[CodeView] Use assembler directives for line tables

Adds a new family of .cv_* directives to LLVM's variant of GAS syntax:

- .cv_file: Similar to DWARF .file directives

- .cv_loc: Similar to the DWARF .loc directive, but starts with a
  function id. CodeView line tables are emitted by function instead of
  by compilation unit, so we needed an extra field to communicate this.
  Rather than overloading the .loc direction further, we decided it was
  better to have our own directive.

- .cv_stringtable: Emits the codeview string table at the current
  position. Currently this just contains the filenames as
  null-terminated strings.

- .cv_filechecksums: Emits the file checksum table for all files used
  with .cv_file so far. There is currently no support for emitting
  actual checksums, just filenames.

This moves the line table emission code down into the assembler.  This
is in preparation for implementing the inlined call site line table
format. The inline line table format encoding algorithm requires knowing
the absolute code offsets, so it must run after the assembler has laid
out the code.

David Majnemer collaborated on this patch.

llvm-svn: 259117

2 files changed, 60 insertions, 194 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
index f1716361a1d..b503f1dc31e 100644
--- a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
@@ -13,6 +13,7 @@
 
 #include "CodeViewDebug.h"
 #include "llvm/DebugInfo/CodeView/CodeView.h"
+#include "llvm/DebugInfo/CodeView/Line.h"
 #include "llvm/DebugInfo/CodeView/SymbolRecord.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCSymbol.h"
@@ -74,6 +75,18 @@ StringRef CodeViewDebug::getFullFilepath(const DIFile *File) {
   return Filepath;
 }
 
+unsigned CodeViewDebug::maybeRecordFile(const DIFile *F) {
+  unsigned NextId = FileIdMap.size() + 1;
+  auto Insertion = FileIdMap.insert(std::make_pair(F, NextId));
+  if (Insertion.second) {
+    // We have to compute the full filepath and emit a .cv_file directive.
+    StringRef FullPath = getFullFilepath(F);
+    NextId = Asm->OutStreamer->EmitCVFileDirective(NextId, FullPath);
+    assert(NextId == FileIdMap.size() && ".cv_file directive failed");
+  }
+  return Insertion.first->second;
+}
+
 void CodeViewDebug::maybeRecordLocation(DebugLoc DL,
                                         const MachineFunction *MF) {
   // Skip this instruction if it has the same location as the previous one.
@@ -85,15 +98,26 @@ void CodeViewDebug::maybeRecordLocation(DebugLoc DL,
     return;
 
   // Skip this line if it is longer than the maximum we can record.
-  if (DL.getLine() > COFF::CVL_MaxLineNumber)
+  LineInfo LI(DL.getLine(), DL.getLine(), /*IsStatement=*/true);
+  if (LI.getStartLine() != DL.getLine() || LI.isAlwaysStepInto() ||
+      LI.isNeverStepInto())
     return;
 
-  CurFn->LastLoc = DL;
+  ColumnInfo CI(DL.getCol(), /*EndColumn=*/0);
+  if (CI.getStartColumn() != DL.getCol())
+    return;
 
-  MCSymbol *MCL = Asm->MMI->getContext().createTempSymbol();
-  Asm->OutStreamer->EmitLabel(MCL);
-  CurFn->Instrs.push_back(MCL);
-  LabelsAndLocs[MCL] = DL;
+  if (!CurFn->HaveLineInfo)
+    CurFn->HaveLineInfo = true;
+  unsigned FileId = 0;
+  if (CurFn->LastLoc.get() && CurFn->LastLoc->getFile() == DL->getFile())
+    FileId = CurFn->LastFileId;
+  else
+    FileId = CurFn->LastFileId = maybeRecordFile(DL->getFile());
+  CurFn->LastLoc = DL;
+  Asm->OutStreamer->EmitCVLocDirective(CurFn->FuncId, FileId, DL.getLine(),
+                                       DL.getCol(), /*PrologueEnd=*/false,
+                                       /*IsStmt=*/false, DL->getFilename());
 }
 
 CodeViewDebug::CodeViewDebug(AsmPrinter *AP)
@@ -128,39 +152,17 @@ void CodeViewDebug::endModule() {
   // of the payload followed by the payload itself.  The subsections are 4-byte
   // aligned.
 
