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Re: [PATCH, RFC, rs6000] Add overloaded built-in function support to altivec.h, and re-implement vec_add


> 
> On Oct 31, 2016, at 5:28 PM, Bill Schmidt <wschmidt@linux.vnet.ibm.com> wrote:
> 
>   The other way would be to require a specific option on the command line
>   to use the new dispatch mechanism.  When the option is present, we would
>   predefine a macro such as __PPC_FAST_VECTOR__, which would then gate the
>   usage in altivec.h and overload.h.  Use of #pragma GCC target to change
>   the availability of Altivec, VMX, P8-vector, etc. would also be disallowed
>   when the option is present.  This has the advantage of always generating
>   correct code, at the cost of requiring a special option before anyone
>   can leverage the benefits of early vector expansion.  That's unfortunate,
>   but I suspect it's the best we can do.

Though I suppose we could require the option to turn off the new dispatch
mechanism, and document the change in gcc7/changes.html.  A little irritating
for people already using the pragma support, but I really expect this wouldn't affect
many people at all.

-- Bill

Bill Schmidt, Ph.D.
GCC for Linux on Power
Linux on Power Toolchain
IBM Linux Technology Center
wschmidt@linux.vnet.ibm.com


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