LLVM calling convention for AVX2 and AVX512 registers

[Edward Kmett]

Ugh. I apparently had a misunderstanding about how that was compiled.

-Edward

On Wed, Mar 15, 2017 at 5:14 PM, Ben Gamari <ben at smart-cactus.org> wrote:

> Edward Kmett <ekmett at gmail.com> writes:
>
> > Currently if you try to use a DoubleX4# and don't have AVX2 turned on, it
> > deliberately crashes out during code generation, no?
>
> I very well be missing something, but I don't believe this is true. This
> program compiles just fine with merely -fllvm -msse,
>
>     {-# LANGUAGE MagicHash #-}
>     {-# LANGUAGE UnboxedTuples #-}
>     module Hi where
>     import GHC.Prim
>     import GHC.Float
>
>     addIt :: DoubleX4# -> DoubleX4# -> DoubleX4#
>     addIt x y = plusDoubleX4# x y
>     {-# NOINLINE addIt #-}
>
> It produces the following assembler,,
>
>     movupd 0x10(%rbp),%xmm0
>     movupd 0x0(%rbp),%xmm1
>     movupd 0x30(%rbp),%xmm2
>     movupd 0x20(%rbp),%xmm3
>     addpd  %xmm1,%xmm3
>     addpd  %xmm0,%xmm2
>     movupd %xmm2,0x30(%rbp)
>     movupd %xmm3,0x20(%rbp)
>     mov    0x40(%rbp),%rax
>     lea    0x20(%rbp),%rbp
>     jmpq   *%rax
>
> The reason for this is that the LLVM code generator just blindly
> translates DoubleX4# to LLVM's <4 x double> type. The LLVM code
> generator then does whatever it can to produce the code we ask of it,
> even if the target doesn't have support for this vector variety.
>
> Cheers,
>
> - Ben
>
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