[llvm-cov] Skip unnecessary coverage computations for "export -summary-only".

[Dor1s]

Summary

This speeds up export "summary-only" execution by an order of magnitude or two,
depending on number of threads used for prepareFileReports execution.

Also includes minor refactoring for splitting render of summary and detailed data
in two independent methods.

[Dor1s]

Refactor methods for file rendering

[Dor1s]

Clean up the code

[vsk]

Looks good, thanks!

tools/llvm-cov/CoverageExporterJson.h

class CoverageExporterJson : public CoverageExporter {
   void renderFunctions(
       const iterator_range<coverage::FunctionRecordIterator> &Functions);
 
   /// \brief Render an array of all the source files, also pass back a Summary.
   void renderFiles(ArrayRef<std::string> SourceFiles,
                    ArrayRef<FileCoverageSummary> FileReports);
 
   /// \brief Render a single file.
-  void renderFile(const coverage::CoverageData &FileCoverage,
+  void renderFile(const std::string &Filename,
+                  const FileCoverageSummary &FileReport);
+
+  /// \brief Render summary for a single file.
+  void renderFileCoverage(const coverage::CoverageData &FileCoverage,
                           const FileCoverageSummary &FileReport);
 
   /// \brief Render a CoverageSegment.
   void renderSegment(const coverage::CoverageSegment &Segment);
 
   /// \brief Render an ExpansionRecord.
   void renderExpansion(const coverage::ExpansionRecord &Expansion);
 
   /// \brief Render a list of CountedRegions.

tools/llvm-cov/CoverageExporterJson.cpp

 
 void CoverageExporterJson::renderFiles(
     ArrayRef<std::string> SourceFiles,
     ArrayRef<FileCoverageSummary> FileReports) {
   // Start List of Files.
   emitArrayStart();
 
   for (unsigned I = 0, E = SourceFiles.size(); I < E; ++I) {
-    // Render the file.
-    auto FileCoverage = Coverage.getCoverageForFile(SourceFiles[I]);
-    renderFile(FileCoverage, FileReports[I]);
+    renderFile(SourceFiles[I], FileReports[I]);
   }
 
   // End List of Files.
   emitArrayEnd();
 }
 
-void CoverageExporterJson::renderFile(
-    const coverage::CoverageData &FileCoverage,
+void CoverageExporterJson::renderFile(const std::string &Filename,
                                       const FileCoverageSummary &FileReport) {
    // Start File.
   emitDictStart();
 
-  emitDictElement("filename", FileCoverage.getFilename());
+  emitDictElement("filename", Filename);
   
-  // Skip segments and expansions for summary-only export mode.
   if (!Options.ExportSummaryOnly) {
-    emitDictKey("segments");
+    // Calculate and render detailed coverage information for given file.
+    auto FileCoverage = Coverage.getCoverageForFile(Filename);
+    renderFileCoverage(FileCoverage, FileReport);
+  }
+
+  emitDictKey("summary");
+  renderSummary(FileReport);
+
+  // End File.
+  emitDictEnd();
+}
+
+
+void CoverageExporterJson::renderFileCoverage(
+    const coverage::CoverageData &FileCoverage,
+    const FileCoverageSummary &FileReport) {
 
-    // Start List of Segments.
-    emitArrayStart();
 
-    for (const auto &Segment : FileCoverage)
-      renderSegment(Segment);
 
-    // End List of Segments.
-    emitArrayEnd();
 
-    emitDictKey("expansions");
 
-    // Start List of Expansions.
-    emitArrayStart();
 
-    for (const auto &Expansion : FileCoverage.getExpansions())
-      renderExpansion(Expansion);
 
-    // End List of Expansions.
-    emitArrayEnd();
-  }
 
-  emitDictKey("summary");
-  renderSummary(FileReport);
-
-  // End File.
-  emitDictEnd();
-}
-
 void CoverageExporterJson::renderSegment(
     const coverage::CoverageSegment &Segment) {
   // Start Segment.
   emitArrayStart();
 
   emitArrayElement(Segment.Line);
   emitArrayElement(Segment.Col);
   emitArrayElement(Segment.Count);