[DWARF] Add API to get data from MCDwarfLineStr

[ayermolo]

Summary

This API will be used in D121876, to get finalized string data for
.debug_line_str.

[ayermolo]

@dblaikie Do you think this is in your wheelhouse to review, or should I find someone else?
thanks

[dblaikie]

Generally we'd rather not commit untested functionality - /probably/ this should be either unit tested in this commit, or rolled into whatever commit calls/exercises the functionality. But if you reckon this is really the better separation, I won't insist on that, but give it some thought.

[ayermolo]

In D124052#3463847, @dblaikie wrote:

Generally we'd rather not commit untested functionality - /probably/ this should be either unit tested in this commit, or rolled into whatever commit calls/exercises the functionality. But if you reckon this is really the better separation, I won't insist on that, but give it some thought.

Thanks. I'll add a unit test. Probably more inline with what I have seen from other diffs of breaking them up if possible. The other commit is already pretty big.

[ayermolo]

modified one of the tests to test new API.

[ayermolo]

removing include that snuck in

[rafauler]

LGTM

llvm/include/llvm/MC/MCDwarf.h

public:
   /// v5 line table).
   explicit MCDwarfLineStr(MCContext &Ctx);
 
   /// Emit a reference to the string.
   void emitRef(MCStreamer *MCOS, StringRef Path);
 
   /// Emit the .debug_line_str section if appropriate.
   void emitSection(MCStreamer *MCOS);
+
+  /// Returns finalized section.
+  SmallString<0> getFinalizedData();
 };
 
 /// Instances of this class represent the name of the dwarf .file directive and
 /// its associated dwarf file number in the MC file. MCDwarfFile's are created
 /// and uniqued by the MCContext class. In Dwarf 4 file numbers start from 1;
 /// i.e. the entry with file number 1 is the first element in the vector of
 /// DwarfFiles and there is no MCDwarfFile with file number 0. In Dwarf 5 file
 /// numbers start from 0, with the MCDwarfFile with file number 0 being the

llvm/include/llvm/MC/StringTableBuilder.h

public:
   }
 
   size_t getSize() const { return Size; }
   void clear();
 
   void write(raw_ostream &OS) const;
   void write(uint8_t *Buf) const;
 
-private:
   bool isFinalized() const { return Finalized; }
 };
 
 } // end namespace llvm
 
 #endif // LLVM_MC_STRINGTABLEBUILDER_H

llvm/lib/MC/MCDwarf.cpp

static void emitAbsValue(MCStreamer &OS, const MCExpr *Value, unsigned Size) {
   const MCExpr *ABS = forceExpAbs(OS, Value);
   OS.emitValue(ABS, Size);
 }
 
 void MCDwarfLineStr::emitSection(MCStreamer *MCOS) {
   // Switch to the .debug_line_str section.
   MCOS->SwitchSection(
       MCOS->getContext().getObjectFileInfo()->getDwarfLineStrSection());
+  SmallString<0> Data = getFinalizedData();
+  MCOS->emitBinaryData(Data.str());
+}
+
+SmallString<0> MCDwarfLineStr::getFinalizedData() {
   // Emit the strings without perturbing the offsets we used.
+  if (!LineStrings.isFinalized())
     LineStrings.finalizeInOrder();
   SmallString<0> Data;
   Data.resize(LineStrings.getSize());
   LineStrings.write((uint8_t *)Data.data());
-  MCOS->emitBinaryData(Data.str());
+  return Data;
 }
 
 void MCDwarfLineStr::emitRef(MCStreamer *MCOS, StringRef Path) {
   int RefSize =
       dwarf::getDwarfOffsetByteSize(MCOS->getContext().getDwarfFormat());
   size_t Offset = LineStrings.add(Path);
   if (UseRelocs) {
     MCContext &Ctx = MCOS->getContext();