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libexpr: don't allocate additional set in builtins.listToAttrs
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1 changed files with 32 additions and 10 deletions
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@ -2961,25 +2961,47 @@ static void prim_listToAttrs(EvalState & state, const PosIdx pos, Value * * args
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{
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{
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state.forceList(*args[0], pos, "while evaluating the argument passed to builtins.listToAttrs");
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state.forceList(*args[0], pos, "while evaluating the argument passed to builtins.listToAttrs");
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auto attrs = state.buildBindings(args[0]->listSize());
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// Step 1. Sort the name-value attrsets in place using the memory we allocate for the result
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size_t listSize = args[0]->listSize();
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auto & bindings = *state.allocBindings(listSize);
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using ElemPtr = decltype(&bindings[0].value);
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std::set<Symbol> seen;
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for (const auto & [n, v2] : enumerate(args[0]->listItems())) {
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for (auto v2 : args[0]->listItems()) {
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state.forceAttrs(*v2, pos, "while evaluating an element of the list passed to builtins.listToAttrs");
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state.forceAttrs(*v2, pos, "while evaluating an element of the list passed to builtins.listToAttrs");
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auto j = state.getAttr(state.sName, v2->attrs(), "in a {name=...; value=...;} pair");
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auto j = state.getAttr(state.sName, v2->attrs(), "in a {name=...; value=...;} pair");
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auto name = state.forceStringNoCtx(*j->value, j->pos, "while evaluating the `name` attribute of an element of the list passed to builtins.listToAttrs");
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auto name = state.forceStringNoCtx(*j->value, j->pos, "while evaluating the `name` attribute of an element of the list passed to builtins.listToAttrs");
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auto sym = state.symbols.create(name);
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auto sym = state.symbols.create(name);
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if (seen.insert(sym).second) {
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auto j2 = state.getAttr(state.sValue, v2->attrs(), "in a {name=...; value=...;} pair");
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// (ab)use Attr to store a Value * * instead of a Value *, so that we can stabilize the sort using the Value * *
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attrs.insert(sym, j2->value, j2->pos);
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bindings[n] = Attr(sym, std::bit_cast<Value *>(&v2));
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}
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}
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}
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v.mkAttrs(attrs);
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std::sort(&bindings[0], &bindings[listSize], [](const Attr & a, const Attr & b) {
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// Note that .value is actually a Value * * that corresponds to the position in the list
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return a < b || (!(a > b) && std::bit_cast<ElemPtr>(a.value) < std::bit_cast<ElemPtr>(b.value));
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});
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// Step 2. Unpack the bindings in place and skip name-value pairs with duplicate names
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Symbol prev;
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for (size_t n = 0; n < listSize; n++) {
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auto attr = bindings[n];
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if (prev == attr.name) {
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continue;
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}
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// Note that .value is actually a Value * *; see earlier comments
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Value * v2 = *std::bit_cast<ElemPtr>(attr.value);
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auto j = state.getAttr(state.sValue, v2->attrs(), "in a {name=...; value=...;} pair");
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prev = attr.name;
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bindings.push_back({prev, j->value, j->pos});
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}
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// help GC and clear end of allocated array
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for (size_t n = bindings.size(); n < listSize; n++) {
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bindings[n] = Attr{};
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}
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v.mkAttrs(&bindings);
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}
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}
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static RegisterPrimOp primop_listToAttrs({
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static RegisterPrimOp primop_listToAttrs({
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