diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/libexpr/nixexpr.cc | 2 | ||||
| -rw-r--r-- | src/libexpr/symbol-table.hh | 21 |
2 files changed, 15 insertions, 8 deletions
diff --git a/src/libexpr/nixexpr.cc b/src/libexpr/nixexpr.cc index a75357871..640c44c01 100644 --- a/src/libexpr/nixexpr.cc +++ b/src/libexpr/nixexpr.cc @@ -473,7 +473,7 @@ string ExprLambda::showNamePos() const size_t SymbolTable::totalSize() const { size_t n = 0; - for (auto & i : symbols) + for (auto & i : store) n += i.size(); return n; } diff --git a/src/libexpr/symbol-table.hh b/src/libexpr/symbol-table.hh index 4eb6dac81..a090ebae5 100644 --- a/src/libexpr/symbol-table.hh +++ b/src/libexpr/symbol-table.hh @@ -1,7 +1,8 @@ #pragma once +#include <list> #include <map> -#include <unordered_set> +#include <unordered_map> #include "types.hh" @@ -70,15 +71,21 @@ public: class SymbolTable { private: - typedef std::unordered_set<string> Symbols; - Symbols symbols; + std::unordered_map<std::string_view, Symbol> symbols; + std::list<string> store; public: Symbol create(std::string_view s) { - // FIXME: avoid allocation if 's' already exists in the symbol table. - std::pair<Symbols::iterator, bool> res = symbols.emplace(std::string(s)); - return Symbol(&*res.first); + // Most symbols are looked up more than once, so we trade off insertion performance + // for lookup performance. + // TODO: could probably be done more efficiently with transparent Hash and Equals + // on the original implementation using unordered_set + auto it = symbols.find(s); + if (it != symbols.end()) return it->second; + + const string & rawSym = store.emplace_back(s); + return symbols.emplace(rawSym, Symbol(&rawSym)).first->second; } size_t size() const @@ -91,7 +98,7 @@ public: template<typename T> void dump(T callback) { - for (auto & s : symbols) + for (auto & s : store) callback(s); } }; |