[llvm] [LLVM][DWARF] Add support for monolithic types in .debug_names (PR #70515)

[Alexander Yermolovich via llvm-commits]

================
@@ -562,36 +595,58 @@ void llvm::emitDWARF5AccelTable(
     default:
       continue;
     }
-    CUIndex[CU.index()] = Count++;
+    CUIndex[CU.index()] = CUCount++;
     assert(CU.index() == CU.value()->getUniqueID());
     const DwarfCompileUnit *MainCU =
         DD.useSplitDwarf() ? CU.value()->getSkeleton() : CU.value().get();
     CompUnits.push_back(MainCU->getLabelBegin());
   }
 
+  for (const auto &TU : TUSymbols) {
+    TUIndex[TU.UniqueID] = TUCount++;
+    TypeUnits.push_back(TU.Label);
+  }
+
   if (CompUnits.empty())
     return;
 
   Asm->OutStreamer->switchSection(
       Asm->getObjFileLowering().getDwarfDebugNamesSection());
 
   Contents.finalize(Asm, "names");
+  dwarf::Form CUIndexForm =
+      DIEInteger::BestForm(/*IsSigned*/ false, CompUnits.size() - 1);
+  dwarf::Form TUIndexForm =
+      DIEInteger::BestForm(/*IsSigned*/ false, TypeUnits.size() - 1);
   Dwarf5AccelTableWriter<DWARF5AccelTableData>(
-      Asm, Contents, CompUnits,
-      [&](const DWARF5AccelTableData &Entry) {
-        return CUIndex[Entry.getUnitID()];
+      Asm, Contents, CompUnits, TypeUnits,
+      [&](const DWARF5AccelTableData &Entry)
+          -> DWARF5AccelTableEntryReturnType {
+        if (Entry.isTU())
+          return {{TUIndex[Entry.getUnitID()],
+                   {dwarf::DW_IDX_type_unit, TUIndexForm}}};
+        if (CUIndex.size() > 1)
----------------
ayermolo wrote:

For cases where there is only one CU there is no DW_IDX_compile_unit. This is basically the default for non-lto builds since each compilation unit only has one CU.

>From DWARF5 spec page 142:
"6.1.1.3 Per-CU versus Per-Module Indexes
13 In a per-CU index, the CU list may have only a single entry, and index entries may omit
14 the CU attribute."

https://github.com/llvm/llvm-project/pull/70515