[Coverage] Store compilation dir separately in coverage mapping

We currently always store absolute filenames in coverage mapping.  This
is problematic for several reasons. It poses a problem for distributed
compilation as source location might vary across machines.  We are also
duplicating the path prefix potentially wasting space.

This change modifies how we store filenames in coverage mapping. Rather
than absolute paths, it stores the compilation directory and file paths
as given to the compiler, either relative or absolute. Later when
reading the coverage mapping information, we recombine relative paths
with the working directory. This approach is similar to handling
ofDW_AT_comp_dir in DWARF.

Finally, we also provide a new option, -fprofile-compilation-dir akin
to -fdebug-compilation-dir which can be used to manually override the
compilation directory which is useful in distributed compilation cases.

Differential Revision: https://reviews.llvm.org/D95753

1 files changed, 18 insertions, 12 deletions

diff --git a/clang/lib/CodeGen/CoverageMappingGen.cpp b/clang/lib/CodeGen/CoverageMappingGen.cpp
index ce2cb38..ebbd6aa 100644
--- a/clang/lib/CodeGen/CoverageMappingGen.cpp
+++ b/clang/lib/CodeGen/CoverageMappingGen.cpp
@@ -1606,9 +1606,17 @@ CoverageMappingModuleGen::CoverageMappingModuleGen(
   ProfilePrefixMap = CGM.getCodeGenOpts().ProfilePrefixMap;
 }
 
+std::string CoverageMappingModuleGen::getCurrentDirname() {
+  if (!CGM.getCodeGenOpts().ProfileCompilationDir.empty())
+    return CGM.getCodeGenOpts().ProfileCompilationDir;
+
+  SmallString<256> CWD;
+  llvm::sys::fs::current_path(CWD);
+  return CWD.str().str();
+}
+
 std::string CoverageMappingModuleGen::normalizeFilename(StringRef Filename) {
   llvm::SmallString<256> Path(Filename);
-  llvm::sys::fs::make_absolute(Path);
   llvm::sys::path::remove_dots(Path, /*remove_dot_dot=*/true);
   for (const auto &Entry : ProfilePrefixMap) {
     if (llvm::sys::path::replace_path_prefix(Path, Entry.first, Entry.second))
@@ -1689,18 +1697,17 @@ void CoverageMappingModuleGen::addFunctionMappingRecord(
     // also processed by the CoverageMappingWriter which performs
     // additional minimization operations such as reducing the number of
     // expressions.
+    llvm::SmallVector<std::string, 16> FilenameStrs;
     std::vector<StringRef> Filenames;
     std::vector<CounterExpression> Expressions;
     std::vector<CounterMappingRegion> Regions;
-    llvm::SmallVector<std::string, 16> FilenameStrs;
-    llvm::SmallVector<StringRef, 16> FilenameRefs;
-    FilenameStrs.resize(FileEntries.size());
-    FilenameRefs.resize(FileEntries.size());
+    FilenameStrs.resize(FileEntries.size() + 1);
+    FilenameStrs[0] = normalizeFilename(getCurrentDirname());
     for (const auto &Entry : FileEntries) {
       auto I = Entry.second;
       FilenameStrs[I] = normalizeFilename(Entry.first->getName());
-      FilenameRefs[I] = FilenameStrs[I];
     }
+    ArrayRef<std::string> FilenameRefs = llvm::makeArrayRef(FilenameStrs);
     RawCoverageMappingReader Reader(CoverageMapping, FilenameRefs, Filenames,
                                     Expressions, Regions);
     if (Reader.read())
@@ -1717,19 +1724,18 @@ void CoverageMappingModuleGen::emit() {
 
   // Create the filenames and merge them with coverage mappings
   llvm::SmallVector<std::string, 16> FilenameStrs;
-  llvm::SmallVector<StringRef, 16> FilenameRefs;
-  FilenameStrs.resize(FileEntries.size());
-  FilenameRefs.resize(FileEntries.size());
+  FilenameStrs.resize(FileEntries.size() + 1);
+  // The first filename is the current working directory.
+  FilenameStrs[0] = getCurrentDirname();
   for (const auto &Entry : FileEntries) {
     auto I = Entry.second;
     FilenameStrs[I] = normalizeFilename(Entry.first->getName());
-    FilenameRefs[I] = FilenameStrs[I];
   }
 
   std::string Filenames;
   {
     llvm::raw_string_ostream OS(Filenames);
-    CoverageFilenamesSectionWriter(FilenameRefs).write(OS);
+    CoverageFilenamesSectionWriter(FilenameStrs).write(OS);
   }
   auto *FilenamesVal =
       llvm::ConstantDataArray::getString(Ctx, Filenames, false);
@@ -1787,7 +1793,7 @@ unsigned CoverageMappingModuleGen::getFileID(const FileEntry *File) {
   auto It = FileEntries.find(File);
   if (It != FileEntries.end())
     return It->second;
-  unsigned FileID = FileEntries.size();
+  unsigned FileID = FileEntries.size() + 1;
   FileEntries.insert(std::make_pair(File, FileID));
   return FileID;
 }