From d9ba1754584287487353ca765c4bfdfc711612f1 Mon Sep 17 00:00:00 2001
From: Giulio Eulisse <10544+ktf@users.noreply.github.com>
Date: Wed, 14 Oct 2026 23:42:14 +0200
Subject: [PATCH] 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.
---
 .../include/ReconstructionDataFormats/GlobalTrackID.h         | 4 ++--
 GPU/GPUTracking/TPCClusterFinder/CfChargePos.h                | 3 +++
 GPU/Utils/GPUCommonBitSet.h                                   | 3 +++
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/DataFormats/Reconstruction/include/ReconstructionDataFormats/GlobalTrackID.h b/DataFormats/Reconstruction/include/ReconstructionDataFormats/GlobalTrackID.h
index 63515261e544b..722dc75edb93a 100644
--- a/DataFormats/Reconstruction/include/ReconstructionDataFormats/GlobalTrackID.h
+++ b/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];
diff --git a/GPU/GPUTracking/TPCClusterFinder/CfChargePos.h b/GPU/GPUTracking/TPCClusterFinder/CfChargePos.h
index 3f1265e6d0634..38d6c78d1bb6e 100644
--- a/GPU/GPUTracking/TPCClusterFinder/CfChargePos.h
+++ b/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) {}
 
diff --git a/GPU/Utils/GPUCommonBitSet.h b/GPU/Utils/GPUCommonBitSet.h
index e35587ab60c7b..8e2331a1155b9 100644
--- a/GPU/Utils/GPUCommonBitSet.h
+++ b/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; }