-  // Emit per-function debug information.  This code is extracted into a
-  // separate function for readability.
-  for (size_t I = 0, E = VisitedFunctions.size(); I != E; ++I)
-    emitDebugInfoForFunction(VisitedFunctions[I]);
+  // Emit per-function debug information.
+  for (auto &P : FnDebugInfo)
+    emitDebugInfoForFunction(P.first, P.second);
 
   // This subsection holds a file index to offset in string table table.
   Asm->OutStreamer->AddComment("File index to string table offset subsection");
-  Asm->EmitInt32(unsigned(ModuleSubstreamKind::FileChecksums));
-  size_t NumFilenames = FileNameRegistry.Infos.size();
-  Asm->EmitInt32(8 * NumFilenames);
-  for (size_t I = 0, E = FileNameRegistry.Filenames.size(); I != E; ++I) {
-    StringRef Filename = FileNameRegistry.Filenames[I];
-    // For each unique filename, just write its offset in the string table.
-    Asm->EmitInt32(FileNameRegistry.Infos[Filename].StartOffset);
-    // The function name offset is not followed by any additional data.
-    Asm->EmitInt32(0);
-  }
+  Asm->OutStreamer->EmitCVFileChecksumsDirective();
 
   // This subsection holds the string table.
   Asm->OutStreamer->AddComment("String table");
-  Asm->EmitInt32(unsigned(ModuleSubstreamKind::StringTable));
-  Asm->EmitInt32(FileNameRegistry.LastOffset);
-  // The payload starts with a null character.
-  Asm->EmitInt8(0);
-
-  for (size_t I = 0, E = FileNameRegistry.Filenames.size(); I != E; ++I) {
-    // Just emit unique filenames one by one, separated by a null character.
-    Asm->OutStreamer->EmitBytes(FileNameRegistry.Filenames[I]);
-    Asm->EmitInt8(0);
-  }
-
-  // No more subsections. Fill with zeros to align the end of the section by 4.
-  Asm->OutStreamer->EmitFill((-FileNameRegistry.LastOffset) % 4, 0);
+  Asm->OutStreamer->EmitCVStringTableDirective();
 
   clear();
 }
@@ -177,21 +179,13 @@ static void EmitLabelDiff(MCStreamer &Streamer,
   Streamer.EmitValue(AddrDelta, Size);
 }
 
-static const DIFile *getFileFromLoc(DebugLoc DL) {
-  return DL.get()->getScope()->getFile();
-}
-
-void CodeViewDebug::emitDebugInfoForFunction(const Function *GV) {
+void CodeViewDebug::emitDebugInfoForFunction(const Function *GV,
+                                             FunctionInfo &FI) {
   // For each function there is a separate subsection
   // which holds the PC to file:line table.
   const MCSymbol *Fn = Asm->getSymbol(GV);
   assert(Fn);
 
-  const FunctionInfo &FI = FnDebugInfo[GV];
-  if (FI.Instrs.empty())
-    return;
-  assert(FI.End && "Don't know where the function ends?");
-
   StringRef FuncName;
   if (auto *SP = getDISubprogram(GV))
     FuncName = SP->getDisplayName();
@@ -238,102 +232,8 @@ void CodeViewDebug::emitDebugInfoForFunction(const Function *GV) {
   // Every subsection must be aligned to a 4-byte boundary.
   Asm->OutStreamer->EmitFill((-FuncName.size()) % 4, 0);
 
