minor nits, made a test single threaded. I think technically speaking it's not legal

Author: ayermolo

llvm/include/llvm/DebugInfo/DWARF/DWARFAcceleratorTable.h

@@ -775,7 +775,7 @@ class DWARFDebugNames : public DWARFAcceleratorTable {
     using value_type = NameTableEntry;
     using difference_type = uint32_t;
     using pointer = NameTableEntry *;
-    using reference = NameTableEntry;
+    using reference = NameTableEntry; // We return entries by value.
 
     /// Creates an iterator whose initial position is name CurrentName in
     /// CurrentIndex.

llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp

@@ -38,7 +38,6 @@
 #include "llvm/Support/raw_ostream.h"
 #include <map>
 #include <set>
-#include <unordered_set>
 #include <vector>
 
 using namespace llvm;
@@ -1227,7 +1226,7 @@ void DWARFVerifier::verifyDebugNamesCULists(const DWARFDebugNames &AccelTable) {
   DenseMap<uint64_t, uint64_t> CUMap;
   CUMap.reserve(DCtx.getNumCompileUnits());
 
-  std::unordered_set<uint64_t> CUOffsets;
+  DenseSet<uint64_t> CUOffsets;
   for (const auto &CU : DCtx.compile_units())
     CUOffsets.insert(CU->getOffset());
 
@@ -1523,8 +1522,7 @@ static SmallVector<std::string, 3> getNames(const DWARFDie &DIE,
                                             bool IncludeObjCNames = true,
                                             bool IncludeLinkageName = true) {
   SmallVector<std::string, 3> Result;
-  const char *Str = DIE.getShortName();
-  if (Str) {
+  if (const char *Str = DIE.getShortName()) {
     StringRef Name(Str);
     Result.emplace_back(Name);
     if (IncludeStrippedTemplateNames) {
@@ -1949,8 +1947,8 @@ static void extractCUsTus(DWARFContext &DCtx) {
   for (const auto &CU : DCtx.compile_units()) {
     if (!(CU->getVersion() >= 5 && CU->getDWOId()))
       continue;
-    DWARFUnit *NonSkeletonUnit = CU->getNonSkeletonUnitDIE().getDwarfUnit();
-    DWARFContext &NonSkeletonContext = NonSkeletonUnit->getContext();
+    DWARFContext &NonSkeletonContext =
+        CU->getNonSkeletonUnitDIE().getDwarfUnit()->getContext();
     // Iterates over CUs and TUs.
     for (auto &CUTU : NonSkeletonContext.dwo_units()) {
       CUTU->getUnitDIE();

llvm/test/tools/llvm-dwarfdump/X86/verify_no_linkage_name.s

@@ -1,6 +1,8 @@
 # This test generates a DW_TAG_structure_type with a linkage name. This linkage
 # name will not be part of the accelerator table and the verifier should not
 # complain about this.
+# Technically speaking this test is invalid because .debug_names is a DWARF 5 feature.
+# In this test the accelerator table is referencing DWARF4.
 #
 # DW_TAG_structure_type
 #   DW_AT_name    ("C")
@@ -9,7 +11,7 @@
 # RUN: llvm-mc %s -filetype obj -triple x86_64-unknown-linux-gnu -o %t.o
 # RUN: llvm-dwarfdump -debug-info %t.o | FileCheck %s
 # RUN: llvm-dwarfdump -debug-names %t.o | FileCheck %s --check-prefix ACCEL
-# RUN: llvm-dwarfdump -verify -debug-names %t.o
+# RUN: llvm-dwarfdump -verify --verify-num-threads 1 -debug-names %t.o
 
 # CHECK: DW_AT_name    ("Bool")
 # CHECK-NEXT: DW_AT_linkage_name    ("$SSbD")