[lldb][DWARFASTParserClang][NFC] Factor out unnamed bitfield creation into helper (llvm#108196)

This logic will need adjusting soon for
llvm#108155

This patch pulls out the logic for detecting/creating unnamed bitfields
out of `ParseSingleMember` to make the latter (in my opinion) more
readable. Otherwise we have a large number of similarly named variables
in scope.

(cherry picked from commit f0c6d30)

Author: Michael137

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

@@ -3024,7 +3024,6 @@ void DWARFASTParserClang::ParseSingleMember(
   }
 
   const uint64_t character_width = 8;
-  const uint64_t word_width = 32;
   CompilerType member_clang_type = member_type->GetLayoutCompilerType();
 
   const auto accessibility = attrs.accessibility == eAccessNone
@@ -3092,40 +3091,9 @@ void DWARFASTParserClang::ParseSingleMember(
       detect_unnamed_bitfields =
           die.GetCU()->Supports_unnamed_objc_bitfields();
 
-    if (detect_unnamed_bitfields) {
-      std::optional<FieldInfo> unnamed_field_info;
-      uint64_t last_field_end =
-          last_field_info.bit_offset + last_field_info.bit_size;
-
-      if (!last_field_info.IsBitfield()) {
-        // The last field was not a bit-field...
-        // but if it did take up the entire word then we need to extend
-        // last_field_end so the bit-field does not step into the last
-        // fields padding.
-        if (last_field_end != 0 && ((last_field_end % word_width) != 0))
-          last_field_end += word_width - (last_field_end % word_width);
-      }
-
-      if (ShouldCreateUnnamedBitfield(last_field_info, last_field_end,
-                                      this_field_info, layout_info)) {
-        unnamed_field_info = FieldInfo{};
-        unnamed_field_info->bit_size =
-            this_field_info.bit_offset - last_field_end;
-        unnamed_field_info->bit_offset = last_field_end;
-      }
-
-      if (unnamed_field_info) {
-        clang::FieldDecl *unnamed_bitfield_decl =
-            TypeSystemClang::AddFieldToRecordType(
-                class_clang_type, llvm::StringRef(),
-                m_ast.GetBuiltinTypeForEncodingAndBitSize(eEncodingSint,
-                                                          word_width),
-                accessibility, unnamed_field_info->bit_size);
-
-        layout_info.field_offsets.insert(std::make_pair(
-            unnamed_bitfield_decl, unnamed_field_info->bit_offset));
-      }
-    }
+    if (detect_unnamed_bitfields)
+      AddUnnamedBitfieldToRecordTypeIfNeeded(layout_info, class_clang_type,
+                                             last_field_info, this_field_info);
 
     last_field_info = this_field_info;
     last_field_info.SetIsBitfield(true);
@@ -3937,6 +3905,43 @@ bool DWARFASTParserClang::ShouldCreateUnnamedBitfield(
   return true;
 }
 
+void DWARFASTParserClang::AddUnnamedBitfieldToRecordTypeIfNeeded(
+    ClangASTImporter::LayoutInfo &class_layout_info,
+    const CompilerType &class_clang_type, const FieldInfo &previous_field,
+    const FieldInfo &current_field) {
+  // TODO: get this value from target
+  const uint64_t word_width = 32;
+  uint64_t last_field_end = previous_field.bit_offset + previous_field.bit_size;
+
+  if (!previous_field.IsBitfield()) {
+    // The last field was not a bit-field...
+    // but if it did take up the entire word then we need to extend
+    // last_field_end so the bit-field does not step into the last
+    // fields padding.
+    if (last_field_end != 0 && ((last_field_end % word_width) != 0))
+      last_field_end += word_width - (last_field_end % word_width);
+  }
+
+  // Nothing to be done.
+  if (!ShouldCreateUnnamedBitfield(previous_field, last_field_end,
+                                   current_field, class_layout_info))
+    return;
+
+  // Place the unnamed bitfield into the gap between the previous field's end
+  // and the current field's start.
+  const uint64_t unnamed_bit_size = current_field.bit_offset - last_field_end;
+  const uint64_t unnamed_bit_offset = last_field_end;
+
+  clang::FieldDecl *unnamed_bitfield_decl =
+      TypeSystemClang::AddFieldToRecordType(
+          class_clang_type, llvm::StringRef(),
+          m_ast.GetBuiltinTypeForEncodingAndBitSize(eEncodingSint, word_width),
+          lldb::AccessType::eAccessPublic, unnamed_bit_size);
+
+  class_layout_info.field_offsets.insert(
+      std::make_pair(unnamed_bitfield_decl, unnamed_bit_offset));
+}
+
 void DWARFASTParserClang::ParseRustVariantPart(
     DWARFDIE &die, const DWARFDIE &parent_die, CompilerType &class_clang_type,
     const lldb::AccessType default_accesibility,

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

@@ -278,7 +278,7 @@ class DWARFASTParserClang : public lldb_private::plugin::dwarf::DWARFASTParser {
     FieldInfo() = default;
 
     void SetIsBitfield(bool flag) { is_bitfield = flag; }
-    bool IsBitfield() { return is_bitfield; }
+    bool IsBitfield() const { return is_bitfield; }
 
     void SetIsArtificial(bool flag) { is_artificial = flag; }
     bool IsArtificial() const { return is_artificial; }
@@ -330,6 +330,35 @@ class DWARFASTParserClang : public lldb_private::plugin::dwarf::DWARFASTParser {
       FieldInfo const &this_field_info,
       lldb_private::ClangASTImporter::LayoutInfo const &layout_info) const;
 
+  /// Tries to detect whether \ref class_clang_type contained an unnamed
+  /// bit-field between \ref previous_field and \ref current_field, and if
+  /// so, adds a clang::FieldDecl representing that bit-field to
+  /// \ref class_clang_type.
+  ///
+  /// This is necessary because Clang (and GCC) doesn't emit a DW_TAG_member
+  /// entry for unnamed bit-fields. So we derive it (with some exceptions),
+  /// by checking whether there is a gap between where the storage of a
+  /// DW_TAG_member ended and the subsequent DW_TAG_member began.
+  ///
+  /// \param[in,out] layout_info Layout information of all decls parsed by the
+  ///                            current parser. Will contain an entry for
+  ///                            the unnamed bit-field if this function created
+  ///                            one.
+  ///
+  /// \param[in] class_clang_type The RecordType to which the unnamed bit-field
+  ///                             will be added (if any).
+  ///
+  /// \param[in] previous_field FieldInfo of the previous DW_TAG_member
+  ///                           we parsed.
+  ///
+  /// \param[in] current_field FieldInfo of the current DW_TAG_member
+  ///                          being parsed.
+  ///
+  void AddUnnamedBitfieldToRecordTypeIfNeeded(
+      lldb_private::ClangASTImporter::LayoutInfo &class_layout_info,
+      const lldb_private::CompilerType &class_clang_type,
+      const FieldInfo &previous_field, const FieldInfo &current_field);
+
   /// Parses a DW_TAG_APPLE_property DIE and appends the parsed data to the
   /// list of delayed Objective-C properties.
   ///