[DebugInfo] Move function from line table to the prologue (NFC)

[JDevlieghere]

Summary

In LLDB, when parsing type units, we don't need to parse the whole line table. Instead, we only need to parse the support files from the line table prologue. To make that possible, this patch moves the respective functions from the LineTable into the Prologue. Because I don't think users of the LineTable should have to know that these files come from the Prologue, I've left the original methods in place, and made them redirect to the LineTable.

[phosek]

This change broke lld:

/b/s/w/ir/k/llvm-project/lld/ELF/InputFiles.cpp:323:28: error: conversion function from 'nullptr_t' to 'llvm::StringRef' invokes a deleted function
          it->second.file, nullptr,
                           ^~~~~~~
/b/s/w/ir/k/llvm-project/lld/ELF/InputFiles.cpp:1637:21: note: in instantiation of member function 'lld::elf::ObjFile<llvm::object::ELFType<llvm::support::little, false> >::getVariableLoc' requested here
template class elf::ObjFile<ELF32LE>;
                    ^
/b/s/w/ir/k/llvm-project/llvm/include/llvm/ADT/StringRef.h:79:5: note: 'StringRef' has been explicitly marked deleted here
    StringRef(std::nullptr_t) = delete;
    ^
/b/s/w/ir/k/llvm-project/llvm/include/llvm/DebugInfo/DWARF/DWARFDebugLine.h:263:59: note: passing argument to parameter 'CompDir' here
    bool getFileNameByIndex(uint64_t FileIndex, StringRef CompDir,
                                                          ^
/b/s/w/ir/k/llvm-project/lld/ELF/InputFiles.cpp:323:28: error: conversion function from 'nullptr_t' to 'llvm::StringRef' invokes a deleted function
          it->second.file, nullptr,
                           ^~~~~~~
/b/s/w/ir/k/llvm-project/lld/ELF/InputFiles.cpp:1638:21: note: in instantiation of member function 'lld::elf::ObjFile<llvm::object::ELFType<llvm::support::big, false> >::getVariableLoc' requested here
template class elf::ObjFile<ELF32BE>;
                    ^
/b/s/w/ir/k/llvm-project/llvm/include/llvm/ADT/StringRef.h:79:5: note: 'StringRef' has been explicitly marked deleted here
    StringRef(std::nullptr_t) = delete;
    ^
/b/s/w/ir/k/llvm-project/llvm/include/llvm/DebugInfo/DWARF/DWARFDebugLine.h:263:59: note: passing argument to parameter 'CompDir' here
    bool getFileNameByIndex(uint64_t FileIndex, StringRef CompDir,
                                                          ^
/b/s/w/ir/k/llvm-project/lld/ELF/InputFiles.cpp:323:28: error: conversion function from 'nullptr_t' to 'llvm::StringRef' invokes a deleted function
          it->second.file, nullptr,
                           ^~~~~~~
/b/s/w/ir/k/llvm-project/lld/ELF/InputFiles.cpp:1639:21: note: in instantiation of member function 'lld::elf::ObjFile<llvm::object::ELFType<llvm::support::little, true> >::getVariableLoc' requested here
template class elf::ObjFile<ELF64LE>;
                    ^
/b/s/w/ir/k/llvm-project/llvm/include/llvm/ADT/StringRef.h:79:5: note: 'StringRef' has been explicitly marked deleted here
    StringRef(std::nullptr_t) = delete;
    ^
/b/s/w/ir/k/llvm-project/llvm/include/llvm/DebugInfo/DWARF/DWARFDebugLine.h:263:59: note: passing argument to parameter 'CompDir' here
    bool getFileNameByIndex(uint64_t FileIndex, StringRef CompDir,
                                                          ^
/b/s/w/ir/k/llvm-project/lld/ELF/InputFiles.cpp:323:28: error: conversion function from 'nullptr_t' to 'llvm::StringRef' invokes a deleted function
          it->second.file, nullptr,
                           ^~~~~~~
/b/s/w/ir/k/llvm-project/lld/ELF/InputFiles.cpp:1640:21: note: in instantiation of member function 'lld::elf::ObjFile<llvm::object::ELFType<llvm::support::big, true> >::getVariableLoc' requested here
template class elf::ObjFile<ELF64BE>;
                    ^
/b/s/w/ir/k/llvm-project/llvm/include/llvm/ADT/StringRef.h:79:5: note: 'StringRef' has been explicitly marked deleted here
    StringRef(std::nullptr_t) = delete;
    ^
/b/s/w/ir/k/llvm-project/llvm/include/llvm/DebugInfo/DWARF/DWARFDebugLine.h:263:59: note: passing argument to parameter 'CompDir' here
    bool getFileNameByIndex(uint64_t FileIndex, StringRef CompDir,
                                                          ^
4 errors generated.

