[Lldb-commits] [lldb] d043ec8 - [lldb] Avoid trie prefix recompuation (NFC) (#200026)

[via lldb-commits]

Author: Dave Lee
Date: 2026-05-29T09:02:33-07:00
New Revision: d043ec846b79e30b8de88e601e8c9e36eee771eb

URL: https://github.com/llvm/llvm-project/commit/d043ec846b79e30b8de88e601e8c9e36eee771eb
DIFF: https://github.com/llvm/llvm-project/commit/d043ec846b79e30b8de88e601e8c9e36eee771eb.diff

LOG: [lldb] Avoid trie prefix recompuation (NFC) (#200026)

Avoid O(depth) string concatenations for every symbol in the Mach-O
exports trie.

This change uses a string to track the current trie prefix, instead of a
vector of substrings. Instead of pushing and popping on the vector, the
string is appended and truncated.

Assisted-by: claude

Added: 
    

Modified: 
    lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp

Removed: 
    


################################################################################
diff  --git a/lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp b/lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
index 814eb58b7b9b8..9fe9af84ffcbc 100644
--- a/lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
+++ b/lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
@@ -1997,7 +1997,7 @@ struct TrieEntryWithOffset {
 
 static bool ParseTrieEntries(DataExtractor &data, lldb::offset_t offset,
                              const bool is_arm, addr_t text_seg_base_addr,
-                             std::vector<llvm::StringRef> &nameSlices,
+                             std::string &prefix,
                              std::set<lldb::addr_t> &resolver_addresses,
                              std::vector<TrieEntryWithOffset> &reexports,
                              std::vector<TrieEntryWithOffset> &ext_symbols) {
@@ -2043,14 +2043,9 @@ static bool ParseTrieEntries(DataExtractor &data, lldb::offset_t offset,
       add_this_entry = true;
     }
     if (add_this_entry) {
-      std::string name;
-      if (!nameSlices.empty()) {
-        for (auto name_slice : nameSlices)
-          name.append(name_slice.data(), name_slice.size());
-      }
-      if (name.size() > 1) {
+      if (prefix.size() > 1) {
         // Skip the leading '_'
-        e.entry.name.SetCStringWithLength(name.c_str() + 1, name.size() - 1);
+        e.entry.name.SetString(llvm::StringRef(prefix).drop_front());
       }
       if (import_name) {
         // Skip the leading '_'
@@ -2071,19 +2066,19 @@ static bool ParseTrieEntries(DataExtractor &data, lldb::offset_t offset,
   const uint8_t childrenCount = data.GetU8(&children_offset);
   for (uint8_t i = 0; i < childrenCount; ++i) {
     const char *cstr = data.GetCStr(&children_offset);
-    if (cstr)
-      nameSlices.push_back(llvm::StringRef(cstr));
-    else
+    if (!cstr)
       return false; // Corrupt data
+    const size_t prevSize = prefix.size();
+    prefix.append(cstr);
     lldb::offset_t childNodeOffset = data.GetULEB128(&children_offset);
     if (childNodeOffset) {
       if (!ParseTrieEntries(data, childNodeOffset, is_arm, text_seg_base_addr,
-                            nameSlices, resolver_addresses, reexports,
+                            prefix, resolver_addresses, reexports,
                             ext_symbols)) {
         return false;
       }
     }
-    nameSlices.pop_back();
+    prefix.resize(prevSize);
   }
   return true;
 }
@@ -2659,9 +2654,9 @@ void ObjectFileMachO::ParseSymtab(Symtab &symtab) {
     lldb::addr_t text_segment_file_addr = LLDB_INVALID_ADDRESS;
     if (text_segment_sp)
       text_segment_file_addr = text_segment_sp->GetFileAddress();
-    std::vector<llvm::StringRef> nameSlices;
-    ParseTrieEntries(dyld_trie_data, 0, is_arm, text_segment_file_addr,
-                     nameSlices, resolver_addresses, reexport_trie_entries,
+    std::string prefix;
+    ParseTrieEntries(dyld_trie_data, 0, is_arm, text_segment_file_addr, prefix,
+                     resolver_addresses, reexport_trie_entries,
                      external_sym_trie_entries);
   }