Re: gfortran fp16

[Tobias Burnus <tobias@codesourcery.com>]

On 17.05.22 12:09, Thomas König wrote:
> be might complement to the QP support for POWER in gcc 12, and I have actually thought about doing. The library has its gotchas, though - I do not suppose we can count on fp16 support for trigonometrics and similar, for example,

I think that mostly depends on what the hardware supports and what
has been implemented in the target code.

For instance nvptx supports tanh and ex2 (ex2(a) := 2**a)) for .f16 –
and nvidia.md also contains, e.g. '(define_insn "exp2hf2"' which operates on "HF".

And there is also the following in gcc/builtins.def:

DEF_C99_BUILTIN        (BUILT_IN_ACOSHF, "acoshf", BT_FN_FLOAT_FLOAT, ATTR_MATHFN_FPROUNDING_ERRNO)
DEF_C99_BUILTIN        (BUILT_IN_ASINHF, "asinhf", BT_FN_FLOAT_FLOAT, ATTR_MATHFN_FPROUNDING)
DEF_C99_BUILTIN        (BUILT_IN_ATANHF, "atanhf", BT_FN_FLOAT_FLOAT, ATTR_MATHFN_FPROUNDING_ERRNO)
DEF_C99_C90RES_BUILTIN (BUILT_IN_COSHF, "coshf", BT_FN_FLOAT_FLOAT, ATTR_MATHFN_FPROUNDING_ERRNO)
DEF_C99_C90RES_BUILTIN (BUILT_IN_SINHF, "sinhf", BT_FN_FLOAT_FLOAT, ATTR_MATHFN_FPROUNDING_ERRNO)
DEF_C99_C90RES_BUILTIN (BUILT_IN_TANHF, "tanhf", BT_FN_FLOAT_FLOAT, ATTR_MATHFN_FPROUNDING)
DEF_C99_COMPL_BUILTIN        (BUILT_IN_CACOSHF, "cacoshf", BT_FN_COMPLEX_FLOAT_COMPLEX_FLOAT, ATTR_MATHFN_FPROUNDING)
DEF_C99_COMPL_BUILTIN        (BUILT_IN_CASINHF, "casinhf", BT_FN_COMPLEX_FLOAT_COMPLEX_FLOAT, ATTR_MATHFN_FPROUNDING)
DEF_C99_COMPL_BUILTIN        (BUILT_IN_CATANHF, "catanhf", BT_FN_COMPLEX_FLOAT_COMPLEX_FLOAT, ATTR_MATHFN_FPROUNDING)
DEF_C99_COMPL_BUILTIN        (BUILT_IN_CCOSHF, "ccoshf", BT_FN_COMPLEX_FLOAT_COMPLEX_FLOAT, ATTR_MATHFN_FPROUNDING)
DEF_C99_COMPL_BUILTIN        (BUILT_IN_CSINHF, "csinhf", BT_FN_COMPLEX_FLOAT_COMPLEX_FLOAT, ATTR_MATHFN_FPROUNDING)
DEF_C99_COMPL_BUILTIN        (BUILT_IN_CTANHF, "ctanhf", BT_FN_COMPLEX_FLOAT_COMPLEX_FLOAT, ATTR_MATHFN_FPROUNDING)

But as said: the basic support for HF-supporting target should be simple,
supporting all the library is more difficult. But the question is whether
full support is needed or not. For 'acoshf' - if it is not available but
used, it is mostly a user problem - which can be fixed by a suitable libm.
I assume that on systems where HF is relevant, libm can be compiled such
that it works.

And in the compiler, you can use '#ifdef HAVE_HFmode' to check whether it exists.

Tobias

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