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GPU: let the constant-address-space constants be built on Metal - #15963
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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.
davidrohr
approved these changes
Oct 14, 2026
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A constructor's implicit
thisis generic in MSL 4.1, and a generic pointer doesnot 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, soeach 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.