[lldb][SymbolFileDWARF][NFC] Remove unnecessary calls to GetDWARFDeclContext

[felipepiovezan]

The function FindDefinitionTypeForDWARFDeclContext loops over all DIEs corresponding to types with a certain name and compares the context of each found DIE with the context of a target DIE. However, the target DIE never changes throughout this search, and yet we recompute its DeclContext on every iteration of the search. This is wasteful because the method is not exactly free (see DWARFDebugInfoEntry::GetDWARFDeclContextStatic).

[llvmbot]

@llvm/pr-subscribers-lldb

Author: Felipe de Azevedo Piovezan (felipepiovezan)

Changes

The function FindDefinitionTypeForDWARFDeclContext loops over all DIEs corresponding to types with a certain name and compares the context of each found DIE with the context of a target DIE. However, the target DIE never changes throughout this search, and yet we recompute its DeclContext on every iteration of the search. This is wasteful because the method is not exactly free (see DWARFDebugInfoEntry::GetDWARFDeclContextStatic).

---

Full diff: https://github.com/llvm/llvm-project/pull/74523.diff

1 Files Affected:

• (modified) lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp (+3-2)

diff --git a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
index 142d092e6d2ee..d4cc26a3c329b 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
@@ -3120,7 +3120,8 @@ SymbolFileDWARF::FindDefinitionTypeForDWARFDeclContext(const DWARFDIE &die) {
         template_params = dwarf_ast->GetDIEClassTemplateParams(die);
     }
 
-    m_index->GetTypes(GetDWARFDeclContext(die), [&](DWARFDIE type_die) {
+    const DWARFDeclContext die_dwarf_decl_ctx = GetDWARFDeclContext(die);
+    m_index->GetTypes(die_dwarf_decl_ctx, [&](DWARFDIE type_die) {
       // Make sure type_die's language matches the type system we are
       // looking for. We don't want to find a "Foo" type from Java if we
       // are looking for a "Foo" type for C, C++, ObjC, or ObjC++.
@@ -3184,7 +3185,7 @@ SymbolFileDWARF::FindDefinitionTypeForDWARFDeclContext(const DWARFDIE &die) {
       }
 
       // Make sure the decl contexts match all the way up
-      if (GetDWARFDeclContext(die) != type_dwarf_decl_ctx)
+      if (die_dwarf_decl_ctx != type_dwarf_decl_ctx)
         return true;
 
       Type *resolved_type = ResolveType(type_die, false);