DetectorsBase: place shared constants in the constant address space

MSL requires every variable at program scope, class-scope statics included, to
name an address space. GPUglobalconstexpr() expands to constexpr everywhere
except Metal, so this is a no-op for host, CUDA, HIP, OpenCL and cling.

Author: ktf

Detectors/Base/include/DetectorsBase/MatCell.h

@@ -26,9 +26,9 @@ namespace base
 struct MatCell {
   // small struct to hold <X/X0> and <rho> of the voxel
 
-  static constexpr int NParams = 2; // number of material parameters described
-  float meanRho;                    ///< mean density, g/cm^3
-  float meanX2X0;                   ///< fraction of radiaton lenght
+  static GPUglobalconstexpr() int NParams = 2; // number of material parameters described
+  float meanRho;                               ///< mean density, g/cm^3
+  float meanX2X0;                              ///< fraction of radiaton lenght
 
   GPUd() MatCell() : meanRho(0.f), meanX2X0(0.f) {}
   GPUdDefault() MatCell(const MatCell& src) = default;
@@ -51,8 +51,8 @@ struct MatCell {
 struct MatBudget : MatCell {
 
   // small struct to hold <X/X0>, <rho> and length traversed by track in the voxel
-  static constexpr int NParams = 3; // number of material parameters described
-  float length;                     ///< length in material
+  static GPUglobalconstexpr() int NParams = 3; // number of material parameters described
+  float length;                                ///< length in material
 
   GPUd() MatBudget() : length(0.f) {}
   GPUdDefault() MatBudget(const MatBudget& src) = default;

Detectors/Base/include/DetectorsBase/MatLayerCylSet.h

@@ -145,12 +145,12 @@ class MatLayerCylSet : public o2::gpu::FlatObject
   static constexpr size_t getBufferAlignmentBytes() { return 8; }
 #endif // !GPUCA_GPUCODE
 
-  static constexpr float LayerRMax = 500;    // maximum value of R lookup (corresponds to last layer of MatLUT)
-  static constexpr float VoxelRDelta = 0.05; // voxel spacing for layer lookup; seems a natural choice - corresponding ~ to smallest spacing
-  static constexpr float InvVoxelRDelta = 1.f / VoxelRDelta;
-  static constexpr int NumVoxels = int(LayerRMax / VoxelRDelta);
-  static constexpr uint16_t VoxelAmbiguousBit = 0x8000u;
-  static constexpr uint16_t VoxelSegmentMask = 0x7fffu;
+  static GPUglobalconstexpr() float LayerRMax = 500;    // maximum value of R lookup (corresponds to last layer of MatLUT)
+  static GPUglobalconstexpr() float VoxelRDelta = 0.05; // voxel spacing for layer lookup; seems a natural choice - corresponding ~ to smallest spacing
+  static GPUglobalconstexpr() float InvVoxelRDelta = 1.f / VoxelRDelta;
+  static GPUglobalconstexpr() int NumVoxels = int(LayerRMax / VoxelRDelta);
+  static GPUglobalconstexpr() uint16_t VoxelAmbiguousBit = 0x8000u;
+  static GPUglobalconstexpr() uint16_t VoxelSegmentMask = 0x7fffu;
 
   uint16_t mLayerVoxelLU[NumVoxels];     //! first interval based on known radius, plus the ambiguity flag (static dimension for easy copy to GPU)
   bool mInitializedLayerVoxelLU = false; //! if the voxels have been initialized

Detectors/Base/include/DetectorsBase/Propagator.h

@@ -16,6 +16,8 @@
 #ifndef ALICEO2_BASE_PROPAGATOR_
 #define ALICEO2_BASE_PROPAGATOR_
 
+#include "GPUCommonDef.h"
+
 #include "GPUCommonRtypes.h"
 #include "CommonConstants/PhysicsConstants.h"
 #include "ReconstructionDataFormats/Track.h"
@@ -69,8 +71,8 @@ class PropagatorImpl
     USEMatCorrLUT
   }; // flag to use LUT for material queries (user must provide a pointer
 
-  static constexpr float MAX_SIN_PHI = 0.85f;
-  static constexpr float MAX_STEP = 2.0f;
+  static GPUglobalconstexpr() float MAX_SIN_PHI = 0.85f;
+  static GPUglobalconstexpr() float MAX_STEP = 2.0f;
 
   GPUd() bool PropagateToXBxByBz(TrackParCov_t& track, value_type x,
                                  value_type maxSnp = MAX_SIN_PHI, value_type maxStep = MAX_STEP, MatCorrType matCorr = MatCorrType::USEMatCorrLUT,
@@ -201,7 +203,7 @@ class PropagatorImpl
   PropagatorImpl(bool uninitialized = false);
   ~PropagatorImpl() = default;
 #endif
-  static constexpr value_type Epsilon = 0.00001; // precision of propagation to X
+  static GPUglobalconstexpr() value_type Epsilon = 0.00001; // precision of propagation to X
   template <typename T>
   GPUd() void getFieldXYZImpl(const math_utils::Point3D<T> xyz, T* bxyz) const;
   template <typename T>

Detectors/Base/include/DetectorsBase/Ray.h

@@ -42,9 +42,9 @@ class Ray
 
  public:
   using vecF3 = float[3];
-  static constexpr float MinDistToConsider = 1e-4; // treat as 0 lenght distance below this
-  static constexpr float InvalidT = -1e9;
-  static constexpr float Tiny = 1e-9;
+  static GPUglobalconstexpr() float MinDistToConsider = 1e-4; // treat as 0 lenght distance below this
+  static GPUglobalconstexpr() float InvalidT = -1e9;
+  static GPUglobalconstexpr() float Tiny = 1e-9;
 
   GPUd() Ray() : mP{0.f}, mD{0.f}, mDistXY2(0.f), mDistXY2i(0.f), mDistXYZ(0.f), mXDxPlusYDy(0.f), mXDxPlusYDyRed(0.f), mXDxPlusYDy2(0.f), mR02(0.f), mR12(0.f)
   {