Use static constexpr for improved compiler optimization

dumux/freeflow/compositional/staggered/fluxvariables.hh

@@ -75,7 +75,7 @@ public:
 
         const auto diffusiveFluxes = MolecularDiffusionType::flux(problem, element, fvGeometry, elemVolVars, scvf);
 
-        auto referenceSystemFormulation = MolecularDiffusionType::referenceSystemFormulation();
+        static constexpr auto referenceSystemFormulation = MolecularDiffusionType::referenceSystemFormulation();
 
         for (int compIdx = 0; compIdx < numComponents; ++compIdx)
         {

dumux/porousmediumflow/3p3c/localresidual.hh

@@ -135,7 +135,7 @@ public:
     {
         FluxVariables fluxVars;
         fluxVars.init(problem, element, fvGeometry, elemVolVars, scvf, elemFluxVarsCache);
-        auto referenceSystemFormulation = FluxVariables::MolecularDiffusionType::referenceSystemFormulation();
+        static constexpr auto referenceSystemFormulation = FluxVariables::MolecularDiffusionType::referenceSystemFormulation();
 
         // get upwind weights into local scope
         NumEqVector flux(0.0);

dumux/porousmediumflow/3pwateroil/localresidual.hh

@@ -171,7 +171,7 @@ public:
         EnergyLocalResidual::heatConductionFlux(flux, fluxVars);
 
         // diffusive fluxes
-        auto referenceSystemFormulation = FluxVariables::MolecularDiffusionType::referenceSystemFormulation();
+        static constexpr auto referenceSystemFormulation = FluxVariables::MolecularDiffusionType::referenceSystemFormulation();
         const auto diffusionFluxesWPhase = fluxVars.molecularDiffusionFlux(wPhaseIdx);
         Scalar jNW = diffusionFluxesWPhase[nCompIdx];
         // check for the reference system and adapt units of the diffusive flux accordingly.

dumux/porousmediumflow/compositional/localresidual.hh

@@ -143,7 +143,7 @@ public:
     {
         FluxVariables fluxVars;
         fluxVars.init(problem, element, fvGeometry, elemVolVars, scvf, elemFluxVarsCache);
-        auto referenceSystemFormulation = FluxVariables::MolecularDiffusionType::referenceSystemFormulation();
+        static constexpr auto referenceSystemFormulation = FluxVariables::MolecularDiffusionType::referenceSystemFormulation();
         // get upwind weights into local scope
         NumEqVector flux(0.0);
 

dumux/porousmediumflow/tracer/localresidual.hh

@@ -126,7 +126,7 @@ public:
         NumEqVector flux(0.0);
         const auto diffusiveFluxes = fluxVars.molecularDiffusionFlux(phaseIdx);
 
-        auto referenceSystemFormulation = FluxVariables::MolecularDiffusionType::referenceSystemFormulation();
+        static constexpr auto referenceSystemFormulation = FluxVariables::MolecularDiffusionType::referenceSystemFormulation();
         // formulation with mole balances
         if (useMoles)
         {
@@ -248,7 +248,7 @@ public:
         const auto advDerivIJ = volFlux*rho(outsideVolVars)*outsideWeight;
 
         // diffusive term
-        const auto referenceSystemFormulation = FluxVariables::MolecularDiffusionType::referenceSystemFormulation();
+        static constexpr auto referenceSystemFormulation = FluxVariables::MolecularDiffusionType::referenceSystemFormulation();
         const auto& fluxCache = elemFluxVarsCache[scvf];
         const Scalar rhoInside = massOrMolarDensity(insideVolVars, referenceSystemFormulation, phaseIdx);
         const Scalar rhoOutside = massOrMolarDensity(outsideVolVars, referenceSystemFormulation, phaseIdx);
@@ -307,7 +307,7 @@ public:
         const auto advDerivIJ = volFlux*rho(outsideVolVars)*outsideWeight;
 
         // diffusive term
-        auto referenceSystemFormulation = FluxVariables::MolecularDiffusionType::referenceSystemFormulation();
+        static constexpr auto referenceSystemFormulation = FluxVariables::MolecularDiffusionType::referenceSystemFormulation();
         using DiffusionType = GetPropType<T, Properties::MolecularDiffusionType>;
         const auto ti = DiffusionType::calculateTransmissibilities(problem,
                                                                    element,