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Date: Sun, 21 Jun 2015 11:26:55 +0200
From: Xavier Leroy <Xavier.Leroy@inria.fr>
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Subject: Re: [Caml-list] mips32 backend without floating point hardware

On 21/06/15 04:17, Nicolas Ojeda Bar wrote:
> I am trying to get the mips o32 backend (from 1.*, ~17 years ago!)
> working again on machines without *any* floating point hardware.
> [...]
> This works well for the
> OCaml side of things, but the C abi dictates that float args should be
> passed in even-odd pairs of int registers (i.e., either a0-a1 or
> a2-a3).  Unfortunately I lost the Int/Float distinction after
> overloading regs_for, so I can't enforce this constraint in
> Proc.loc_external_arguments.  Similarly it is not possible to 8-align
> extra floats in the stack since the type information is lost.
> 
> Any ideas/suggestions how to fit this situation to the existing
> backend infrastructure ?

My suggestion is just to forget about soft floating-point altogether.
The back-end hacks that were introduced 10 years ago to support soft
FP on ARM don't quite work in the general case, as you describe above.
In the meantime, hardware FP is now provided by all the processors
that are powerful enough to run OCaml code.  Why bother?

- Xavier Leroy