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Fix accidental O(n^2 * log n) performance in NixRepl::addAttrsToScope

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Only sort once, after adding all of the attrs first. This reduces my
`nix repl '<nixpkgs>'` loading time from 1.07s to 103ms.

Fixes #5823
This commit is contained in:
Yorick van Pelt 2021-12-27 13:18:55 +01:00
parent af553b2090
commit a4ab0a74d9
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GPG key ID: D8D3CC6D951384DE
2 changed files with 17 additions and 2 deletions
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7
src/libexpr/nixexpr.hh
View file

@ -368,6 +368,13 @@ struct StaticEnv
[](const Vars::value_type & a, const Vars::value_type & b) { return a.first < b.first; });
}
void deduplicate()
{
const auto last = std::unique(vars.begin(), vars.end(),
[] (const Vars::value_type & a, const Vars::value_type & b) { return a.first == b.first; });
vars.erase(last, vars.end());
}
Vars::const_iterator find(const Symbol & name) const
{
Vars::value_type key(name, 0);

12
src/nix/repl.cc
View file

@ -661,8 +661,16 @@ void NixRepl::reloadFiles()
void NixRepl::addAttrsToScope(Value & attrs)
{
state->forceAttrs(attrs);
for (auto & i : *attrs.attrs)
addVarToScope(i.name, *i.value);
if (displ + attrs.attrs->size() >= envSize)
throw Error("environment full; cannot add more variables");
for (auto & i : *attrs.attrs) {
staticEnv.vars.emplace_back(i.name, displ);
env->values[displ++] = i.value;
varNames.insert((string) i.name);
}
staticEnv.sort();
staticEnv.deduplicate();
notice("Added %1% variables.", attrs.attrs->size());
}