[RF] Implement the EvalBackend("codegen_no_grad") option

This is done by adding a new constructor flag to the RooFuncWrapper
whether the gradient should be compiled or not.

roofit/roofitcore/inc/RooFuncWrapper.h

@@ -29,18 +29,18 @@ class RooSimultaneous;
 class RooFuncWrapper final : public RooAbsReal {
 public:
    RooFuncWrapper(const char *name, const char *title, std::string const &funcBody, RooArgSet const &paramSet,
-                  const RooAbsData *data = nullptr, RooSimultaneous const *simPdf = nullptr);
+                  const RooAbsData *data, RooSimultaneous const *simPdf, bool createGradient);
 
    RooFuncWrapper(const char *name, const char *title, RooAbsReal const &obj, RooArgSet const &normSet,
-                  const RooAbsData *data = nullptr, RooSimultaneous const *simPdf = nullptr);
+                  const RooAbsData *data, RooSimultaneous const *simPdf, bool createGradient);
 
    RooFuncWrapper(const RooFuncWrapper &other, const char *name = nullptr);
 
    TObject *clone(const char *newname) const override { return new RooFuncWrapper(*this, newname); }
 
    double defaultErrorLevel() const override { return 0.5; }
 
-   bool hasGradient() const override { return true; }
+   bool hasGradient() const override { return _hasGradient; }
    void gradient(double *out) const override;
 
    void gradient(const double *x, double *g) const;
@@ -65,7 +65,7 @@ class RooFuncWrapper final : public RooAbsReal {
    void loadParamsAndData(std::string funcName, RooAbsArg const *head, RooArgSet const &paramSet,
                           const RooAbsData *data, RooSimultaneous const *simPdf);
 
-   void declareAndDiffFunction(std::string funcName, std::string const &funcBody);
+   void declareAndDiffFunction(std::string funcName, std::string const &funcBody, bool createGradient);
 
    void buildFuncAndGradFunctors();
 
@@ -81,6 +81,7 @@ class RooFuncWrapper final : public RooAbsReal {
    RooListProxy _params;
    Func _func;
    Grad _grad;
+   bool _hasGradient = false;
    mutable std::vector<double> _gradientVarBuffer;
    std::vector<double> _observables;
    std::map<RooFit::Detail::DataKey, ObsInfo> _obsInfos;

roofit/roofitcore/inc/RooGlobalFunc.h

@@ -223,12 +223,12 @@ RooCmdArg Parallelize(int nWorkers) ;
 RooCmdArg ModularL(bool flag=false) ;
 RooCmdArg TimingAnalysis(bool timingAnalysis) ;
 
-RooCmdArg BatchMode(std::string const& batchMode="cpu");
-// The const char * overload is necessary, otherwise the compiler will cast a
-// C-Style string to a bool and choose the BatchMode(bool) overload if one
-// calls for example BatchMode("off").
-inline RooCmdArg BatchMode(const char * batchMode) { return BatchMode(std::string(batchMode)); }
-inline RooCmdArg BatchMode(bool batchModeOn) { return BatchMode(batchModeOn ? "cpu" : "off"); }
+//RooCmdArg BatchMode(std::string const& batchMode="cpu");
+//// The const char * overload is necessary, otherwise the compiler will cast a
+//// C-Style string to a bool and choose the BatchMode(bool) overload if one
+//// calls for example BatchMode("off").
+//inline RooCmdArg BatchMode(const char * batchMode) { return BatchMode(std::string(batchMode)); }
+//inline RooCmdArg BatchMode(bool batchModeOn) { return BatchMode(batchModeOn ? "cpu" : "off"); }
 
 RooCmdArg IntegrateBins(double precision);
 

roofit/roofitcore/src/RooAbsPdf.cxx

@@ -1221,11 +1221,13 @@ std::unique_ptr<RooAbsReal> RooAbsPdf::createNLLImpl(RooAbsData& data, const Roo
 
     std::unique_ptr<RooAbsReal> nllWrapper;
 
-    if(evalBackend == RooFit::EvalBackend::Value::Codegen) {
+    if(evalBackend == RooFit::EvalBackend::Value::Codegen || evalBackend == RooFit::EvalBackend::Value::CodegenNoGrad) {
        static int iFuncWrapper = 0;
        std::string wrapperName = "nll_func_wrapper_" + std::to_string(iFuncWrapper++);
+       bool createGradient = evalBackend == RooFit::EvalBackend::Value::Codegen;
+       auto simPdf = dynamic_cast<RooSimultaneous const *>(pdfClone.get());
        nllWrapper = std::make_unique<RooFuncWrapper>(wrapperName.c_str(), wrapperName.c_str(), *nll, normSet, &data,
-                                                     dynamic_cast<RooSimultaneous const *>(pdfClone.get()));
+                                                     simPdf, createGradient);
     } else {
       auto evaluator = std::make_unique<RooFit::Evaluator>(*nll, evalBackend == RooFit::EvalBackend::Value::Cuda);
       nllWrapper = std::make_unique<RooEvaluatorWrapper>(*nll,

