llvm calling convention matters

[Geoffrey Mainland]

We support compiling some code with -fllvm and some not in the same
executable. Otherwise how could users of the Haskell Platform link their
-fllvm-compiled code with native-codegen-compiled libraries like base, etc.?

In other words, the LLVM and native back ends use the same calling
convention. With my SIMD work, they still use the same calling
conventions, but the native codegen can never generate code that uses
SIMD instructions.

Geoff

On 09/11/2013 10:03 PM, Johan Tibell wrote:
> OK. But that doesn't create a problem for the code we output with the
> LLVM backend, no? Or do we support compiling some code with -fllvm and
> some not in the same executable?
>
>
> On Wed, Sep 11, 2013 at 6:56 PM, Geoffrey Mainland
> <mainland at apeiron.net <mailto:mainland at apeiron.net>> wrote:
>
>     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
>     difference.
>
>     Geoff
>
>     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>
>     <mailto: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>
>     <mailto: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
>     >
>     >
>     >
>
>