::CoveragePrinterHTML;
+
+  Error createIndexFile(ArrayRef<std::string> SourceFiles,
+                        const coverage::CoverageMapping &Coverage,
+                        const CoverageFiltersMatchAll &Filters) override;
+
+private:
+  // Member variables for avoiding passing arguments repeatedly in recursive
+  // calls.
+  const coverage::CoverageMapping *CoverageNow;
+  const CoverageFiltersMatchAll *FiltersNow;
+
+  ThreadPool *PoolNow; // For calling CoverageReport::prepareSingleFileReport
+                       // asynchronously in createSubIndexFile.
+  std::vector<unsigned> LCPStack; // For calling createSubIndexFile
+                                  // recursively. [0] is root LCP length.
+
+  // Filter out files in LCP directory, group others by subdirectory and call
+  // recursively on them. The size of \p Files must be greater than 0. The
+  // FileCoverageSummary of this directory will be added to \p Totals.
+  // Current LCP is LCPStack.back().
+  Error createSubIndexFile(const ArrayRef<StringRef> &Files,
+                           FileCoverageSummary *Totals);
+
+  std::string buildTitleLinks(StringRef LCPath) const;
+
+  std::string buildRelLinkToFile(StringRef RelPath, bool IsDir) const;
+};
+
 /// A code coverage view which supports html-based rendering.
 class SourceCoverageViewHTML : public SourceCoverageView {
   void renderViewHeader(raw_ostream &OS) override;
diff --git a/llvm/tools/llvm-cov/SourceCoverageViewHTML.cpp b/llvm/tools/llvm-cov/SourceCoverageViewHTML.cpp
--- a/llvm/tools/llvm-cov/SourceCoverageViewHTML.cpp
+++ b/llvm/tools/llvm-cov/SourceCoverageViewHTML.cpp
@@ -10,12 +10,15 @@
 ///
 //===----------------------------------------------------------------------===//
 
-#include "CoverageReport.h"
 #include "SourceCoverageViewHTML.h"
+#include "CoverageReport.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Support/Format.h"
 #include "llvm/Support/Path.h"
+#include "llvm/Support/ThreadPool.h"
+#include <forward_list>
+#include <map>
 #include <optional>
 
 using namespace llvm;
@@ -65,7 +68,7 @@
 }
 
 const char *BeginHeader =
-  "<head>"
+    "<head>"
     "<meta name='viewport' content='width=device-width,initial-scale=1'>"
     "<meta charset='UTF-8'>";
 
@@ -272,11 +275,96 @@
   OS << EndHeader << "<body>";
 }
 
+void emitTableRow(raw_ostream &OS, const CoverageViewOptions &Opts,
+                  const std::string &FirstCol, const FileCoverageSummary &FCS,
+                  bool IsTotals) {
+  SmallVector<std::string, 8> Columns;
+
+  // Format a coverage triple and add the result to the list of columns.
+  auto AddCoverageTripleToColumn =
+      [&Columns, &Opts](unsigned Hit, unsigned Total, float Pctg) {
+        std::string S;
+        {
+          raw_string_ostream RSO{S};
+          if (Total)
+            RSO << format("%*.2f", 7, Pctg) << "% ";
+          else
+            RSO << "- ";
+          RSO << '(' << Hit << '/' << Total << ')';
+        }
+        const char *CellClass = "column-entry-yellow";
+        if (Pctg >= Opts.HighCovWatermark)
+          CellClass = "column-entry-green";
+        else if (Pctg < Opts.LowCovWatermark)
+          CellClass = "column-entry-red";
+        Columns.emplace_back(tag("td", tag("pre", S), CellClass));
+      };
+
+  Columns.emplace_back(tag("td", tag("pre", FirstCol)));
+  AddCoverageTripleToColumn(FCS.FunctionCoverage.getExecuted(),
+                            FCS.FunctionCoverage.getNumFunctions(),
+                            FCS.FunctionCoverage.getPercentCovered());
+  if (Opts.ShowInstantiationSummary)
+    AddCoverageTripleToColumn(FCS.InstantiationCoverage.getExecuted(),
+                              FCS.InstantiationCoverage.getNumFunctions(),
+                              FCS.InstantiationCoverage.getPercentCovered());
+  AddCoverageTripleToColumn(FCS.LineCoverage.getCovered(),
+                            FCS.LineCoverage.getNumLines(),
+                            FCS.LineCoverage.getPercentCovered());
+  if (Opts.ShowRegionSummary)
+    AddCoverageTripleToColumn(FCS.RegionCoverage.getCovered(),
+                              FCS.RegionCoverage.getNumRegions(),
+                              FCS.RegionCoverage.getPercentCovered());
+  if (Opts.ShowBranchSummary)
+    AddCoverageTripleToColumn(FCS.BranchCoverage.getCovered(),
+                              FCS.BranchCoverage.getNumBranches(),
+                              FCS.BranchCoverage.getPercentCovered());
+
+  if (IsTotals)
+    OS << tag("tr", join(Columns.begin(), Columns.end(), ""), "light-row-bold");
+  else
+    OS << tag("tr", join(Columns.begin(), Columns.end(), ""), "light-row");
+}
+
 void emitEpilog(raw_ostream &OS) {
   OS << "</body>"
      << "</html>";
 }
 
