BOOST_MATH_SYCL_ENABLED is inescapable

[will-saunders-ukaea]

The macros at [1] assume that if SYCL_LANGUAGE_VERSION is defined then the user wants to use boost math with SYCL. However this macro is defined by the SYCL compiler even when it is compiling host only code.

1. The user may only want to use boost::math on the host and never the device. For example consider test code which uses boost::math as an alternative implementation to test against.
2. The user may use a intermediate library on the host which transitively includes boost::math.

These macros also assume that SYCL_EXTERNAL is defined [2]. However SYCL_EXTERNAL is optionally defined by the SYCL implementation if it is supported [3].

These macros define BOOST_MATH_NO_EXCEPTIONS which in turn triggers this bug [4]? This might be fixed as of 1.89.0?

Please can boost::math SYCL support be opt-in or at least opt-out?

Many thanks,
Will

[1]

math/include/boost/math/tools/config.hpp

Line 705 in 5e088ff

#elif defined(SYCL_LANGUAGE_VERSION)

[2]

math/include/boost/math/tools/config.hpp

Line 707 in 5e088ff

# define BOOST_MATH_SYCL_ENABLED SYCL_EXTERNAL

[3] https://registry.khronos.org/SYCL/specs/sycl-2020/html/sycl-2020.html#_preprocessor_directives_and_macros
[4] #1285

[mborland]

Since SYCL itself has opt-in device support I made our device support opt-in as well in the linked PR

[will-saunders-ukaea]

Thanks - the linked PR seems to solve the issue.