[DWARF][NFC] Refactor a function to return Optional<> instead of bool

[wolfgangp]

Summary

Minor refactor of DWARFUnit::getStringOffsetSectionItem(). Fairly self-explanatory.

[dblaikie]

Looks good - thanks!

llvm/trunk/include/llvm/DebugInfo/DWARF/DWARFUnit.h

public:
   void updateAddressDieMap(DWARFDie Die);
 
   void setRangesSection(const DWARFSection *RS, uint32_t Base) {
     RangeSection = RS;
     RangeSectionBase = Base;
   }
 
   Optional<SectionedAddress> getAddrOffsetSectionItem(uint32_t Index) const;
-  bool getStringOffsetSectionItem(uint32_t Index, uint64_t &Result) const;
+  Optional<uint64_t> getStringOffsetSectionItem(uint32_t Index) const;
 
   DWARFDataExtractor getDebugInfoExtractor() const;
 
   DataExtractor getStringExtractor() const {
     return DataExtractor(StringSection, false, 0);
   }
 
   /// Extract the range list referenced by this compile unit from the

llvm/trunk/lib/DebugInfo/DWARF/DWARFFormValue.cpp

if (Form == DW_FORM_line_strp) {
     // .debug_line_str is tracked in the Context.
     if (const char *Str = C->getLineStringExtractor().getCStr(&Offset))
       return Str;
     return None;
   }
   if (Form == DW_FORM_GNU_str_index || Form == DW_FORM_strx ||
       Form == DW_FORM_strx1 || Form == DW_FORM_strx2 || Form == DW_FORM_strx3 ||
       Form == DW_FORM_strx4) {
-    uint64_t StrOffset;
-    if (!U || !U->getStringOffsetSectionItem(Offset, StrOffset))
+    if (!U)
+      return None;
+    Optional<uint64_t> StrOffset = U->getStringOffsetSectionItem(Offset);
+    if (!StrOffset)
       return None;
-    Offset = StrOffset;
+    Offset = *StrOffset;
   }
   // Prefer the Unit's string extractor, because for .dwo it will point to
   // .debug_str.dwo, while the Context's extractor always uses .debug_str.
   if (U) {
     if (const char *Str = U->getStringExtractor().getCStr(&Offset))
       return Str;
     return None;
   }

llvm/trunk/lib/DebugInfo/DWARF/DWARFUnit.cpp

if (AddrOffsetSection->Data.size() < Offset + getAddressByteSize())
     return None;
   DWARFDataExtractor DA(Context.getDWARFObj(), *AddrOffsetSection,
                         isLittleEndian, getAddressByteSize());
   uint64_t Section;
   uint64_t Address = DA.getRelocatedAddress(&Offset, &Section);
   return {{Address, Section}};
 }
 
-bool DWARFUnit::getStringOffsetSectionItem(uint32_t Index,
-                                           uint64_t &Result) const {
+Optional<uint64_t> DWARFUnit::getStringOffsetSectionItem(uint32_t Index) const {
   if (!StringOffsetsTableContribution)
-    return false;
+    return None;
   unsigned ItemSize = getDwarfStringOffsetsByteSize();
   uint32_t Offset = getStringOffsetsBase() + Index * ItemSize;
   if (StringOffsetSection.Data.size() < Offset + ItemSize)
-    return false;
+    return None;
   DWARFDataExtractor DA(Context.getDWARFObj(), StringOffsetSection,
                         isLittleEndian, 0);
-  Result = DA.getRelocatedValue(ItemSize, &Offset);
-  return true;
+  return DA.getRelocatedValue(ItemSize, &Offset);
 }
 
 bool DWARFUnitHeader::extract(DWARFContext &Context,
                               const DWARFDataExtractor &debug_info,
                               uint32_t *offset_ptr,
                               DWARFSectionKind SectionKind,
                               const DWARFUnitIndex *Index) {
   Offset = *offset_ptr;