+/// Determine the length of the longest redundant prefix of the substrs starts
+/// from \p LCP in \p Paths. \p Paths can't be empty. If there's only one path
+/// in \p Paths, the length of the path is returned. Note this is differnet from
+/// the behavior for the function of the same name in CoverageReport.cpp .
+unsigned getRedundantPrefixLen(ArrayRef<StringRef> Paths, unsigned LCP = 0) {
+  assert(!Paths.empty() && "Paths must have at least one element");
+
+  auto Iter = Paths.begin();
+  auto IterE = Paths.end();
+  auto First = Iter->substr(LCP);
+  SmallVector<StringRef, 16> CommonComponents{sys::path::begin(First),
+                                              sys::path::end(First)};
+  unsigned Len = First.size() - LCP;
+  while (++Iter != IterE) {
+    auto Substr = Iter->substr(LCP);
+    auto I = sys::path::begin(Substr);
+    auto E = sys::path::end(Substr);
+
+    unsigned Index = 0;
+    while (I != E) {
+      if (Index >= CommonComponents.size())
+        break;
+      if (CommonComponents[Index] != *I) {
+        CommonComponents.resize(Index);
+        Len = I - sys::path::begin(Substr);
+        break;
+      }
+      ++Index, ++I;
+    }
+  }
+
+  return Len;
+}
+
 } // anonymous namespace
 
 Expected<CoveragePrinter::OwnedStream>
@@ -330,33 +418,44 @@
   return a(LinkTarget, LinkText);
 }
 