roofit/roofitcore/src/RooFuncWrapper.cxx

@@ -24,20 +24,20 @@
 #include <TSystem.h>
 
 RooFuncWrapper::RooFuncWrapper(const char *name, const char *title, std::string const &funcBody,
-                               RooArgSet const &paramSet, const RooAbsData *data /*=nullptr*/,
-                               RooSimultaneous const *simPdf)
-   : RooAbsReal{name, title}, _params{"!params", "List of parameters", this}
+                               RooArgSet const &paramSet, const RooAbsData *data, RooSimultaneous const *simPdf,
+                               bool createGradient)
+   : RooAbsReal{name, title}, _params{"!params", "List of parameters", this}, _hasGradient{createGradient}
 {
    // Declare the function and create its derivative.
-   declareAndDiffFunction(name, funcBody);
+   declareAndDiffFunction(name, funcBody, createGradient);
 
    // Load the parameters and observables.
    loadParamsAndData(name, nullptr, paramSet, data, simPdf);
 }
 
 RooFuncWrapper::RooFuncWrapper(const char *name, const char *title, RooAbsReal const &obj, RooArgSet const &normSet,
-                               const RooAbsData *data /*=nullptr*/, RooSimultaneous const *simPdf)
-   : RooAbsReal{name, title}, _params{"!params", "List of parameters", this}
+                               const RooAbsData *data, RooSimultaneous const *simPdf, bool createGradient)
+   : RooAbsReal{name, title}, _params{"!params", "List of parameters", this}, _hasGradient{createGradient}
 {
    std::string func;
 
@@ -60,14 +60,15 @@ RooFuncWrapper::RooFuncWrapper(const char *name, const char *title, RooAbsReal c
    func = buildCode(*pdf);
 
    // Declare the function and create its derivative.
-   declareAndDiffFunction(name, func);
+   declareAndDiffFunction(name, func, createGradient);
 }
 
 RooFuncWrapper::RooFuncWrapper(const RooFuncWrapper &other, const char *name)
    : RooAbsReal(other, name),
      _params("!params", this, other._params),
      _func(other._func),
      _grad(other._grad),
+     _hasGradient(other._hasGradient),
      _gradientVarBuffer(other._gradientVarBuffer),
      _observables(other._observables)
 {
@@ -119,7 +120,7 @@ void RooFuncWrapper::loadParamsAndData(std::string funcName, RooAbsArg const *he
    }
 }
 
-void RooFuncWrapper::declareAndDiffFunction(std::string funcName, std::string const &funcBody)
+void RooFuncWrapper::declareAndDiffFunction(std::string funcName, std::string const &funcBody, bool createGradient)
 {
    std::string gradName = funcName + "_grad_0";
    std::string requestName = funcName + "_req";
@@ -139,6 +140,9 @@ void RooFuncWrapper::declareAndDiffFunction(std::string funcName, std::string co
    }
    _func = reinterpret_cast<Func>(gInterpreter->ProcessLine((funcName + ";").c_str()));
 
+   if (!createGradient)
+      return;
+
    // Calculate gradient
    gInterpreter->ProcessLine("#include <Math/CladDerivator.h>");
    // disable clang-format for making the following code unreadable.

roofit/roofitcore/test/testRooFuncWrapper.cxx

@@ -109,7 +109,7 @@ TEST(RooFuncWrapper, GaussianNormalizedHardcoded)
                       "const double sig = params[2];"
                       "double out = std::exp(-0.5 * arg * arg / (sig * sig));"
                       "return 1. / (std::sqrt(TMath::TwoPi()) * sig) * out;";
-   RooFuncWrapper gaussFunc("myGauss1", "myGauss1", func, {x, mu, sigma}, {});
+   RooFuncWrapper gaussFunc("myGauss1", "myGauss1", func, {x, mu, sigma}, nullptr, nullptr, true);
 
    // Check if functions results are the same even after changing parameters.
    EXPECT_NEAR(gauss.getVal(normSet), gaussFunc.getVal(), 1e-8);
@@ -149,7 +149,7 @@ TEST(RooFuncWrapper, GaussianNormalized)
 
    RooArgSet normSet{x};
 
-   RooFuncWrapper gaussFunc("myGauss3", "myGauss3", gauss, normSet);
+   RooFuncWrapper gaussFunc("myGauss3", "myGauss3", gauss, normSet, nullptr, nullptr, true);
 
    RooArgSet paramsGauss;
    gauss.getParameters(nullptr, paramsGauss);
@@ -189,7 +189,7 @@ TEST(RooFuncWrapper, Exponential)
 
       RooArgSet normSet{x};
 
-      RooFuncWrapper expoFunc(name.c_str(), name.c_str(), expo, normSet);
+      RooFuncWrapper expoFunc(name.c_str(), name.c_str(), expo, normSet, nullptr, nullptr, true);
 
       RooArgSet params;
       expo.getParameters(nullptr, params);