llvm/include/llvm/DebugInfo/DWARF/DWARFDebugLine.h

struct Prologue {
     uint32_t getStatementTableLength() const {
       return TotalLength + sizeofTotalLength() - getLength();
     }
 
     int32_t getMaxLineIncrementForSpecialOpcode() const {
       return LineBase + (int8_t)LineRange - 1;
     }
 
+    /// Get DWARF-version aware access to the file name entry at the provided
+    /// index.
+    const llvm::DWARFDebugLine::FileNameEntry &
+    getFileNameEntry(uint64_t Index) const;
+
+    bool hasFileAtIndex(uint64_t FileIndex) const;
+
+    bool getFileNameByIndex(uint64_t FileIndex, StringRef CompDir,
+                            DILineInfoSpecifier::FileLineInfoKind Kind,
+                            std::string &Result) const;
+
     void clear();
     void dump(raw_ostream &OS, DIDumpOptions DumpOptions) const;
     Error parse(const DWARFDataExtractor &DebugLineData, uint32_t *OffsetPtr,
                 const DWARFContext &Ctx, const DWARFUnit *U = nullptr);
   };
 
   /// Standard .debug_line state machine structure.
   struct Row {
struct LineTable {
 
     /// Returns the index of the row with file/line info for a given address,
     /// or UnknownRowIndex if there is no such row.
     uint32_t lookupAddress(object::SectionedAddress Address) const;
 
     bool lookupAddressRange(object::SectionedAddress Address, uint64_t Size,
                             std::vector<uint32_t> &Result) const;
 
-    bool hasFileAtIndex(uint64_t FileIndex) const;
+    bool hasFileAtIndex(uint64_t FileIndex) const {
+      return Prologue.hasFileAtIndex(FileIndex);
+    }
 
     /// Extracts filename by its index in filename table in prologue.
     /// In Dwarf 4, the files are 1-indexed and the current compilation file
     /// name is not represented in the list. In DWARF v5, the files are
     /// 0-indexed and the primary source file has the index 0.
     /// Returns true on success.
-    bool getFileNameByIndex(uint64_t FileIndex, const char *CompDir,
+    bool getFileNameByIndex(uint64_t FileIndex, StringRef CompDir,
                             DILineInfoSpecifier::FileLineInfoKind Kind,
-                            std::string &Result) const;
+                            std::string &Result) const {
+      return Prologue.getFileNameByIndex(FileIndex, CompDir, Kind, Result);
+    }
 
     /// Fills the Result argument with the file and line information
     /// corresponding to Address. Returns true on success.
     bool getFileLineInfoForAddress(object::SectionedAddress Address,
                                    const char *CompDir,
                                    DILineInfoSpecifier::FileLineInfoKind Kind,
                                    DILineInfo &Result) const;
 
     void dump(raw_ostream &OS, DIDumpOptions DumpOptions) const;
     void clear();
 
     /// Parse prologue and all rows.
     Error parse(
         DWARFDataExtractor &DebugLineData, uint32_t *OffsetPtr,
         const DWARFContext &Ctx, const DWARFUnit *U,
         std::function<void(Error)> RecoverableErrorCallback,
         raw_ostream *OS = nullptr);
 
-    /// Get DWARF-version aware access to the file name entry at the provided
-    /// index.
-    const llvm::DWARFDebugLine::FileNameEntry &
-        getFileNameEntry(uint64_t Index) const;
-
     using RowVector = std::vector<Row>;
     using RowIter = RowVector::const_iterator;
     using SequenceVector = std::vector<Sequence>;
     using SequenceIter = SequenceVector::const_iterator;
 
     struct Prologue Prologue;
     RowVector Rows;
     SequenceVector Sequences;

llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp

default:
     // We only care about values we consider optional, and new values may be
     // added in the vendor extension range, so we do not match exhaustively.
     break;
   }
 }
 
 DWARFDebugLine::Prologue::Prologue() { clear(); }
 
+bool DWARFDebugLine::Prologue::hasFileAtIndex(uint64_t FileIndex) const {
+  uint16_t DwarfVersion = getVersion();
+  assert(DwarfVersion != 0 &&
+         "line table prologue has no dwarf version information");
+  if (DwarfVersion >= 5)
+    return FileIndex < FileNames.size();
+  return FileIndex != 0 && FileIndex <= FileNames.size();
+}
+
+const llvm::DWARFDebugLine::FileNameEntry &
+DWARFDebugLine::Prologue::getFileNameEntry(uint64_t Index) const {
+  uint16_t DwarfVersion = getVersion();
+  assert(DwarfVersion != 0 &&
+         "line table prologue has no dwarf version information");
+  // In DWARF v5 the file names are 0-indexed.
+  if (DwarfVersion >= 5)
+    return FileNames[Index];
+  return FileNames[Index - 1];
+}
+
 void DWARFDebugLine::Prologue::clear() {
   TotalLength = PrologueLength = 0;
   SegSelectorSize = 0;
   MinInstLength = MaxOpsPerInst = DefaultIsStmt = LineBase = LineRange = 0;
   OpcodeBase = 0;
   FormParams = dwarf::FormParams({0, 0, DWARF32});
   ContentTypes = ContentTypeTracker();
   StandardOpcodeLengths.clear();
while (SeqPos != LastSeq && SeqPos->LowPC < EndAddr) {
     }
 
