[DWARFYAML] Make the debug_addr section optional.

[Higuoxing]

Summary

This patch makes the debug_addr section optional. When an empty
debug_addr section is specified, yaml2obj only emits a section header
for it.

[jhenderson]

LGTM, with nit.

llvm/test/tools/yaml2obj/ELF/DWARF/debug-addr.yaml

639

I think you can drop --section-data from this line, right?

[Higuoxing]

Address review comment.

llvm/test/tools/yaml2obj/ELF/DWARF/debug-addr.yaml

639

Yes, thanks!

llvm/include/llvm/ObjectYAML/DWARFYAML.h

 struct Data {
   bool IsLittleEndian;
   bool Is64BitAddrSize;
   std::vector<AbbrevTable> DebugAbbrev;
   Optional<std::vector<StringRef>> DebugStrings;
   Optional<std::vector<StringOffsetsTable>> DebugStrOffsets;
   Optional<std::vector<ARange>> DebugAranges;
   std::vector<Ranges> DebugRanges;
-  std::vector<AddrTableEntry> DebugAddr;
+  Optional<std::vector<AddrTableEntry>> DebugAddr;
   Optional<PubSection> PubNames;
   Optional<PubSection> PubTypes;
 
   Optional<PubSection> GNUPubNames;
   Optional<PubSection> GNUPubTypes;
 
   std::vector<Unit> CompileUnits;
 

llvm/lib/ObjectYAML/DWARFEmitter.cpp

for (const DWARFYAML::LineTable &LineTable : DI.DebugLines) {
     writeDWARFOffset(HeaderLength, LineTable.Format, OS, DI.IsLittleEndian);
     OS.write(Buffer.data(), Buffer.size());
   }
 
   return Error::success();
 }
 
 Error DWARFYAML::emitDebugAddr(raw_ostream &OS, const Data &DI) {
-  for (const AddrTableEntry &TableEntry : DI.DebugAddr) {
+  for (const AddrTableEntry &TableEntry : *DI.DebugAddr) {
     uint8_t AddrSize;
     if (TableEntry.AddrSize)
       AddrSize = *TableEntry.AddrSize;
     else
       AddrSize = DI.Is64BitAddrSize ? 8 : 4;
 
     uint64_t Length;
     if (TableEntry.Length)

llvm/lib/ObjectYAML/DWARFYAML.cpp

SetVector<StringRef> DWARFYAML::Data::getNonEmptySectionNames() const {
   if (DebugStrings)
     SecNames.insert("debug_str");
   if (DebugAranges)
     SecNames.insert("debug_aranges");
   if (!DebugRanges.empty())
     SecNames.insert("debug_ranges");
   if (!DebugLines.empty())
     SecNames.insert("debug_line");
-  if (!DebugAddr.empty())
+  if (DebugAddr)
     SecNames.insert("debug_addr");
   if (!DebugAbbrev.empty())
     SecNames.insert("debug_abbrev");
   if (!CompileUnits.empty())
     SecNames.insert("debug_info");
   if (PubNames)
     SecNames.insert("debug_pubnames");
   if (PubTypes)

llvm/test/tools/yaml2obj/ELF/DWARF/debug-addr.yaml

FileHeader:
   Data:  ELFDATA2LSB
   Type:  ET_EXEC
 DWARF:
   debug_addr:
     - Version:      5
       [[SIZENAME]]: 3
       Entries:
         - Address: 0x1234
+
+## n) Test that the .debug_addr section header is emitted if the "debug_addr"
+## entry is empty.
+
+# RUN: yaml2obj --docnum=12 %s -o %t12.o
+# RUN: llvm-readobj --sections %t12.o | \
+# RUN:   FileCheck %s -DSIZE=0 -DADDRALIGN=1 --check-prefix=SHDR
+
+--- !ELF
+FileHeader:
+  Class: ELFCLASS64
+  Data:  ELFDATA2LSB
+  Type:  ET_EXEC
+DWARF:
+  debug_addr: []