[llvm-cov] Add support for baseline coverage (#117910)

When no profile is provided, but the new --empty-profile option is
specifed, the export/report/show commands now emit coverage data
equivalent to that obtained from a profile with all zero counters
("baseline coverage").

This is useful for build systems (e.g. Bazel) that can track coverage
information for each build target, even those that are never linked into
tests and thus don't have runtime coverage data recorded. By merging in
baseline coverage, lines in files that aren't linked into tests are
correctly reported as uncovered.

1 files changed, 75 insertions, 48 deletions

diff --git a/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp b/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
index dd74eb0..429ec5c 100644
--- a/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
+++ b/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
@@ -823,7 +823,8 @@ public:
 
 Error CoverageMapping::loadFunctionRecord(
     const CoverageMappingRecord &Record,
-    IndexedInstrProfReader &ProfileReader) {
+    const std::optional<std::reference_wrapper<IndexedInstrProfReader>>
+        &ProfileReader) {
   StringRef OrigFuncName = Record.FunctionName;
   if (OrigFuncName.empty())
     return make_error<CoverageMapError>(coveragemap_error::malformed,
@@ -837,35 +838,44 @@ Error CoverageMapping::loadFunctionRecord(
   CounterMappingContext Ctx(Record.Expressions);
 
   std::vector<uint64_t> Counts;
-  if (Error E = ProfileReader.getFunctionCounts(Record.FunctionName,
-                                                Record.FunctionHash, Counts)) {
-    instrprof_error IPE = std::get<0>(InstrProfError::take(std::move(E)));
-    if (IPE == instrprof_error::hash_mismatch) {
-      FuncHashMismatches.emplace_back(std::string(Record.FunctionName),
-                                      Record.FunctionHash);
-      return Error::success();
+  if (ProfileReader) {
+    if (Error E = ProfileReader.value().get().getFunctionCounts(
+            Record.FunctionName, Record.FunctionHash, Counts)) {
+      instrprof_error IPE = std::get<0>(InstrProfError::take(std::move(E)));
+      if (IPE == instrprof_error::hash_mismatch) {
+        FuncHashMismatches.emplace_back(std::string(Record.FunctionName),
+                                        Record.FunctionHash);
+        return Error::success();
+      }
+      if (IPE != instrprof_error::unknown_function)
+        return make_error<InstrProfError>(IPE);
+      Counts.assign(getMaxCounterID(Ctx, Record) + 1, 0);
     }
-    if (IPE != instrprof_error::unknown_function)
-      return make_error<InstrProfError>(IPE);
+  } else {
     Counts.assign(getMaxCounterID(Ctx, Record) + 1, 0);
   }
   Ctx.setCounts(Counts);
 
   bool IsVersion11 =
-      ProfileReader.getVersion() < IndexedInstrProf::ProfVersion::Version12;
+      ProfileReader && ProfileReader.value().get().getVersion() <
+                           IndexedInstrProf::ProfVersion::Version12;
 
   BitVector Bitmap;
-  if (Error E = ProfileReader.getFunctionBitmap(Record.FunctionName,
-                                                Record.FunctionHash, Bitmap)) {
-    instrprof_error IPE = std::get<0>(InstrProfError::take(std::move(E)));
-    if (IPE == instrprof_error::hash_mismatch) {
-      FuncHashMismatches.emplace_back(std::string(Record.FunctionName),
-                                      Record.FunctionHash);
-      return Error::success();
+  if (ProfileReader) {
+    if (Error E = ProfileReader.value().get().getFunctionBitmap(
+            Record.FunctionName, Record.FunctionHash, Bitmap)) {
+      instrprof_error IPE = std::get<0>(InstrProfError::take(std::move(E)));
+      if (IPE == instrprof_error::hash_mismatch) {
+        FuncHashMismatches.emplace_back(std::string(Record.FunctionName),
+                                        Record.FunctionHash);
+        return Error::success();
+      }
+      if (IPE != instrprof_error::unknown_function)
+        return make_error<InstrProfError>(IPE);
+      Bitmap = BitVector(getMaxBitmapSize(Record, IsVersion11));
     }
-    if (IPE != instrprof_error::unknown_function)
-      return make_error<InstrProfError>(IPE);
-    Bitmap = BitVector(getMaxBitmapSize(Record, IsVersion11));
+  } else {
+    Bitmap = BitVector(getMaxBitmapSize(Record, false));
   }
   Ctx.setBitmap(std::move(Bitmap));
 
