[RF][HS3] Add name-keyed JSONNode cache for RooAbsaArgs

Looking up by name in the JSON tree is quite slow and happens often
during model import from JSON. Caching the pointers to the JSON nodes
corresponding to the RooAbsArgs (distributions and functions) speeds up
JSON import significantly.

(cherry picked from commit 149cca4)

Author: guitargeek

roofit/hs3/inc/RooFitHS3/RooJSONFactoryWSTool.h

@@ -23,6 +23,7 @@
 #include <map>
 #include <stdexcept>
 #include <set>
+#include <unordered_map>
 
 namespace RooFit {
 namespace JSONIO {
@@ -253,5 +254,12 @@ class RooJSONFactoryWSTool {
    std::unique_ptr<RooFit::JSONIO::Detail::Domains> _domains;
    std::vector<RooAbsArg const *> _serversToExport;
    std::vector<RooAbsArg const *> _serversToDelete;
+
+   // Name-keyed indices over the top-level "functions" and "distributions"
+   // sequences of the input JSON. Built once at the start of importAllNodes()
+   // so that requestImpl() lookups become O(1) instead of an O(N) scan over
+   // every sibling node.
+   std::unordered_map<std::string, RooFit::Detail::JSONNode const *> _functionsByName;
+   std::unordered_map<std::string, RooFit::Detail::JSONNode const *> _distributionsByName;
 };
 #endif

roofit/hs3/src/RooJSONFactoryWSTool.cxx

@@ -924,12 +924,11 @@ RooAbsPdf *RooJSONFactoryWSTool::requestImpl<RooAbsPdf>(const std::string &objna
 {
    if (RooAbsPdf *retval = _workspace.pdf(objname))
       return retval;
-   if (const auto &distributionsNode = _rootnodeInput->find("distributions")) {
-      if (const auto &child = findNamedChild(*distributionsNode, objname)) {
-         this->importFunction(*child, true);
-         if (RooAbsPdf *retval = _workspace.pdf(objname))
-            return retval;
-      }
+   auto it = _distributionsByName.find(objname);
+   if (it != _distributionsByName.end()) {
+      this->importFunction(*it->second, true);
+      if (RooAbsPdf *retval = _workspace.pdf(objname))
+         return retval;
    }
    return nullptr;
 }
@@ -945,12 +944,11 @@ RooAbsReal *RooJSONFactoryWSTool::requestImpl<RooAbsReal>(const std::string &obj
       return pdf;
    if (RooRealVar *var = requestImpl<RooRealVar>(objname))
       return var;
-   if (const auto &functionNode = _rootnodeInput->find("functions")) {
-      if (const auto &child = findNamedChild(*functionNode, objname)) {
-         this->importFunction(*child, true);
-         if (RooAbsReal *retval = _workspace.function(objname))
-            return retval;
-      }
+   auto it = _functionsByName.find(objname);
+   if (it != _functionsByName.end()) {
+      this->importFunction(*it->second, true);
+      if (RooAbsReal *retval = _workspace.function(objname))
+         return retval;
    }
    return nullptr;
 }
@@ -2175,6 +2173,31 @@ void RooJSONFactoryWSTool::importAllNodes(const JSONNode &n)
 
    _attributesNode = findRooFitInternal(*_rootnodeInput, "attributes");
 
+   // Build name-keyed indices over the "functions" and "distributions"
+   // sequences. Without these, every cross-reference resolved during import
+   // (e.g. dependencies of a PiecewiseInterpolation, or factory-expression
+   // arguments) triggers a linear scan over all sibling nodes via
+   // findNamedChild(), which becomes O(N^2) on workspaces with thousands of
+   // entries. Populating the maps up-front turns each lookup into O(1).
+   _functionsByName.clear();
+   _distributionsByName.clear();
+   if (auto seq = n.find("functions")) {
+      if (seq->is_seq()) {
+         _functionsByName.reserve(seq->num_children());
+         for (const auto &p : seq->children()) {
+            _functionsByName.emplace(RooJSONFactoryWSTool::name(p), &p);
+         }
+      }
+   }
+   if (auto seq = n.find("distributions")) {
+      if (seq->is_seq()) {
+         _distributionsByName.reserve(seq->num_children());
+         for (const auto &p : seq->children()) {
+            _distributionsByName.emplace(RooJSONFactoryWSTool::name(p), &p);
+         }
+      }
+   }
+
    this->importDependants(n);
 
    if (auto paramPointsNode = n.find("parameter_points")) {
@@ -2239,6 +2262,8 @@ void RooJSONFactoryWSTool::importAllNodes(const JSONNode &n)
 
    _rootnodeInput = nullptr;
    _domains.reset();
+   _functionsByName.clear();
+   _distributionsByName.clear();
 }
 
 /**