+Error CoveragePrinterHTML::emitStyleSheet() {
+  auto CSSOrErr = createOutputStream("style", "css", /*InToplevel=*/true);
+  if (Error E = CSSOrErr.takeError())
+    return E;
+
+  OwnedStream CSS = std::move(CSSOrErr.get());
+  CSS->operator<<(CSSForCoverage);
+
+  return Error::success();
+}
+
+void CoveragePrinterHTML::emitBeforeTable(raw_ostream &OSRef,
+                                          const std::string &Title) {
+  // Emit some basic information about the coverage report.
+  if (Opts.hasProjectTitle())
+    OSRef << tag(ProjectTitleTag, escape(Opts.ProjectTitle, Opts));
+  OSRef << tag(ReportTitleTag, Title);
+  if (Opts.hasCreatedTime())
+    OSRef << tag(CreatedTimeTag, escape(Opts.CreatedTimeStr, Opts));
+
+  // Emit a link to some documentation.
+  OSRef << tag("p", "Click " +
+                        a("http://clang.llvm.org/docs/"
+                          "SourceBasedCodeCoverage.html#interpreting-reports",
+                          "here") +
+                        " for information about interpreting this report.");
+
+  // Emit a table containing links to reports for each file in the covmapping.
+  // Exclude files which don't contain any regions.
+  OSRef << BeginCenteredDiv << BeginTable;
+  emitColumnLabelsForIndex(OSRef, Opts);
+}
+
 /// Render a file coverage summary (\p FCS) in a table row. If \p IsTotals is
 /// false, link the summary to \p SF.
 void CoveragePrinterHTML::emitFileSummary(raw_ostream &OS, StringRef SF,
                                           const FileCoverageSummary &FCS,
                                           bool IsTotals) const {
-  SmallVector<std::string, 8> Columns;
-
-  // Format a coverage triple and add the result to the list of columns.
-  auto AddCoverageTripleToColumn =
-      [&Columns, this](unsigned Hit, unsigned Total, float Pctg) {
-        std::string S;
-        {
-          raw_string_ostream RSO{S};
-          if (Total)
-            RSO << format("%*.2f", 7, Pctg) << "% ";
-          else
-            RSO << "- ";
-          RSO << '(' << Hit << '/' << Total << ')';
-        }
-        const char *CellClass = "column-entry-yellow";
-        if (Pctg >= Opts.HighCovWatermark)
-          CellClass = "column-entry-green";
-        else if (Pctg < Opts.LowCovWatermark)
-          CellClass = "column-entry-red";
-        Columns.emplace_back(tag("td", tag("pre", S), CellClass));
-      };
-
   // Simplify the display file path, and wrap it in a link if requested.
   std::string Filename;
   if (IsTotals) {
@@ -365,43 +464,16 @@
     Filename = buildLinkToFile(SF, FCS);
   }
 
-  Columns.emplace_back(tag("td", tag("pre", Filename)));
-  AddCoverageTripleToColumn(FCS.FunctionCoverage.getExecuted(),
-                            FCS.FunctionCoverage.getNumFunctions(),
-                            FCS.FunctionCoverage.getPercentCovered());
-  if (Opts.ShowInstantiationSummary)
-    AddCoverageTripleToColumn(FCS.InstantiationCoverage.getExecuted(),
-                              FCS.InstantiationCoverage.getNumFunctions(),
-                              FCS.InstantiationCoverage.getPercentCovered());
-  AddCoverageTripleToColumn(FCS.LineCoverage.getCovered(),
-                            FCS.LineCoverage.getNumLines(),
-                            FCS.LineCoverage.getPercentCovered());
-  if (Opts.ShowRegionSummary)
-    AddCoverageTripleToColumn(FCS.RegionCoverage.getCovered(),
-                              FCS.RegionCoverage.getNumRegions(),
-                              FCS.RegionCoverage.getPercentCovered());
-  if (Opts.ShowBranchSummary)
-    AddCoverageTripleToColumn(FCS.BranchCoverage.getCovered(),
-                              FCS.BranchCoverage.getNumBranches(),
-                              FCS.BranchCoverage.getPercentCovered());
-
-  if (IsTotals)
-    OS << tag("tr", join(Columns.begin(), Columns.end(), ""), "light-row-bold");
-  else
-    OS << tag("tr", join(Columns.begin(), Columns.end(), ""), "light-row");
+  emitTableRow(OS, Opts, Filename, FCS, IsTotals);
 }
 
 Error CoveragePrinterHTML::createIndexFile(
     ArrayRef<std::string> SourceFiles, const CoverageMapping &Coverage,
     const CoverageFiltersMatchAll &Filters) {
   // Emit the default stylesheet.
-  auto CSSOrErr = createOutputStream("style", "css", /*InToplevel=*/true);
-  if (Error E = CSSOrErr.takeError())
+  if (Error E = emitStyleSheet())
     return E;
 
-  OwnedStream CSS = std::move(CSSOrErr.get());
-  CSS->operator<<(CSSForCoverage);
-
   // Emit a file index along with some coverage statistics.
   auto OSOrErr = createOutputStream("index", "html", /*InToplevel=*/true);
   if (Error E = OSOrErr.takeError())
@@ -412,24 +484,8 @@
   assert(Opts.hasOutputDirectory() && "No output directory for index file");
   emitPrelude(OSRef, Opts, getPathToStyle(""));
 
