[ was: Re: [Patch][nvptx] return true in libc_has_function for
function_sincos ]

On 9/26/20 6:47 PM, Tobias Burnus wrote:
> Found when looking at PR97203 (but having no effect there).
> 
> The GCC ME optimizes with -O1 (or higher) the
>   a = sinf(x)
>   b = cosf(x)
> to __builtin_cexpi(x, &a, &b)
> (...i as in internal; like cexp(z) but with with __real__ z == 0)
> 
> 
> In expand_builtin_cexpi, that is handles as:
>   if (optab_handler (sincos_optab, mode) != CODE_FOR_nothing)
>     ...
>   else if (targetm.libc_has_function (function_sincos))
>     ...
>   else
>         fn = builtin_decl_explicit (BUILT_IN_CEXPF);
> 
> And the latter is done. As newlib's cexpf does not know that
> __real__ z == 0, it calculates 'r = expf (__real__ z)' before
> invoking sinf and cosf on __imag__ z.
> 
> Thus, it is much faster to call 'sincosf', which also exists
> in newlib.
> 
> Solution: Return true for targetm.libc_has_function (function_sincos).
> 
> 
> NOTE: With -funsafe-math-optimizations (-O0 or higher),
> sinf/cosf and sincosf invoke .sin.approx/.cos/.approx instead of
> doing a library call.

This version takes care to enable sincos and sincosf, but not sincosl.

Target hook changes OK for trunk?

Thanks,
- Tom