[Libre-soc-bugs] [Bug 558] gcc SV intrinsics concept

bugzilla-daemon at libre-soc.org bugzilla-daemon at libre-soc.org
Mon Dec 28 22:00:27 GMT 2020


https://bugs.libre-soc.org/show_bug.cgi?id=558

--- Comment #8 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from comment #5)
> and the stunning thing is: there's not even any need to change the rest of
> the compiler (except to add the svp64 prefix).  the *standard scalar add* is
> inherently vectorised by virtue of the context.

I'm pretty sure it is waay more complex than that, since the compiler has to
accurately represent all code, and the easiest way to accurately represent new
operations (which is what all SV ops are) is by using intrinsics, since they
look just like opaque function calls to most the compiler, so it won't try to
optimize them in a way that isn't valid with SV.

> no intrinsic vector mul.
> 
> no intrinsic vector add
> 
> no intrinsic scalar-vector mul

I wasn't proposing having scalar-vector ops since those can be represented by
_sv_mul(__sv_splat(lhs, ...), rhs, ...) and almost trivially pattern-matched at
instruction selection time into the scalar-vector instructions.

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