This change adds two builtins for AMDGPU:
- `__builtin_amdgcn_processor_is`, which is similar in observable
behaviour with `__builtin_cpu_is`, except that it is never "evaluated"
at run time;
- `__builtin_amdgcn_is_invocable`, which is behaviourally similar with
`__has_builtin`, except that it is not a macro (i.e. not evaluated at
preprocessing time).
Neither of these are `constexpr`, even though when compiling for
concrete (i.e. `gfxXXX` / `gfxXXX-generic`) targets they get evaluated
in Clang, so they shouldn't tear the AST too badly / at all for
multi-pass compilation cases like HIP. They can only be used in specific
contexts (as args to control structures).
The motivation for adding these is two-fold:
- as a nice to have, it provides an AST-visible way to incorporate
architecture specific code, rather than having to rely on macros and the
preprocessor, which burn in the choice quite early;
- as a must have, it allows featureful AMDGCN flavoured SPIR-V to be
produced, where target specific capability is guarded and chosen or
discarded when finalising compilation for a concrete target; this is
built atop the Speciali\ation Constant concept which is described in the
SPIR-V specification under section [2.12
Specialization](https://registry.khronos.org/SPIR-V/specs/unified1/SPIRV.html#_specialization_2)
I've tried to keep the overall footprint of the change small. The
changes to Sema are a bit unpleasant, but there was a strong desire to
have Clang validate these, and to constrain their uses, and this was the
most compact solution I could come up with (suggestions welcome).
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Co-authored-by: Juan Manuel Martinez Caamaño <jmartinezcaamao@gmail.com>
Co-authored-by: Voicu <avoicu@amd.com>
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