refactor(3p/nix/libexpr): Use range insertion to merge nix::Bindings

Instead of manually iterating over the two bindings to be combined,
this adds a new static method on the Bindings class which merges two
attribute sets by calling the range insertion operator over them.

In some anecdotal tests, this can lead to a ~10% speed bump -
depending on the specific operation.

Change-Id: I5dea03b0589a83a789d3a8a0fc81d0d9e6598371
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1216
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>
This commit is contained in:
Vincent Ambo 2020-07-16 19:31:30 +01:00 committed by tazjin
parent 1ba5aa293b
commit cb3d967508
3 changed files with 25 additions and 18 deletions

View file

@ -33,7 +33,7 @@ void Bindings::push_back(const Attr& attr) {
}
}
size_t Bindings::size() { return attributes_.size(); }
size_t Bindings::size() const { return attributes_.size(); }
bool Bindings::empty() { return attributes_.empty(); }
@ -56,13 +56,6 @@ Bindings::iterator Bindings::begin() { return attributes_.begin(); }
Bindings::iterator Bindings::end() { return attributes_.end(); }
void Bindings::merge(const Bindings& other) {
assert(this != &ZERO_BINDINGS);
for (auto& [key, value] : other.attributes_) {
this->attributes_.insert_or_assign(key, value);
}
}
Bindings* Bindings::NewGC(size_t capacity) {
if (capacity == 0) {
return &ZERO_BINDINGS;
@ -71,6 +64,21 @@ Bindings* Bindings::NewGC(size_t capacity) {
return new (GC) Bindings;
}
Bindings* Bindings::Merge(const Bindings& lhs, const Bindings& rhs) {
auto bindings = NewGC(lhs.size() + rhs.size());
// Values are merged by inserting the entire iterator range of both
// input sets. The right-hand set (the values of which take
// precedence) is inserted *first* because the range insertion
// method does not override values.
bindings->attributes_.insert(rhs.attributes_.cbegin(),
rhs.attributes_.cend());
bindings->attributes_.insert(lhs.attributes_.cbegin(),
lhs.attributes_.cend());
return bindings;
}
void EvalState::mkAttrs(Value& v, size_t capacity) {
clearValue(v);
v.type = tAttrs;

View file

@ -36,8 +36,12 @@ class Bindings {
// collector.
static Bindings* NewGC(size_t capacity = 0);
// Create a new attribute set by merging two others. This is used to
// implement the `//` operator in Nix.
static Bindings* Merge(const Bindings& lhs, const Bindings& rhs);
// Return the number of contained elements.
size_t size();
size_t size() const;
// Is this attribute set empty?
bool empty();
@ -48,13 +52,9 @@ class Bindings {
// Look up a specific element of the attribute set.
iterator find(const Symbol& name);
// TODO
iterator begin();
iterator end();
// Merge values from other into this attribute set.
void merge(const Bindings& other);
// TODO: can callers just iterate?
[[deprecated]] std::vector<const Attr*> lexicographicOrder();

View file

@ -19,6 +19,7 @@
#include "libexpr/eval-inline.hh"
#include "libexpr/function-trace.hh"
#include "libexpr/value.hh"
#include "libstore/derivations.hh"
#include "libstore/download.hh"
#include "libstore/globals.hh"
@ -1240,11 +1241,9 @@ void ExprOpUpdate::eval(EvalState& state, Env& env, Value& dest) {
state.nrOpUpdates++;
state.mkAttrs(dest, v1.attrs->size() + v2.attrs->size());
// Merge the sets, preferring values from the second set.
dest.attrs->merge(*v1.attrs);
dest.attrs->merge(*v2.attrs);
clearValue(dest);
dest.type = tAttrs;
dest.attrs = Bindings::Merge(*v1.attrs, *v2.attrs);
}
void ExprOpConcatLists::eval(EvalState& state, Env& env, Value& v) {