GPU: let the constant-address-space constants be built on Metal

A constructor's implicit `this` is generic in MSL 4.1, and a generic pointer does
not reach the constant address space, so a class-type constant at program scope
could not be constructed at all: gpustd::bitset for the DetID and GlobalTrackID
masks, CfChargePos for INVALID_CHARGE_POS.

MSL lets a member function be qualified with the address space of its `this`, so
each of the two constructors gains a constant-qualified overload next to the
existing one; for bitset that sits next to the __constant copy constructor
OpenCL already needs for the same reason.

Reading those constants back needs nothing further, with one exception:
sTrackSources is derived with operator| from the constant sMasks and then
indexed by isTrackSource. Rather than give bitset constant-qualified accessors
as well, that pair is left out of device code on Metal exactly as it already is
on OpenCL; its only caller is on the host.

Author: ktf

DataFormats/Reconstruction/include/ReconstructionDataFormats/GlobalTrackID.h

@@ -165,7 +165,7 @@ GPUconstexpr() GlobalTrackID::mask_t sMasks[GlobalTrackID::NSources] = ///< dete
     GlobalTrackID::mask_t(math_utils::bit2Mask(GlobalTrackID::MCHMID)) // Temporary ordering
 };
 
-#ifndef __OPENCL__
+#if !defined(__OPENCL__) && !defined(__METAL__)
 GPUconstexpr() GlobalTrackID::mask_t sTrackSources =
   sMasks[GlobalTrackID::ITS] | sMasks[GlobalTrackID::TPC] | sMasks[GlobalTrackID::MFT] | sMasks[GlobalTrackID::MCH] | sMasks[GlobalTrackID::ITSTPC] | sMasks[GlobalTrackID::TPCTOF] |
   sMasks[GlobalTrackID::TPCTRD] | sMasks[GlobalTrackID::MFTMCH] | sMasks[GlobalTrackID::ITSTPCTRD] | sMasks[GlobalTrackID::ITSTPCTOF] | sMasks[GlobalTrackID::TPCTRDTOF] |
@@ -177,7 +177,7 @@ GPUconstexpr() GlobalTrackID::mask_t sTrackSources =
 GPUdi() constexpr GlobalTrackID::DetID::mask_t GlobalTrackID::getSourceDetectorsMask(int i) { return globaltrackid_internal::SourceDetectorsMasks[i]; }
 GPUdi() constexpr GlobalTrackID::mask_t GlobalTrackID::getSourceMask(int s) { return globaltrackid_internal::sMasks[s]; }
 
-#ifndef __OPENCL__
+#if !defined(__OPENCL__) && !defined(__METAL__)
 GPUdi() bool GlobalTrackID::isTrackSource(int s)
 {
   return globaltrackid_internal::sTrackSources[s];

GPU/GPUTracking/TPCClusterFinder/CfChargePos.h

@@ -34,6 +34,9 @@ struct CfChargePos {
     : gpad(tpcGlobalPadIdx(row, pad)), timePadded(t + GPUCF_PADDING_TIME)
   {
   }
+#ifdef __METAL__
+  constexpr GPUhdi() CfChargePos(tpccf::Row row, tpccf::Pad pad, tpccf::TPCFragmentTime t) constant : gpad(tpcGlobalPadIdx(row, pad)), timePadded(t + GPUCF_PADDING_TIME) {}
+#endif
 
   GPUdi() CfChargePos(const tpccf::GlobalPad& p, const tpccf::TPCFragmentTime& t) : gpad(p), timePadded(t) {}
 

GPU/Utils/GPUCommonBitSet.h

@@ -47,6 +47,9 @@ class bitset
   GPUdDefault() constexpr bitset(const __constant bitset&) = default;
 #endif // __OPENCL__
   GPUd() constexpr bitset(uint32_t vv) : v(vv) {};
+#ifdef __METAL__
+  GPUd() constexpr bitset(uint32_t vv) constant : v(vv) {};
+#endif
   static GPUglobalconstexpr() uint32_t full_set = ((1ul << N) - 1ul);
 
   GPUd() constexpr bool all() const { return (v & full_set) == full_set; }