-  // PCs/Instructions are grouped into segments sharing the same filename.
-  // Pre-calculate the lengths (in instructions) of these segments and store
-  // them in a map for convenience.  Each index in the map is the sequential
-  // number of the respective instruction that starts a new segment.
-  DenseMap<size_t, size_t> FilenameSegmentLengths;
-  size_t LastSegmentEnd = 0;
-  const DIFile *PrevFile = getFileFromLoc(LabelsAndLocs[FI.Instrs[0]]);
-  for (size_t J = 1, F = FI.Instrs.size(); J != F; ++J) {
-    const DIFile *CurFile = getFileFromLoc(LabelsAndLocs[FI.Instrs[J]]);
-    if (PrevFile == CurFile)
-      continue;
-    FilenameSegmentLengths[LastSegmentEnd] = J - LastSegmentEnd;
-    LastSegmentEnd = J;
-    PrevFile = CurFile;
-  }
-  FilenameSegmentLengths[LastSegmentEnd] = FI.Instrs.size() - LastSegmentEnd;
-
-  // Emit a line table subsection, required to do PC-to-file:line lookup.
-  Asm->OutStreamer->AddComment("Line table subsection for " + Twine(FuncName));
-  Asm->EmitInt32(unsigned(ModuleSubstreamKind::Lines));
-  MCSymbol *LineTableBegin = Asm->MMI->getContext().createTempSymbol(),
-           *LineTableEnd = Asm->MMI->getContext().createTempSymbol();
-  EmitLabelDiff(*Asm->OutStreamer, LineTableBegin, LineTableEnd);
-  Asm->OutStreamer->EmitLabel(LineTableBegin);
-
-  // Identify the function this subsection is for.
-  Asm->OutStreamer->EmitCOFFSecRel32(Fn);
-  Asm->OutStreamer->EmitCOFFSectionIndex(Fn);
-  // Insert flags after a 16-bit section index.
-  Asm->EmitInt16(COFF::DEBUG_LINE_TABLES_HAVE_COLUMN_RECORDS);
-
-  // Length of the function's code, in bytes.
-  EmitLabelDiff(*Asm->OutStreamer, Fn, FI.End);
-
-  // PC-to-linenumber lookup table:
-  MCSymbol *FileSegmentEnd = nullptr;
-
-  // The start of the last segment:
-  size_t LastSegmentStart = 0;
-
-  auto FinishPreviousChunk = [&] {
-    if (!FileSegmentEnd)
-      return;
-    for (size_t ColSegI = LastSegmentStart,
-                ColSegEnd = ColSegI + FilenameSegmentLengths[LastSegmentStart];
-         ColSegI != ColSegEnd; ++ColSegI) {
-      unsigned ColumnNumber = LabelsAndLocs[FI.Instrs[ColSegI]].getCol();
-      // Truncate the column number if it is longer than the maximum we can
-      // record.
-      if (ColumnNumber > COFF::CVL_MaxColumnNumber)
-        ColumnNumber = 0;
-      Asm->EmitInt16(ColumnNumber); // Start column
-      Asm->EmitInt16(0);            // End column
-    }
-    Asm->OutStreamer->EmitLabel(FileSegmentEnd);
-  };
-
-  for (size_t J = 0, F = FI.Instrs.size(); J != F; ++J) {
-    MCSymbol *Instr = FI.Instrs[J];
-    assert(LabelsAndLocs.count(Instr));
-
-    if (FilenameSegmentLengths.count(J)) {
-      // We came to a beginning of a new filename segment.
-      FinishPreviousChunk();
-      const DIFile *File = getFileFromLoc(LabelsAndLocs[FI.Instrs[J]]);
-      StringRef CurFilename = getFullFilepath(File);
-      size_t IndexInFileTable = FileNameRegistry.add(CurFilename);
-      // Each segment starts with the offset of the filename
-      // in the string table.
-      Asm->OutStreamer->AddComment(
-          "Segment for file '" + Twine(CurFilename) + "' begins");
-      MCSymbol *FileSegmentBegin = Asm->MMI->getContext().createTempSymbol();
-      Asm->OutStreamer->EmitLabel(FileSegmentBegin);
-      Asm->EmitInt32(8 * IndexInFileTable);
-
-      // Number of PC records in the lookup table.
-      size_t SegmentLength = FilenameSegmentLengths[J];
-      Asm->EmitInt32(SegmentLength);
-
-      // Full size of the segment for this filename, including the prev two
-      // records.
-      FileSegmentEnd = Asm->MMI->getContext().createTempSymbol();
-      EmitLabelDiff(*Asm->OutStreamer, FileSegmentBegin, FileSegmentEnd);
-      LastSegmentStart = J;
-    }
-
-    // The first PC with the given linenumber and the linenumber itself.
-    EmitLabelDiff(*Asm->OutStreamer, Fn, Instr);
-    uint32_t LineNumber = LabelsAndLocs[Instr].getLine();
-    assert(LineNumber <= COFF::CVL_MaxLineNumber);
-    uint32_t LineData = LineNumber | COFF::CVL_IsStatement;
-    Asm->EmitInt32(LineData);
-  }
-
-  FinishPreviousChunk();
-  Asm->OutStreamer->EmitLabel(LineTableEnd);
+  // We have an assembler directive that takes care of the whole line table.
+  Asm->OutStreamer->EmitCVLinetableDirective(FI.FuncId, Fn, FI.End);
 }
 
 void CodeViewDebug::beginFunction(const MachineFunction *MF) {
@@ -344,8 +244,8 @@ void CodeViewDebug::beginFunction(const MachineFunction *MF) {
 
   const Function *GV = MF->getFunction();
   assert(FnDebugInfo.count(GV) == false);
-  VisitedFunctions.push_back(GV);
   CurFn = &FnDebugInfo[GV];
+  CurFn->FuncId = NextFuncId++;
 
