[ELF] - Move DependentSections vector from InputSection to InputSectionBase

[grimar]

Summary

I splitted it from D29273.
Since we plan to make relocatable sections as dependent for target ones for
--emit-relocs implementation, this change is required to support .eh_frame case.

EhInputSection inherets from InputSectionBase and not from InputSection.
So for case when it has relocation section, it should be able to access DependentSections
vector.

This case is real for Linux kernel.

lld/trunk/ELF/InputFiles.cpp

for (const Elf_Shdr &Sec : ObjSections) {
     }
 
     // .ARM.exidx sections have a reverse dependency on the InputSection they
     // have a SHF_LINK_ORDER dependency, this is identified by the sh_link.
     if (Sec.sh_flags & SHF_LINK_ORDER) {
       if (Sec.sh_link >= Sections.size())
         fatal(toString(this) + ": invalid sh_link index: " +
               Twine(Sec.sh_link));
-      auto *IS = cast<InputSection<ELFT>>(Sections[Sec.sh_link]);
-      IS->DependentSections.push_back(Sections[I]);
+      Sections[Sec.sh_link]->DependentSections.push_back(Sections[I]);
     }
   }
 }
 
 template <class ELFT>
 InputSectionBase<ELFT> *
 elf::ObjectFile<ELFT>::getRelocTarget(const Elf_Shdr &Sec) {
   uint32_t Idx = Sec.sh_info;

lld/trunk/ELF/InputSection.h

public:
 
   // This pointer points to the "real" instance of this instance.
   // Usually Repl == this. However, if ICF merges two sections,
   // Repl pointer of one section points to another section. So,
   // if you need to get a pointer to this instance, do not use
   // this but instead this->Repl.
   InputSectionBase<ELFT> *Repl;
 
+  // InputSections that are dependent on us (reverse dependency for GC)
+  llvm::TinyPtrVector<InputSectionBase<ELFT> *> DependentSections;
+
   // Returns the size of this section (even if this is a common or BSS.)
   size_t getSize() const;
 
   OutputSectionBase *getOutputSection() const;
 
   ObjectFile<ELFT> *getFile() const { return File; }
   llvm::object::ELFFile<ELFT> getObj() const { return File->getObj(); }
   uintX_t getOffset(const DefinedRegular<ELFT> &Sym) const;
public:
   // Write this section to a mmap'ed file, assuming Buf is pointing to
   // beginning of the output section.
   void writeTo(uint8_t *Buf);
 
   // The offset from beginning of the output sections this section was assigned
   // to. The writer sets a value.
   uint64_t OutSecOff = 0;
 
-  // InputSections that are dependent on us (reverse dependency for GC)
-  llvm::TinyPtrVector<InputSectionBase<ELFT> *> DependentSections;
-
   static bool classof(const InputSectionData *S);
 
   InputSectionBase<ELFT> *getRelocatedSection();
 
   template <class RelTy>
   void relocateNonAlloc(uint8_t *Buf, llvm::ArrayRef<RelTy> Rels);
 
   // Used by ICF.

lld/trunk/ELF/LinkerScript.cpp

 }
 
 template <class ELFT>
 void LinkerScript<ELFT>::discard(ArrayRef<InputSectionBase<ELFT> *> V) {
   for (InputSectionBase<ELFT> *S : V) {
     S->Live = false;
     if (S == In<ELFT>::ShStrTab)
       error("discarding .shstrtab section is not allowed");
-
-    InputSection<ELFT> *IS = dyn_cast<InputSection<ELFT>>(S);
-    if (!IS || IS->DependentSections.empty())
-      continue;
-    discard(IS->DependentSections);
+    discard(S->DependentSections);
   }
 }
 
 template <class ELFT>
 std::vector<InputSectionBase<ELFT> *>
 LinkerScript<ELFT>::createInputSectionList(OutputSectionCommand &OutCmd) {
   std::vector<InputSectionBase<ELFT> *> Ret;