Re: [PATCH] PowerPC: Map IEEE 128-bit long double built-in functions

[Segher Boessenkool <segher@kernel.crashing.org>]

Hi!

On Thu, Nov 19, 2020 at 06:58:14PM -0500, Michael Meissner wrote:
> 	* config/rs6000/rs6000.c (rs6000_mangle_decl_assembler_name): Add
> 	support for mapping built-in function names for long double
> 	built-in functions if long double is IEEE 128-bit.

Please write what it does, not "add support".  Say what names it maps
to, importantly.  You don't need to list all, but what you wrote is
100% contentless.

> diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
> index a5188553593..35e9c844e17 100644
> --- a/gcc/config/rs6000/rs6000.c
> +++ b/gcc/config/rs6000/rs6000.c
> @@ -27065,57 +27065,128 @@ rs6000_globalize_decl_name (FILE * stream, tree decl)
>     library before you can switch the real*16 type at compile time.
>  
>     We use the TARGET_MANGLE_DECL_ASSEMBLER_NAME hook to change this name.  We
> -   only do this if the default is that long double is IBM extended double, and
> -   the user asked for IEEE 128-bit.  */
> +   only do this transformation if the __float128 type is enabled.  This
> +   prevents us from doing the transformation on older 32-bit ports that might
> +   have enabled using IEEE 128-bit floating point as the default long double
> +   type.  */

I still don't understand why you want to support some hypothetical and
untested configuration.

> +  /* { dg-final { scan-assembler {\mbl __ynieee128} } }  */

This kind of thing does not portably work (the function names can have
various prefixes added).


I cannot understand this code, and it does seem far from obviously
correct.  But, okay for trunk if you handle all fallout (and I mean all,
not just "all you consider important").


Segher