Re: [Caml-list] Compiler bug?

[Anil Madhavapeddy <anil@recoil.org>]

On 8 Aug 2012, at 11:22, Jesper Louis Andersen <jesper.louis.andersen@gmail.com> wrote:

> On Wed, Aug 8, 2012 at 8:03 PM, Alain Frisch <alain@frisch.fr> wrote:
> 
>> I'm not sure, someone else would have to reply!  I guess that these
>> registers are supposed to be preserved by the callee in the x64 ABI (and
>> obviously, they don't hold pointers to OCaml values, so they don't have to
>> be tracked by the GC).
> 
> Also, the GC itself will not be using Floating Point code at all, so
> we can save a lot by not saving/restoring these values on the stack.
> It is akin to what the Linux kernel does: trap on the first FP
> instruction and only then do work to save/restore the FP context - but
> here we know a priori we never will access FP. By doing so we can cut
> the time to the GC call down - and reap the benefits by having a
> faster GC cycle.

The GC does use floating point code in places. See byterun/major_gc.c
and the caml_major_collection_slice() function.  Gabor Pali is hacking on
a FreeBSD kernel module port of the OCaml runtime [1] and disabled all the
FP use to run without tripping over the trap checks in kFreeBSD [2].

[1] https://github.com/pgj/mirage-kfreebsd
[2] https://github.com/pgj/mirage-kfreebsd/commit/4c1859b88d6da540e7246e493809ff6f38ea344e

-anil