-  // Emit some basic information about the coverage report.
-  if (Opts.hasProjectTitle())
-    OSRef << tag(ProjectTitleTag, escape(Opts.ProjectTitle, Opts));
-  OSRef << tag(ReportTitleTag, "Coverage Report");
-  if (Opts.hasCreatedTime())
-    OSRef << tag(CreatedTimeTag, escape(Opts.CreatedTimeStr, Opts));
+  emitBeforeTable(OSRef, "Coverage Report");
 
-  // Emit a link to some documentation.
-  OSRef << tag("p", "Click " +
-                        a("http://clang.llvm.org/docs/"
-                          "SourceBasedCodeCoverage.html#interpreting-reports",
-                          "here") +
-                        " for information about interpreting this report.");
-
-  // Emit a table containing links to reports for each file in the covmapping.
-  // Exclude files which don't contain any regions.
-  OSRef << BeginCenteredDiv << BeginTable;
-  emitColumnLabelsForIndex(OSRef, Opts);
   FileCoverageSummary Totals("TOTALS");
   auto FileReports = CoverageReport::prepareFileReports(
       Coverage, Totals, SourceFiles, Opts, Filters);
@@ -465,6 +521,232 @@
   return Error::success();
 }
 
+Error CoveragePrinterHTMLDirectory::createIndexFile(
+    ArrayRef<std::string> SourceFiles, const CoverageMapping &Coverage,
+    const CoverageFiltersMatchAll &Filters) {
+  // The createSubIndexFile function only works when SourceFiles is
+  // not empty. So we fallback to CoveragePrinterHTML when it is.
+  if (SourceFiles.empty())
+    return CoveragePrinterHTML::createIndexFile(SourceFiles, Coverage, Filters);
+
+  // Emit the default stylesheet.
+  if (Error E = emitStyleSheet())
+    return E;
+
+  // Emit index files in every subdirectory.
+  std::vector<StringRef> Files(SourceFiles.begin(), SourceFiles.end());
+  ThreadPoolStrategy PoolS = hardware_concurrency(Opts.NumThreads);
+  if (Opts.NumThreads == 0) {
+    PoolS = heavyweight_hardware_concurrency(Files.size());
+    PoolS.Limit = true;
+  }
+  ThreadPool Pool(PoolS); // The above initialization code was copied from
+                          // CoverageReport::prepareFileReports.
+
+  unsigned RootLCP;
+  if (SourceFiles.size() == 1)
+    RootLCP = sys::path::parent_path(SourceFiles.front()).size() + 1;
+  // We handle this case specially. If there's only one file in total,
+  // its parent directory is considered as the LCP.
+  else
+    RootLCP = getRedundantPrefixLen(Files);
+  auto LCPath = SourceFiles.front().substr(0, RootLCP);
+
+  CoverageNow = &Coverage;
+  FiltersNow = &Filters;
+  PoolNow = &Pool;
+  LCPStack = {RootLCP};
+  FileCoverageSummary RootTotal({}); // The root total is useless and ignored.
+  if (auto E = createSubIndexFile(Files, &RootTotal))
+    return E;
+
+  // Emit the top level index file. Top level index file is just a redirection
+  // to the index file in the LCP directory.
+  auto OSOrErr = createOutputStream("index", "html", /*InToplevel=*/true);
+  if (auto E = OSOrErr.takeError())
+    return E;
+  auto OS = std::move(OSOrErr.get());
+  auto LCPIndexFilePath =
+      getOutputPath(LCPath + "index", "html", /*InToplevel=*/false);
+  *OS.get() << R"(<!DOCTYPE html>
+  <html>
+    <head>
+      <meta http-equiv="Refresh" content="0; url=')"
+            << LCPIndexFilePath << R"('" />
+    </head>
+    <body></body>
+  </html>
+  )";
+
+  return Error::success();
+}
+
+Error CoveragePrinterHTMLDirectory::createSubIndexFile(
