Speedup collecting DWARF attribute values

[dmantipov]

Summary

Try to speedup collecting DWARF attribute values by using emplace_back() to avoid extra calls to copy and/or move constructors.

[aprantl]

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

83

We usually don't prefix constructor arguments. Most LLDB code would write this as
m_cu(cu) for classes and cu(cu) for structs.

[shafik]

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

83

Why not drop the prefixes all together? I don't see what they add here.

[dmantipov]

Drop prefixes and tweak the style to match clang-format requirements.

[dmantipov]

Superseded with https://reviews.llvm.org/D87675.

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

   DWARFAttributes();
   ~DWARFAttributes();
 
-  void Append(const DWARFUnit *cu, dw_offset_t attr_die_offset,
-              dw_attr_t attr, dw_form_t form);
+  void Append(const DWARFUnit *cu, dw_offset_t attr_die_offset, dw_attr_t attr,
+              dw_form_t form) {
+    m_infos.emplace_back(cu, attr_die_offset, attr, form);
+  }
   const DWARFUnit *CompileUnitAtIndex(uint32_t i) const {
     return m_infos[i].cu;
   }

                                 // case we have DW_FORM_ref_addr values
     dw_offset_t die_offset;
     DWARFAttribute attr;
+
+    AttributeValue(const DWARFUnit *cu, dw_offset_t die_offset, dw_attr_t attr,
+                   dw_form_t form)
+      : cu(cu), die_offset(die_offset),
+        attr(attr, form, DWARFFormValue::ValueType()) {}
   };
   typedef llvm::SmallVector<AttributeValue, 8> collection;
   collection m_infos;

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

   return UINT32_MAX;
 }
 
-void DWARFAttributes::Append(const DWARFUnit *cu, dw_offset_t attr_die_offset,
-                             dw_attr_t attr, dw_form_t form) {
-  AttributeValue attr_value = {
-      cu, attr_die_offset, {attr, form, DWARFFormValue::ValueType()}};
-  m_infos.push_back(attr_value);
-}
-
 bool DWARFAttributes::ExtractFormValueAtIndex(
     uint32_t i, DWARFFormValue &form_value) const {
   const DWARFUnit *cu = CompileUnitAtIndex(i);