RFC 1/3: Unify src<->dst DWARFASTParser for CopyUniqueClassMethodTypes()

[jankratochvil]

Summary

This patchset is removing non-DWARF code from DWARFUnit as discussed with @labath.
For removing the dependency on DWARFDIE.GetCU() (D70647) I have found I can no longer find two different parsers in this case.
IIUC it would mean DW_AT_language is different between the defining and declaring DIE tree - which can happen (and lldbassert in this patch would fail then - this lldbassert is removed in the future patch anyway) but it would be a buggy DWARF in such case.
I do not plan to check it in yet. I plan to finish it for use by DWZ patchset first (D40474 et al.). Asking whether this is a good way forward.

[labath]

@shafik or @teemperor will know more about this.

[teemperor]

I think it's possible that for example with -gmodules we have multiple ClangASTContext's (and therefore multiple DWARFASTParserClang), but the only place where we call this function seems to only concerned about a single SymbolFileDWARF so this seems safe.

[jankratochvil]

This refactorization is no longer needed as I am abandoning D70647 to choose a different way.

lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp

for (idx = 0; idx < src_size; ++idx) {
                 "but 0x%8.8x (%s) names didn't match 0x%8.8x (%s)",
                 src_class_die.GetOffset(), dst_class_die.GetOffset(),
                 src_die.GetOffset(), src_name, dst_die.GetOffset(), dst_name);
 
       fast_path = false;
     }
   }
 
-  DWARFASTParserClang *src_dwarf_ast_parser =
+  DWARFASTParserClang *dwarf_ast_parser =
       (DWARFASTParserClang *)src_die.GetDWARFParser();
-  DWARFASTParserClang *dst_dwarf_ast_parser =
-      (DWARFASTParserClang *)dst_die.GetDWARFParser();
+  lldbassert(dwarf_ast_parser ==
+             (DWARFASTParserClang *)dst_die.GetDWARFParser());
 
   // Now do the work of linking the DeclContexts and Types.
   if (fast_path) {
     // We can do this quickly.  Just run across the tables index-for-index
     // since we know each node has matching names and tags.
     for (idx = 0; idx < src_size; ++idx) {
       src_die = src_name_to_die.GetValueAtIndexUnchecked(idx);
       dst_die = dst_name_to_die.GetValueAtIndexUnchecked(idx);
 
       clang::DeclContext *src_decl_ctx =
-          src_dwarf_ast_parser->m_die_to_decl_ctx[src_die.GetDIE()];
+          dwarf_ast_parser->m_die_to_decl_ctx[src_die.GetDIE()];
       if (src_decl_ctx) {
         LLDB_LOGF(log, "uniquing decl context %p from 0x%8.8x for 0x%8.8x",
                   static_cast<void *>(src_decl_ctx), src_die.GetOffset(),
                   dst_die.GetOffset());
-        dst_dwarf_ast_parser->LinkDeclContextToDIE(src_decl_ctx, dst_die);
+        dwarf_ast_parser->LinkDeclContextToDIE(src_decl_ctx, dst_die);
       } else {
         LLDB_LOGF(log,
                   "warning: tried to unique decl context from 0x%8.8x for "
                   "0x%8.8x, but none was found",
                   src_die.GetOffset(), dst_die.GetOffset());
       }
 
       Type *src_child_type =
if (!src_name_to_die.IsEmpty() && !dst_name_to_die.IsEmpty()) {
 
       for (idx = 0; idx < dst_size; ++idx) {
         ConstString dst_name = dst_name_to_die.GetCStringAtIndex(idx);
         dst_die = dst_name_to_die.GetValueAtIndexUnchecked(idx);
         src_die = src_name_to_die.Find(dst_name, DWARFDIE());
 
         if (src_die && (src_die.Tag() == dst_die.Tag())) {
           clang::DeclContext *src_decl_ctx =
-              src_dwarf_ast_parser->m_die_to_decl_ctx[src_die.GetDIE()];
+              dwarf_ast_parser->m_die_to_decl_ctx[src_die.GetDIE()];
           if (src_decl_ctx) {
             LLDB_LOGF(log, "uniquing decl context %p from 0x%8.8x for 0x%8.8x",
                       static_cast<void *>(src_decl_ctx), src_die.GetOffset(),
                       dst_die.GetOffset());
-            dst_dwarf_ast_parser->LinkDeclContextToDIE(src_decl_ctx, dst_die);
+            dwarf_ast_parser->LinkDeclContextToDIE(src_decl_ctx, dst_die);
           } else {
             LLDB_LOGF(log,
                       "warning: tried to unique decl context from 0x%8.8x "
                       "for 0x%8.8x, but none was found",
                       src_die.GetOffset(), dst_die.GetOffset());
           }
 
           Type *src_child_type =
for (idx = 0; idx < src_size_artificial; ++idx) {
           src_name_to_die_artificial.GetCStringAtIndex(idx);
       src_die = src_name_to_die_artificial.GetValueAtIndexUnchecked(idx);
       dst_die =
           dst_name_to_die_artificial.Find(src_name_artificial, DWARFDIE());
 
       if (dst_die) {
         // Both classes have the artificial types, link them
         clang::DeclContext *src_decl_ctx =
-            src_dwarf_ast_parser->m_die_to_decl_ctx[src_die.GetDIE()];
+            dwarf_ast_parser->m_die_to_decl_ctx[src_die.GetDIE()];
         if (src_decl_ctx) {
           LLDB_LOGF(log, "uniquing decl context %p from 0x%8.8x for 0x%8.8x",
                     static_cast<void *>(src_decl_ctx), src_die.GetOffset(),
                     dst_die.GetOffset());
-          dst_dwarf_ast_parser->LinkDeclContextToDIE(src_decl_ctx, dst_die);
+          dwarf_ast_parser->LinkDeclContextToDIE(src_decl_ctx, dst_die);
         } else {
           LLDB_LOGF(log,
                     "warning: tried to unique decl context from 0x%8.8x "
                     "for 0x%8.8x, but none was found",
                     src_die.GetOffset(), dst_die.GetOffset());
         }
 
         Type *src_child_type =