@@ -959,10 +969,14 @@ Error CoverageMapping::loadFunctionRecord(
 // of CoverageMappingReader instances.
 Error CoverageMapping::loadFromReaders(
     ArrayRef<std::unique_ptr<CoverageMappingReader>> CoverageReaders,
-    IndexedInstrProfReader &ProfileReader, CoverageMapping &Coverage) {
-  assert(!Coverage.SingleByteCoverage ||
-         *Coverage.SingleByteCoverage == ProfileReader.hasSingleByteCoverage());
-  Coverage.SingleByteCoverage = ProfileReader.hasSingleByteCoverage();
+    std::optional<std::reference_wrapper<IndexedInstrProfReader>>
+        &ProfileReader,
+    CoverageMapping &Coverage) {
+  assert(!Coverage.SingleByteCoverage || !ProfileReader ||
+         *Coverage.SingleByteCoverage ==
+             ProfileReader.value().get().hasSingleByteCoverage());
+  Coverage.SingleByteCoverage =
+      !ProfileReader || ProfileReader.value().get().hasSingleByteCoverage();
   for (const auto &CoverageReader : CoverageReaders) {
     for (auto RecordOrErr : *CoverageReader) {
       if (Error E = RecordOrErr.takeError())
@@ -977,7 +991,8 @@ Error CoverageMapping::loadFromReaders(
 
 Expected<std::unique_ptr<CoverageMapping>> CoverageMapping::load(
     ArrayRef<std::unique_ptr<CoverageMappingReader>> CoverageReaders,
-    IndexedInstrProfReader &ProfileReader) {
+    std::optional<std::reference_wrapper<IndexedInstrProfReader>>
+        &ProfileReader) {
   auto Coverage = std::unique_ptr<CoverageMapping>(new CoverageMapping());
   if (Error E = loadFromReaders(CoverageReaders, ProfileReader, *Coverage))
     return std::move(E);
@@ -986,18 +1001,19 @@ Expected<std::unique_ptr<CoverageMapping>> CoverageMapping::load(
 
 // If E is a no_data_found error, returns success. Otherwise returns E.
 static Error handleMaybeNoDataFoundError(Error E) {
-  return handleErrors(
-      std::move(E), [](const CoverageMapError &CME) {
-        if (CME.get() == coveragemap_error::no_data_found)
-          return static_cast<Error>(Error::success());
-        return make_error<CoverageMapError>(CME.get(), CME.getMessage());
-      });
+  return handleErrors(std::move(E), [](const CoverageMapError &CME) {
+    if (CME.get() == coveragemap_error::no_data_found)
+      return static_cast<Error>(Error::success());
+    return make_error<CoverageMapError>(CME.get(), CME.getMessage());
+  });
 }
 
 Error CoverageMapping::loadFromFile(
     StringRef Filename, StringRef Arch, StringRef CompilationDir,
-    IndexedInstrProfReader &ProfileReader, CoverageMapping &Coverage,
-    bool &DataFound, SmallVectorImpl<object::BuildID> *FoundBinaryIDs) {
+    std::optional<std::reference_wrapper<IndexedInstrProfReader>>
+        &ProfileReader,
+    CoverageMapping &Coverage, bool &DataFound,
+    SmallVectorImpl<object::BuildID> *FoundBinaryIDs) {
   auto CovMappingBufOrErr = MemoryBuffer::getFileOrSTDIN(
       Filename, /*IsText=*/false, /*RequiresNullTerminator=*/false);
   if (std::error_code EC = CovMappingBufOrErr.getError())
@@ -1033,13 +1049,23 @@ Error CoverageMapping::loadFromFile(
 }
 
