[lldb][NFCI] Apply IndexEntry to DWARFUnitHeader outside of extraction

I plan on replacing LLDB's DWARFUnitHeader implementation with LLVM's.
LLVM's DWARFUnitHeader::extract applies the DWARFUnitIndex::Entry to a
given DWARFUnitHeader outside of the extraction because the index entry
is only relevant to one place where we may parse DWARFUnitHeaders
(specifically when we're creating a DWARFUnit in a DWO context). To ease
the transition, I've reshaped LLDB's implementation to look closer to
LLVM's.

Reviewed By: aprantl, fdeazeve

Differential Revision: https://reviews.llvm.org/D151919

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

@@ -877,11 +877,37 @@ const DWARFDebugAranges &DWARFUnit::GetFunctionAranges() {
   return *m_func_aranges_up;
 }
 
-llvm::Expected<DWARFUnitHeader>
-DWARFUnitHeader::extract(const DWARFDataExtractor &data,
-                         DIERef::Section section,
-                         lldb_private::DWARFContext &context,
-                         lldb::offset_t *offset_ptr) {
+llvm::Error DWARFUnitHeader::ApplyIndexEntry(
+    const llvm::DWARFUnitIndex::Entry *index_entry) {
+  // We should only be calling this function when the index entry is not set and
+  // we have a valid one to set it to.
+  assert(index_entry);
+  assert(!m_index_entry);
+
+  if (m_abbr_offset)
+    return llvm::createStringError(
+        llvm::inconvertibleErrorCode(),
+        "Package unit with a non-zero abbreviation offset");
+
+  auto *unit_contrib = index_entry->getContribution();
+  if (!unit_contrib || unit_contrib->getLength32() != m_length + 4)
+    return llvm::createStringError(llvm::inconvertibleErrorCode(),
+                                   "Inconsistent DWARF package unit index");
+
+  auto *abbr_entry = index_entry->getContribution(llvm::DW_SECT_ABBREV);
+  if (!abbr_entry)
+    return llvm::createStringError(
+        llvm::inconvertibleErrorCode(),
+        "DWARF package index missing abbreviation column");
+
+  m_abbr_offset = abbr_entry->getOffset();
+  m_index_entry = index_entry;
+  return llvm::Error::success();
+}
+
+llvm::Expected<DWARFUnitHeader> DWARFUnitHeader::extract(
+    const DWARFDataExtractor &data, DIERef::Section section,
+    lldb_private::DWARFContext &context, lldb::offset_t *offset_ptr) {
   DWARFUnitHeader header;
   header.m_offset = *offset_ptr;
   header.m_length = data.GetDWARFInitialLength(offset_ptr);
@@ -905,42 +931,6 @@ DWARFUnitHeader::extract(const DWARFDataExtractor &data,
     header.m_type_offset = data.GetDWARFOffset(offset_ptr);
   }
 
-  if (context.isDwo()) {
-    const llvm::DWARFUnitIndex *Index;
-    if (header.IsTypeUnit()) {
-      Index = &context.GetAsLLVM().getTUIndex();
-      if (*Index)
-        header.m_index_entry = Index->getFromHash(header.m_type_hash);
-    } else {
-      Index = &context.GetAsLLVM().getCUIndex();
-      if (*Index && header.m_version >= 5 && header.m_dwo_id)
-        header.m_index_entry = Index->getFromHash(*header.m_dwo_id);
-    }
-    if (!header.m_index_entry)
-      header.m_index_entry = Index->getFromOffset(header.m_offset);
-  }
-
-  if (header.m_index_entry) {
-    if (header.m_abbr_offset) {
-      return llvm::createStringError(
-          llvm::inconvertibleErrorCode(),
-          "Package unit with a non-zero abbreviation offset");
-    }
-    auto *unit_contrib = header.m_index_entry->getContribution();
-    if (!unit_contrib || unit_contrib->getLength32() != header.m_length + 4) {
-      return llvm::createStringError(llvm::inconvertibleErrorCode(),
-                                     "Inconsistent DWARF package unit index");
-    }
-    auto *abbr_entry =
-        header.m_index_entry->getContribution(llvm::DW_SECT_ABBREV);
-    if (!abbr_entry) {
-      return llvm::createStringError(
-          llvm::inconvertibleErrorCode(),
-          "DWARF package index missing abbreviation column");
-    }
-    header.m_abbr_offset = abbr_entry->getOffset();
-  }
-
   bool length_OK = data.ValidOffset(header.GetNextUnitOffset() - 1);
   bool version_OK = SymbolFileDWARF::SupportedVersion(header.m_version);
   bool addr_size_OK = (header.m_addr_size == 2) || (header.m_addr_size == 4) ||
@@ -970,11 +960,30 @@ DWARFUnit::extract(SymbolFileDWARF &dwarf, user_id_t uid,
                    DIERef::Section section, lldb::offset_t *offset_ptr) {
   assert(debug_info.ValidOffset(*offset_ptr));
 
-  auto expected_header = DWARFUnitHeader::extract(
-      debug_info, section, dwarf.GetDWARFContext(), offset_ptr);
+  DWARFContext &context = dwarf.GetDWARFContext();
+  auto expected_header =
+      DWARFUnitHeader::extract(debug_info, section, context, offset_ptr);
   if (!expected_header)
     return expected_header.takeError();
 
+  if (context.isDwo()) {
+    const llvm::DWARFUnitIndex::Entry *entry = nullptr;
+    const llvm::DWARFUnitIndex &index = expected_header->IsTypeUnit()
+                                            ? context.GetAsLLVM().getTUIndex()
+                                            : context.GetAsLLVM().getCUIndex();
+    if (index) {
+      if (expected_header->IsTypeUnit())
+        entry = index.getFromHash(expected_header->GetTypeHash());
+      else if (auto dwo_id = expected_header->GetDWOId())
+        entry = index.getFromHash(*dwo_id);
+    }
+    if (!entry)
+      entry = index.getFromOffset(expected_header->GetOffset());
+    if (entry)
+      if (llvm::Error err = expected_header->ApplyIndexEntry(entry))
+        return err;
+  }
+
   const llvm::DWARFDebugAbbrev *abbr = dwarf.DebugAbbrev();
   if (!abbr)
     return llvm::make_error<llvm::object::GenericBinaryError>(

lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.h

@@ -76,6 +76,8 @@ class DWARFUnitHeader {
   }
   uint32_t GetNextUnitOffset() const { return m_offset + m_length + 4; }
 
+  llvm::Error ApplyIndexEntry(const llvm::DWARFUnitIndex::Entry *index_entry);
+
   static llvm::Expected<DWARFUnitHeader>
   extract(const lldb_private::DWARFDataExtractor &data, DIERef::Section section,
           lldb_private::DWARFContext &dwarf_context,