Re: 01/03: gnu: Add QD.

[Mark H Weaver <mhw@netris.org>]

Hi Eric,

Eric Bavier <ericbavier@centurylink.net> writes:

> On Sat, 03 Feb 2018 22:55:56 -0500
> Mark H Weaver <mhw@netris.org> wrote:
>
>> ericbavier@centurylink.net (Eric Bavier) writes:
>> > +     `(#:configure-flags `("--disable-enable_fma" ;weird :/  
>> 
>> "weird :/" is not a very useful comment.
>
> Sorry.  I thought it was obvious it was in reference to the
> "disable-enable" bit.

I thought that might be the case, but I was still curious why you were
disabling FMA support, and the comment didn't help.

>>  Can you change it to explain
>> why you added this flag?  It seems unfortunate to disable fused
>> multiply-add for this kind of library.
>
> The library does not support runtime ISA detection.  I thought FMAs are
> something we don't support in our baseline x86-64 builds?

Indeed.  I was surprised to learn that FMAs are only supported in very
recent Intel processors.  My Yeeloong with MIPS-based Loongson 2F
processor from 2008 includes support for FMA instructions, and I guessed
that Intel had them long before, but actually Intel didn't add them
until several years later.

       Mark