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libexpr/primops: pass the underlying Value of symbols if possible

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Instead of allocating a new Value and copy the symbol string
representation inside of it, we can pass along the underlying Value,
which avoids (garbage collected) allocations.

This results in:

* a ~8 % reduction for `gc.totalBytes` over
  `nixos.ec2.closures.x86_64-linux` for NixOS 24.11. (920MiB → 842MiB)
* a slight reduction in CPU time due to less allocations being performed
  at all

Change-Id: I097f586dbc98f889fbc62d0a5f80c9d76ddedfd2
Signed-off-by: Raito Bezarius <raito@lix.systems>
This commit is contained in:
Raito Bezarius
2025-06-10 13:58:08 +02:00
parent 5e98a2159b
commit ebc8f56b52
1 changed files with 3 additions and 5 deletions
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lix/libexpr/primops.cc
+3 -5
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@@ -1582,7 +1582,7 @@ static void prim_attrNames(EvalState & state, Value * * args, Value & v)
size_t n = 0;
for (auto & i : *args[0]->attrs)
(v.listElems()[n++] = state.ctx.mem.allocValue())->mkString(state.ctx.symbols[i.name]);
v.listElems()[n++] = const_cast<Value *>(state.ctx.symbols[i.name].toValuePtr());
std::sort(v.listElems(), v.listElems() + n,
[](Value * v1, Value * v2) { return strcmp(v1->string.s, v2->string.s) < 0; });
@@ -1881,9 +1881,8 @@ static void prim_mapAttrs(EvalState & state, Value * * args, Value & v)
auto attrs = state.ctx.buildBindings(args[1]->attrs->size());
for (auto & i : *args[1]->attrs) {
Value * vName = state.ctx.mem.allocValue();
Value * vFun2 = state.ctx.mem.allocValue();
vName->mkString(state.ctx.symbols[i.name]);
auto vName = const_cast<Value *>(state.ctx.symbols[i.name].toValuePtr());
vFun2->mkApp(args[0], vName);
attrs.alloc(i.name).mkApp(vFun2, i.value);
}
@@ -1929,8 +1928,7 @@ static void prim_zipAttrsWith(EvalState & state, Value * * args, Value & v)
}
for (auto & attr : *v.attrs) {
auto name = state.ctx.mem.allocValue();
name->mkString(state.ctx.symbols[attr.name]);
auto name = const_cast<Value *>(state.ctx.symbols[attr.name].toValuePtr());
auto call1 = state.ctx.mem.allocValue();
call1->mkApp(args[0], name);
auto call2 = state.ctx.mem.allocValue();