[MC] ELFObjectWriter: Removing unneeded variable and cast. NFC.

[sbc100]

Summary

getBeginSymbol is declared on the base class so we don't need ELFSec.

shouldRelocateWithSymbol is only called with instances of MCSymbolELF.

[sbc100]

• rebas

lib/MC/ELFObjectWriter.cpp

void writeSymbol(SymbolTableWriter &Writer, uint32_t StringIndex,
                    ELFSymbolData &MSD, const MCAsmLayout &Layout);
 
   // Start and end offset of each section
   using SectionOffsetsTy =
       std::map<const MCSectionELF *, std::pair<uint64_t, uint64_t>>;
 
   bool shouldRelocateWithSymbol(const MCAssembler &Asm,
                                 const MCSymbolRefExpr *RefA,
-                                const MCSymbol *Sym, uint64_t C,
+                                const MCSymbolELF *Sym, uint64_t C,
                                 unsigned Type) const;
 
   void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
                         const MCFragment *Fragment, const MCFixup &Fixup,
                         MCValue Target, uint64_t &FixedValue) override;
 
   // Map from a signature symbol to the group section index
   using RevGroupMapTy = DenseMap<const MCSymbol *, unsigned>;
Writer.writeSymbol(StringIndex, Info, Value, Size, Other, MSD.SectionIndex,
                      IsReserved);
 }
 
 // It is always valid to create a relocation with a symbol. It is preferable
 // to use a relocation with a section if that is possible. Using the section
 // allows us to omit some local symbols from the symbol table.
 bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
                                                const MCSymbolRefExpr *RefA,
-                                               const MCSymbol *S, uint64_t C,
+                                               const MCSymbolELF *Sym,
+                                               uint64_t C,
                                                unsigned Type) const {
-  const auto *Sym = cast_or_null<MCSymbolELF>(S);
   // A PCRel relocation to an absolute value has no symbol (or section). We
   // represent that with a relocation to a null section.
   if (!RefA)
     return false;
 
   MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
   switch (Kind) {
   default:
if (hasRelocationAddend()) {
     C = 0;
   }
 
   FixedValue = C;
 
   if (!RelocateWithSymbol) {
     const MCSection *SecA =
         (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
-    auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
     const auto *SectionSymbol =
-        ELFSec ? cast<MCSymbolELF>(ELFSec->getBeginSymbol()) : nullptr;
+        SecA ? cast<MCSymbolELF>(SecA->getBeginSymbol()) : nullptr;
     if (SectionSymbol)
       SectionSymbol->setUsedInReloc();
     ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend, SymA,
                            OriginalC);
     Relocations[&FixupSection].push_back(Rec);
     return;
   }