Simplify and optimize .debug_names and removed dead TU code

Author: MaskRay

lld/ELF/DWARF.cpp

@@ -40,7 +40,7 @@ template <class ELFT> LLDDwarfObj<ELFT>::LLDDwarfObj(ObjFile<ELFT> *obj) {
                 .Case(".debug_gnu_pubtypes", &gnuPubtypesSection)
                 .Case(".debug_line", &lineSection)
                 .Case(".debug_loclists", &loclistsSection)
-                .Case(".debug_names", &debugNamesSection)
+                .Case(".debug_names", &namesSection)
                 .Case(".debug_ranges", &rangesSection)
                 .Case(".debug_rnglists", &rnglistsSection)
                 .Case(".debug_str_offsets", &strOffsetsSection)

lld/ELF/DWARF.h

@@ -69,7 +69,7 @@ template <class ELFT> class LLDDwarfObj final : public llvm::DWARFObject {
   }
 
   const LLDDWARFSection &getNamesSection() const override {
-    return debugNamesSection;
+    return namesSection;
   }
 
   StringRef getFileName() const override { return ""; }
@@ -94,12 +94,12 @@ template <class ELFT> class LLDDwarfObj final : public llvm::DWARFObject {
   LLDDWARFSection gnuPubtypesSection;
   LLDDWARFSection infoSection;
   LLDDWARFSection loclistsSection;
+  LLDDWARFSection namesSection;
   LLDDWARFSection rangesSection;
   LLDDWARFSection rnglistsSection;
   LLDDWARFSection strOffsetsSection;
   LLDDWARFSection lineSection;
   LLDDWARFSection addrSection;
-  LLDDWARFSection debugNamesSection;
   StringRef abbrevSection;
   StringRef strSection;
   StringRef lineStrSection;