[Lldb-commits] [PATCH] D122980: make ConstStringTable use std::unordered_map rather than std::map

[Luboš Luňák via Phabricator via lldb-commits]

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The ordering is not needed, and std::unordered_map is faster (and std::hash for ConstString is trivial). I can measure time spent in the SaveToCache() calls reduced to ~50% during LLDB startup (and a ~25% reduction of the total startup cost).


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D122980

Files:
  lldb/include/lldb/Core/DataFileCache.h
  lldb/include/lldb/Utility/ConstString.h


Index: lldb/include/lldb/Utility/ConstString.h
===================================================================
--- lldb/include/lldb/Utility/ConstString.h
+++ lldb/include/lldb/Utility/ConstString.h
@@ -464,6 +464,16 @@
 }
 } // namespace llvm
 
+namespace std {
+
+template <> struct hash<lldb_private::ConstString> {
+  std::size_t operator()(const lldb_private::ConstString &str) const {
+    return reinterpret_cast<std::size_t>(str.GetCString());
+  }
+};
+
+} // namespace std
+
 LLVM_YAML_IS_SEQUENCE_VECTOR(lldb_private::ConstString)
 
 #endif // LLDB_UTILITY_CONSTSTRING_H
Index: lldb/include/lldb/Core/DataFileCache.h
===================================================================
--- lldb/include/lldb/Core/DataFileCache.h
+++ lldb/include/lldb/Core/DataFileCache.h
@@ -15,6 +15,7 @@
 #include "lldb/lldb-forward.h"
 #include "llvm/Support/Caching.h"
 #include <mutex>
+#include <unordered_map>
 
 namespace lldb_private {
 
@@ -190,7 +191,7 @@
 
 private:
   std::vector<ConstString> m_strings;
-  std::map<ConstString, uint32_t> m_string_to_offset;
+  std::unordered_map<ConstString, uint32_t> m_string_to_offset;
   /// Skip one byte to start the string table off with an empty string.
   uint32_t m_next_offset = 1;
 };


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