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>
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3 changed files with 25 additions and 18 deletions
24
third_party/nix/src/libexpr/attr-set.cc
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24
third_party/nix/src/libexpr/attr-set.cc
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@ -33,7 +33,7 @@ void Bindings::push_back(const Attr& attr) {
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}
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}
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size_t Bindings::size() { return attributes_.size(); }
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size_t Bindings::size() const { return attributes_.size(); }
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bool Bindings::empty() { return attributes_.empty(); }
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@ -56,13 +56,6 @@ Bindings::iterator Bindings::begin() { return attributes_.begin(); }
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Bindings::iterator Bindings::end() { return attributes_.end(); }
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void Bindings::merge(const Bindings& other) {
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assert(this != &ZERO_BINDINGS);
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for (auto& [key, value] : other.attributes_) {
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this->attributes_.insert_or_assign(key, value);
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}
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}
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Bindings* Bindings::NewGC(size_t capacity) {
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if (capacity == 0) {
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return &ZERO_BINDINGS;
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@ -71,6 +64,21 @@ Bindings* Bindings::NewGC(size_t capacity) {
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return new (GC) Bindings;
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}
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Bindings* Bindings::Merge(const Bindings& lhs, const Bindings& rhs) {
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auto bindings = NewGC(lhs.size() + rhs.size());
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// Values are merged by inserting the entire iterator range of both
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// input sets. The right-hand set (the values of which take
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// precedence) is inserted *first* because the range insertion
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// method does not override values.
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bindings->attributes_.insert(rhs.attributes_.cbegin(),
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rhs.attributes_.cend());
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bindings->attributes_.insert(lhs.attributes_.cbegin(),
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lhs.attributes_.cend());
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return bindings;
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}
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void EvalState::mkAttrs(Value& v, size_t capacity) {
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clearValue(v);
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v.type = tAttrs;
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10
third_party/nix/src/libexpr/attr-set.hh
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10
third_party/nix/src/libexpr/attr-set.hh
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@ -36,8 +36,12 @@ class Bindings {
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// collector.
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static Bindings* NewGC(size_t capacity = 0);
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// Create a new attribute set by merging two others. This is used to
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// implement the `//` operator in Nix.
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static Bindings* Merge(const Bindings& lhs, const Bindings& rhs);
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// Return the number of contained elements.
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size_t size();
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size_t size() const;
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// Is this attribute set empty?
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bool empty();
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@ -48,13 +52,9 @@ class Bindings {
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// Look up a specific element of the attribute set.
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iterator find(const Symbol& name);
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// TODO
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iterator begin();
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iterator end();
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// Merge values from other into this attribute set.
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void merge(const Bindings& other);
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// TODO: can callers just iterate?
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[[deprecated]] std::vector<const Attr*> lexicographicOrder();
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9
third_party/nix/src/libexpr/eval.cc
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third_party/nix/src/libexpr/eval.cc
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@ -19,6 +19,7 @@
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#include "libexpr/eval-inline.hh"
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#include "libexpr/function-trace.hh"
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#include "libexpr/value.hh"
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#include "libstore/derivations.hh"
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#include "libstore/download.hh"
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#include "libstore/globals.hh"
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@ -1240,11 +1241,9 @@ void ExprOpUpdate::eval(EvalState& state, Env& env, Value& dest) {
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state.nrOpUpdates++;
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state.mkAttrs(dest, v1.attrs->size() + v2.attrs->size());
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// Merge the sets, preferring values from the second set.
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dest.attrs->merge(*v1.attrs);
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dest.attrs->merge(*v2.attrs);
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clearValue(dest);
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dest.type = tAttrs;
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dest.attrs = Bindings::Merge(*v1.attrs, *v2.attrs);
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}
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void ExprOpConcatLists::eval(EvalState& state, Env& env, Value& v) {
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