+    const ArrayRef<StringRef> &Files, FileCoverageSummary *Totals) {
+  assert(!Files.empty() && "Only works when Files is not empty");
+  auto LCP = LCPStack.back();
+  auto LCPath = Files.front().substr(0, LCP).str();
+  assert(LCPath.back() == '/' && "LCPath should end with a slash");
+  auto OSOrErr =
+      createOutputStream(LCPath + "index", "html", /*InToplevel=*/false);
+  if (auto E = OSOrErr.takeError())
+    return E;
+  auto OS = std::move(OSOrErr.get());
+  raw_ostream &OSRef = *OS.get();
+
+  assert(Opts.hasOutputDirectory() && "No output directory for index file");
+  auto IndexHtmlPath =
+      getOutputPath(LCPath + "index", "html", /*InToplevel=*/false);
+  emitPrelude(OSRef, Opts, getPathToStyle(IndexHtmlPath));
+
+  auto NavLink = buildTitleLinks(LCPath);
+  emitBeforeTable(OSRef, "Coverage Report (" + NavLink + ")");
+
+  // Filter out files in current directory and group others by subdiretory.
+  // std::map is used to keep entries in order.
+  std::map<StringRef, FileCoverageSummary> CurrentFiles;
+  std::map<StringRef, std::vector<StringRef>> CurrentDirs;
+  for (auto &&File : Files) {
+    auto SubPath = File.substr(LCPath.size());
+
+    auto I = sys::path::begin(SubPath);
+    auto E = sys::path::end(SubPath);
+    assert(I != E && "Such case should have been filtered out in the caller");
+
+    auto Name = *I;
+    if (++I == E) {
+      auto Iter = CurrentFiles.emplace(Name, File).first;
+      PoolNow->async(&CoverageReport::prepareSingleFileReport, File,
+                     CoverageNow, Opts, LCP, &Iter->second, FiltersNow);
+    }
+
+    else
+      CurrentDirs[Name].push_back(File);
+  }
+
+  // Emit subdirectories first to make them at the top of the table.
+  FileCoverageSummary CurrentTotals(LCPath);
+  for (auto &&Dir : CurrentDirs) {
+    if (Dir.second.size() == 1) {
+      // If there's only one file in that subdirectory, we don't bother to
+      // create index file for it. Instead, we show the file report directly at
+      // this level.
+      auto RelPath = Dir.second.front().substr(LCP);
+      FileCoverageSummary FCS(RelPath);
+      CoverageReport::prepareSingleFileReport(Dir.second[0], CoverageNow, Opts,
+                                              LCP, &FCS, FiltersNow);
+      emitTableRow(OSRef, Opts, buildRelLinkToFile(RelPath, /*IsDir=*/false),
+                   FCS, /*IsTotals=*/false);
+      CurrentTotals += FCS;
+    } else {
+      auto SubDirLCP = getRedundantPrefixLen(Dir.second, LCP);
+      auto RelPath = Dir.second.front().substr(LCP, SubDirLCP);
+      FileCoverageSummary FCS(RelPath);
+      LCPStack.push_back(LCP + SubDirLCP);
+      if (auto E = createSubIndexFile(Dir.second, &FCS))
+        return E;
+      emitTableRow(OSRef, Opts, buildRelLinkToFile(RelPath, /*IsDir=*/true),
+                   FCS, /*IsTotals=*/false);
+      CurrentTotals += FCS;
+    }
+  }
+
+  // Then emit the files in current directory.
+  PoolNow->wait(); // Makes files reporting overlap with subdir reporting.
+  std::vector<decltype(CurrentFiles)::const_iterator> EmptyFiles;
+  for (auto I = CurrentFiles.begin(), E = CurrentFiles.end(); I != E; ++I) {
+    if (I->second.FunctionCoverage.getNumFunctions())
+      emitTableRow(OSRef, Opts, buildRelLinkToFile(I->first, /*IsDir=*/false),
+                   I->second, /*IsTotals=*/false);
+    else
+      EmptyFiles.push_back(I);