   // Find the end of the function prolog.
   // FIXME: is there a simpler a way to do this? Can we just search
@@ -384,9 +284,9 @@ void CodeViewDebug::endFunction(const MachineFunction *MF) {
   assert(FnDebugInfo.count(GV));
   assert(CurFn == &FnDebugInfo[GV]);
 
-  if (CurFn->Instrs.empty()) {
+  // Don't emit anything if we don't have any line tables.
+  if (!CurFn->HaveLineInfo) {
     FnDebugInfo.erase(GV);
-    VisitedFunctions.pop_back();
   } else {
     CurFn->End = Asm->getFunctionEnd();
   }
diff --git a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h
index 4294b4fd694..77b5ed39c1f 100644
--- a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h
+++ b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h
@@ -37,72 +37,38 @@ class LLVM_LIBRARY_VISIBILITY CodeViewDebug : public AsmPrinterHandler {
   // to the end of the function.
   struct FunctionInfo {
     DebugLoc LastLoc;
-    SmallVector<MCSymbol *, 10> Instrs;
-    MCSymbol *End;
-    FunctionInfo() : End(nullptr) {}
+    MCSymbol *End = nullptr;
+    unsigned FuncId = 0;
+    unsigned LastFileId;
+    bool HaveLineInfo = false;
   };
   FunctionInfo *CurFn;
 
-  typedef DenseMap<const Function *, FunctionInfo> FnDebugInfoTy;
-  FnDebugInfoTy FnDebugInfo;
-  // Store the functions we've visited in a vector so we can maintain a stable
-  // order while emitting subsections.
-  SmallVector<const Function *, 10> VisitedFunctions;
-
-  DenseMap<MCSymbol *, DebugLoc> LabelsAndLocs;
-
-  // FileNameRegistry - Manages filenames observed while generating debug info
-  // by filtering out duplicates and bookkeeping the offsets in the string
-  // table to be generated.
-  struct FileNameRegistryTy {
-    SmallVector<StringRef, 10> Filenames;
-    struct PerFileInfo {
-      size_t FilenameID, StartOffset;
-    };
-    StringMap<PerFileInfo> Infos;
-
-    // The offset in the string table where we'll write the next unique
-    // filename.
-    size_t LastOffset;
-
-    FileNameRegistryTy() {
-      clear();
-    }
-
-    // Add Filename to the registry, if it was not observed before.
-    size_t add(StringRef Filename) {
-      size_t OldSize = Infos.size();
-      bool Inserted;
-      StringMap<PerFileInfo>::iterator It;
-      std::tie(It, Inserted) = Infos.insert(
-          std::make_pair(Filename, PerFileInfo{OldSize, LastOffset}));
-      if (Inserted) {
-        LastOffset += Filename.size() + 1;
-        Filenames.push_back(Filename);
-      }
-      return It->second.FilenameID;
-    }
-
-    void clear() {
-      LastOffset = 1;
-      Infos.clear();
-      Filenames.clear();
-    }
-  } FileNameRegistry;
+  unsigned NextFuncId = 0;
+
+  /// Remember some debug info about each function. Keep it in a stable order to
+  /// emit at the end of the TU.
+  MapVector<const Function *, FunctionInfo> FnDebugInfo;
+
+  /// Map from DIFile to .cv_file id.
+  DenseMap<const DIFile *, unsigned> FileIdMap;
 
   typedef std::map<const DIFile *, std::string> FileToFilepathMapTy;
   FileToFilepathMapTy FileToFilepathMap;
   StringRef getFullFilepath(const DIFile *S);
 
+  unsigned maybeRecordFile(const DIFile *F);
+
   void maybeRecordLocation(DebugLoc DL, const MachineFunction *MF);
 
   void clear() {
     assert(CurFn == nullptr);
-    FileNameRegistry.clear();
-    LabelsAndLocs.clear();
+    FileIdMap.clear();
+    FnDebugInfo.clear();
+    FileToFilepathMap.clear();
   }
 
-  void emitDebugInfoForFunction(const Function *GV);
+  void emitDebugInfoForFunction(const Function *GV, FunctionInfo &FI);
 
 public:
   CodeViewDebug(AsmPrinter *Asm);