     ++SeqPos;
   }
 
   return true;
 }
 
-bool DWARFDebugLine::LineTable::hasFileAtIndex(uint64_t FileIndex) const {
-  uint16_t DwarfVersion = Prologue.getVersion();
-  assert(DwarfVersion != 0 && "LineTable has no dwarf version information");
-  if (DwarfVersion >= 5)
-    return FileIndex < Prologue.FileNames.size();
-  return FileIndex != 0 && FileIndex <= Prologue.FileNames.size();
-}
-
-const llvm::DWARFDebugLine::FileNameEntry &
-DWARFDebugLine::LineTable::getFileNameEntry(uint64_t Index) const {
-  uint16_t DwarfVersion = Prologue.getVersion();
-  assert(DwarfVersion != 0 && "LineTable has no dwarf version information");
-  // In DWARF v5 the file names are 0-indexed.
-  if (DwarfVersion >= 5)
-    return Prologue.FileNames[Index];
-  else
-    return Prologue.FileNames[Index - 1];
-}
-
 Optional<StringRef> DWARFDebugLine::LineTable::getSourceByIndex(uint64_t FileIndex,
                                                                 FileLineInfoKind Kind) const {
-  if (Kind == FileLineInfoKind::None || !hasFileAtIndex(FileIndex))
+  if (Kind == FileLineInfoKind::None || !Prologue.hasFileAtIndex(FileIndex))
     return None;
-  const FileNameEntry &Entry = getFileNameEntry(FileIndex);
+  const FileNameEntry &Entry = Prologue.getFileNameEntry(FileIndex);
   if (Optional<const char *> source = Entry.Source.getAsCString())
     return StringRef(*source);
   return None;
 }
 
 static bool isPathAbsoluteOnWindowsOrPosix(const Twine &Path) {
   // Debug info can contain paths from any OS, not necessarily
   // an OS we're currently running on. Moreover different compilation units can
   // be compiled on different operating systems and linked together later.
   return sys::path::is_absolute(Path, sys::path::Style::posix) ||
          sys::path::is_absolute(Path, sys::path::Style::windows);
 }
 
-bool DWARFDebugLine::LineTable::getFileNameByIndex(uint64_t FileIndex,
-                                                   const char *CompDir,
-                                                   FileLineInfoKind Kind,
-                                                   std::string &Result) const {
+bool DWARFDebugLine::Prologue::getFileNameByIndex(uint64_t FileIndex,
+                                                  StringRef CompDir,
   if (Kind == FileLineInfoKind::None || !hasFileAtIndex(FileIndex))
     return false;
   const FileNameEntry &Entry = getFileNameEntry(FileIndex);
   StringRef FileName = Entry.Name.getAsCString().getValue();
   if (Kind != FileLineInfoKind::AbsoluteFilePath ||
       isPathAbsoluteOnWindowsOrPosix(FileName)) {
     Result = FileName;
     return true;
   }
 
   SmallString<16> FilePath;
   StringRef IncludeDir;
   // Be defensive about the contents of Entry.
-  if (Prologue.getVersion() >= 5) {
-    if (Entry.DirIdx < Prologue.IncludeDirectories.size())
-      IncludeDir =
-          Prologue.IncludeDirectories[Entry.DirIdx].getAsCString().getValue();
+  if (getVersion() >= 5) {
+    if (Entry.DirIdx < IncludeDirectories.size())
+      IncludeDir = IncludeDirectories[Entry.DirIdx].getAsCString().getValue();
   } else {
-    if (0 < Entry.DirIdx && Entry.DirIdx <= Prologue.IncludeDirectories.size())
-      IncludeDir = Prologue.IncludeDirectories[Entry.DirIdx - 1]
-                       .getAsCString()
-                       .getValue();
+    if (0 < Entry.DirIdx && Entry.DirIdx <= IncludeDirectories.size())
+      IncludeDir =
+          IncludeDirectories[Entry.DirIdx - 1].getAsCString().getValue();
 
     // We may still need to append compilation directory of compile unit.
     // We know that FileName is not absolute, the only way to have an
     // absolute path at this point would be if IncludeDir is absolute.
-    if (CompDir && !isPathAbsoluteOnWindowsOrPosix(IncludeDir))
+    if (!CompDir.empty() && !isPathAbsoluteOnWindowsOrPosix(IncludeDir))
       sys::path::append(FilePath, CompDir);
   }
 
   // sys::path::append skips empty strings.
   sys::path::append(FilePath, IncludeDir, FileName);
   Result = FilePath.str();
   return true;
 }