+    CurrentTotals += I->second;
+  }
+
+  // Emit the totals row.
+  emitTableRow(OSRef, Opts, "Totals", CurrentTotals, /*IsTotals=*/false);
+  OSRef << EndTable << EndCenteredDiv;
+
+  // Emit links to files which don't contain any functions. These are normally
+  // not very useful, but could be relevant for code which abuses the
+  // preprocessor.
+  if (!EmptyFiles.empty() && FiltersNow->empty()) {
+    OSRef << tag("p", "Files which contain no functions. (These "
+                      "files contain code pulled into other files "
+                      "by the preprocessor.)\n");
+    OSRef << BeginCenteredDiv << BeginTable;
+    for (auto I : EmptyFiles) {
+      auto Link = buildRelLinkToFile(I->first, /*IsDir=*/false);
+      OSRef << tag("tr", tag("td", tag("pre", Link)), "light-row") << '\n';
+    }
+    OSRef << EndTable << EndCenteredDiv;
+  }
+
+  // Emit epilog.
+  OSRef << tag("h5", escape(Opts.getLLVMVersionString(), Opts));
+  emitEpilog(OSRef);
+
+  *Totals += CurrentTotals;
+  LCPStack.pop_back();
+  return Error::success();
+}
+
+std::string
+CoveragePrinterHTMLDirectory::buildTitleLinks(StringRef LCPath) const {
+  SmallVector<std::pair<std::string, unsigned>, 16> Components;
+  auto Iter = LCPStack.begin(), IterE = LCPStack.end();
+  if (*Iter > 0)
+    Components.push_back({
+        LCPath.substr(0, *Iter - 1).str(), // Remove trailing slash.
+        0,
+    });
+  for (auto Last = *Iter; ++Iter != IterE; Last = *Iter) {
+    auto SubPath = LCPath.substr(Last, *Iter - Last - 1);
+    auto Level = unsigned(SubPath.count(sys::path::get_separator())) + 1;
+    Components.back().second += Level;
+    Components.push_back({SubPath.str(), Level});
+  }
+
+  std::string S;
+  for (auto I = Components.begin(), E = Components.end();;) {
+    auto &Name = I->first;
+    if (++I == E) {
+      S += a("./index.html", Name);
+      S += sys::path::get_separator();
+      break;
+    }
+
+    std::string Link;
+    for (unsigned J = I->second; J > 0; --J) {
+      Link += "..";
+      Link += sys::path::get_separator();
+    }
+    Link += "index.html";
+    S += a(Link, Name);
+    S += sys::path::get_separator();
+  }
+  return S;
+}
+
+std::string CoveragePrinterHTMLDirectory::buildRelLinkToFile(StringRef RelPath,
+                                                             bool IsDir) const {
+  SmallString<128> LinkTextStr(RelPath);
+  sys::path::remove_dots(LinkTextStr, /*remove_dot_dot=*/true);
+  sys::path::native(LinkTextStr);
+
+  std::string LinkTargetStr;
+  if (IsDir) {
+    LinkTextStr += sys::path::get_separator();
+    LinkTargetStr = (RelPath + "index.html").str();
+  } else {
+    LinkTargetStr = (RelPath + ".html").str();
+  }
+
+  auto LinkText = escape(LinkTextStr, Opts);
+  auto LinkTarget = escape(LinkTargetStr, Opts);
+  return a(LinkTarget, LinkText);
+}
+
 void SourceCoverageViewHTML::renderViewHeader(raw_ostream &OS) {
   OS << BeginCenteredDiv << BeginTable;
 }
diff --git a/llvm/utils/prepare-code-coverage-artifact.py b/llvm/utils/prepare-code-coverage-artifact.py
--- a/llvm/utils/prepare-code-coverage-artifact.py
+++ b/llvm/utils/prepare-code-coverage-artifact.py
@@ -67,6 +67,7 @@
             "-o",
             report_dir,
             "-show-line-counts-or-regions",
+            "-show-directory-coverage",
             "-Xdemangler",
             "c++filt",
             "-Xdemangler",