 Expected<std::unique_ptr<CoverageMapping>> CoverageMapping::load(
-    ArrayRef<StringRef> ObjectFilenames, StringRef ProfileFilename,
-    vfs::FileSystem &FS, ArrayRef<StringRef> Arches, StringRef CompilationDir,
+    ArrayRef<StringRef> ObjectFilenames,
+    std::optional<StringRef> ProfileFilename, vfs::FileSystem &FS,
+    ArrayRef<StringRef> Arches, StringRef CompilationDir,
     const object::BuildIDFetcher *BIDFetcher, bool CheckBinaryIDs) {
-  auto ProfileReaderOrErr = IndexedInstrProfReader::create(ProfileFilename, FS);
-  if (Error E = ProfileReaderOrErr.takeError())
-    return createFileError(ProfileFilename, std::move(E));
-  auto ProfileReader = std::move(ProfileReaderOrErr.get());
+  std::unique_ptr<IndexedInstrProfReader> ProfileReader;
+  if (ProfileFilename) {
+    auto ProfileReaderOrErr =
+        IndexedInstrProfReader::create(ProfileFilename.value(), FS);
+    if (Error E = ProfileReaderOrErr.takeError())
+      return createFileError(ProfileFilename.value(), std::move(E));
+    ProfileReader = std::move(ProfileReaderOrErr.get());
+  }
+  auto ProfileReaderRef =
+      ProfileReader
+          ? std::optional<std::reference_wrapper<IndexedInstrProfReader>>(
+                *ProfileReader)
+          : std::nullopt;
   auto Coverage = std::unique_ptr<CoverageMapping>(new CoverageMapping());
   bool DataFound = false;
 
@@ -1053,16 +1079,17 @@ Expected<std::unique_ptr<CoverageMapping>> CoverageMapping::load(
 
   SmallVector<object::BuildID> FoundBinaryIDs;
   for (const auto &File : llvm::enumerate(ObjectFilenames)) {
-    if (Error E =
-            loadFromFile(File.value(), GetArch(File.index()), CompilationDir,
-                         *ProfileReader, *Coverage, DataFound, &FoundBinaryIDs))
+    if (Error E = loadFromFile(File.value(), GetArch(File.index()),
+                               CompilationDir, ProfileReaderRef, *Coverage,
+                               DataFound, &FoundBinaryIDs))
       return std::move(E);
   }
 
   if (BIDFetcher) {
     std::vector<object::BuildID> ProfileBinaryIDs;
-    if (Error E = ProfileReader->readBinaryIds(ProfileBinaryIDs))
-      return createFileError(ProfileFilename, std::move(E));
+    if (ProfileReader)
+      if (Error E = ProfileReader->readBinaryIds(ProfileBinaryIDs))
+        return createFileError(ProfileFilename.value(), std::move(E));
 
     SmallVector<object::BuildIDRef> BinaryIDsToFetch;
     if (!ProfileBinaryIDs.empty()) {
@@ -1082,12 +1109,12 @@ Expected<std::unique_ptr<CoverageMapping>> CoverageMapping::load(
       if (PathOpt) {
         std::string Path = std::move(*PathOpt);
         StringRef Arch = Arches.size() == 1 ? Arches.front() : StringRef();
-        if (Error E = loadFromFile(Path, Arch, CompilationDir, *ProfileReader,
-                                  *Coverage, DataFound))
+        if (Error E = loadFromFile(Path, Arch, CompilationDir, ProfileReaderRef,
+                                   *Coverage, DataFound))
           return std::move(E);
       } else if (CheckBinaryIDs) {
         return createFileError(
-            ProfileFilename,
+            ProfileFilename.value(),
             createStringError(errc::no_such_file_or_directory,
                               "Missing binary ID: " +
                                   llvm::toHex(BinaryID, /*LowerCase=*/true)));