llvm calling convention matters

Geoffrey Mainland mainland at apeiron.net
Thu Sep 12 01:56:27 UTC 2013

We definitely have interop between the native codegen and the LLVM back
end now. Otherwise anyone who wanted to use the LLVM back end would have
to build GHC themselves. Interop means that users can install the
Haskell Platform and still use -fllvm when it makes a performance


On 09/11/2013 07:59 PM, Johan Tibell wrote:
> Do nothing different than you're doing for 7.8, we can sort it out
> later. Just put a comment on the primops saying they're LLVM-only. See
> e.g.
> https://github.com/ghc/ghc/blob/master/compiler/prelude/primops.txt.pp#L181
> for an example how to add docs to primops.
> I don't think we need interop between the native and the LLVM
> backends. We don't have that now do we (i.e. they use different
> calling conventions).
> On Wed, Sep 11, 2013 at 4:51 PM, Geoffrey Mainland
> <mainland at apeiron.net <mailto:mainland at apeiron.net>> wrote:
>     On 09/11/2013 07:44 PM, Johan Tibell wrote:
>     > On Wed, Sep 11, 2013 at 4:40 PM, Geoffrey Mainland
>     <mainland at apeiron.net <mailto:mainland at apeiron.net>> wrote:
>     > > Do you mean we need a reasonable emulation of the SIMD primops for
>     > > the native codegen?
>     >
>     > Yes. Reasonable in the sense that it computes the right result.
>     I can
>     > see that some code might still want to #ifdef (if the fallback isn't
>     > fast enough).
>     Two implications of this requirement:
>     1) There will not be SIMD in 7.8. I just don't have the time. In fact,
>     what SIMD support is there already will have to be removed if we
>     cannot
>     live with LLVM-only SIMD primops.
>     2) If we also require interop between the LLVM back-end and the native
>     codegen, then we cannot pass any SIMD vectors in registers---they all
>     must be passed on the stack.
>     My plan, as discussed with Simon PJ, is to not support SIMD primops at
>     all with the native codegen. If there is a strong feeling that
>     this *is
>     not* the way to go, the I need to know ASAP.
>     Geoff

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