[WebAssembly] MC: Refactor section creation code

[sbc100]

Summary

Remove the use of default argument in favor of a separate
startCustomSection method.

lib/MC/WasmObjectWriter.cpp

class WasmObjectWriter : public MCObjectWriter {
   unsigned NumGlobalImports = 0;
 
   // TargetObjectWriter wrappers.
   bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
   unsigned getRelocType(const MCValue &Target, const MCFixup &Fixup) const {
     return TargetObjectWriter->getRelocType(Target, Fixup);
   }
 
-  void startSection(SectionBookkeeping &Section, unsigned SectionId,
-                    const char *Name = nullptr);
+  void startSection(SectionBookkeeping &Section, unsigned SectionId);
+  void startCustomSection(SectionBookkeeping &Section, StringRef Name);
   void endSection(SectionBookkeeping &Section);
 
 public:
   WasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW,
                    raw_pwrite_stream &OS)
       : MCObjectWriter(OS, /*IsLittleEndian=*/true),
         TargetObjectWriter(std::move(MOTW)) {}
 

 };
 
 } // end anonymous namespace
 
 WasmObjectWriter::~WasmObjectWriter() {}
 
 // Write out a section header and a patchable section size field.
 void WasmObjectWriter::startSection(SectionBookkeeping &Section,
-                                    unsigned SectionId,
-                                    const char *Name) {
-  assert((Name != nullptr) == (SectionId == wasm::WASM_SEC_CUSTOM) &&
-         "Only custom sections can have names");
-
-  DEBUG(dbgs() << "startSection " << SectionId << ": " << Name << "\n");
+                                    unsigned SectionId) {
+  DEBUG(dbgs() << "startSection " << SectionId << "\n");
   write8(SectionId);
 
   Section.SizeOffset = getStream().tell();
 
   // The section size. We don't know the size yet, so reserve enough space
   // for any 32-bit value; we'll patch it later.
   encodeULEB128(UINT32_MAX, getStream());
 
   // The position where the section starts, for measuring its size.
   Section.ContentsOffset = getStream().tell();
+}
 
+void WasmObjectWriter::startCustomSection(SectionBookkeeping &Section,
+                                          StringRef Name) {
+  DEBUG(dbgs() << "startCustomSection " << Name << "\n");
+  startSection(Section, wasm::WASM_SEC_CUSTOM);
   // Custom sections in wasm also have a string identifier.
-  if (SectionId == wasm::WASM_SEC_CUSTOM) {
-    assert(Name);
-    writeString(Name);
-  }
-}
 
 // Now that the section is complete and we know how big it is, patch up the
 // section size field at the start of the section.
 void WasmObjectWriter::endSection(SectionBookkeeping &Section) {
   uint64_t Size = getStream().tell() - Section.ContentsOffset;
   if (uint32_t(Size) != Size)
     report_fatal_error("section size does not fit in a uint32_t");
 

 void WasmObjectWriter::writeCodeRelocSection() {
   // See: https://github.com/WebAssembly/tool-conventions/blob/master/Linking.md
   // for descriptions of the reloc sections.
 
   if (CodeRelocations.empty())
     return;
 
   SectionBookkeeping Section;
-  startSection(Section, wasm::WASM_SEC_CUSTOM, "reloc.CODE");
+  startCustomSection(Section, "reloc.CODE");
 
   encodeULEB128(wasm::WASM_SEC_CODE, getStream());
   encodeULEB128(CodeRelocations.size(), getStream());
 
   writeRelocations(CodeRelocations);
 
   endSection(Section);
 }
 
 void WasmObjectWriter::writeDataRelocSection() {
   // See: https://github.com/WebAssembly/tool-conventions/blob/master/Linking.md
   // for descriptions of the reloc sections.
 
   if (DataRelocations.empty())
     return;
 
   SectionBookkeeping Section;
-  startSection(Section, wasm::WASM_SEC_CUSTOM, "reloc.DATA");
+  startCustomSection(Section, "reloc.DATA");
 
   encodeULEB128(wasm::WASM_SEC_DATA, getStream());
   encodeULEB128(DataRelocations.size(), getStream());
 
   writeRelocations(DataRelocations);
 
   endSection(Section);
 }
 
 void WasmObjectWriter::writeLinkingMetaDataSection(
     ArrayRef<wasm::WasmSymbolInfo> SymbolInfos,
     ArrayRef<std::pair<uint16_t, uint32_t>> InitFuncs,
     const std::map<StringRef, std::vector<WasmComdatEntry>> &Comdats) {
   SectionBookkeeping Section;
-  startSection(Section, wasm::WASM_SEC_CUSTOM, "linking");
+  startCustomSection(Section, "linking");
   SectionBookkeeping SubSection;
 
   if (SymbolInfos.size() != 0) {
     startSection(SubSection, wasm::WASM_SYMBOL_TABLE);
     encodeULEB128(SymbolInfos.size(), getStream());
     for (const wasm::WasmSymbolInfo &Sym : SymbolInfos) {
       encodeULEB128(Sym.Kind, getStream());
       encodeULEB128(Sym.Flags, getStream());
void WasmObjectWriter::writeLinkingMetaDataSection(
 
   endSection(Section);
 }
 
 void WasmObjectWriter::writeUserCustomSections(
     ArrayRef<WasmCustomSection> CustomSections) {
   for (const auto &CustomSection : CustomSections) {
     SectionBookkeeping Section;
-    startSection(Section, wasm::WASM_SEC_CUSTOM,
-                 CustomSection.Name.str().c_str());
+    startCustomSection(Section, CustomSection.Name);
     writeBytes(CustomSection.Contents);
     endSection(Section);
   }
 }
 
 uint32_t WasmObjectWriter::getFunctionType(const MCSymbolWasm& Symbol) {
   assert(Symbol.isFunction());
   assert(TypeIndices.count(&Symbol));