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Date: Tue, 28 Apr 2009 23:36:14 +0400
Message-ID: <90823c940904281236x61204451nac149ee15b5df73a@mail.gmail.com>
Subject: Ocamlopt code generator question
From: Dmitry Bely <dmitry.bely@gmail.com>
To: Caml List <caml-list@inria.fr>
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X-Spam: no; 0.00; ocamlopt:01 asmcomp:01 mlp:01 ofs:01 ofs:01 pointer:01 dmitry:01 dmitry:01 bely:01 bely:01 conventions:02 conventions:02 caml:02 caml:02 floats:02 

For amd64 we have in asmcomp/amd64/proc_nt.mlp:

(*  xmm0 - xmm15  100 - 115       xmm0 - xmm9: Caml function arguments
                                xmm0 - xmm3: C function arguments
                                xmm0: Caml and C function results
                                xmm6-xmm15 are preserved by C *)

let loc_arguments arg =
  calling_conventions 0 9 100 109 outgoing arg
let loc_parameters arg =
  let (loc, ofs) = calling_conventions 0 9 100 109 incoming arg in loc
let loc_results res =
  let (loc, ofs) = calling_conventions 0 0 100 100 not_supported res in loc

What these first_float=100 and last_float=109 for loc_arguments and
loc_parameters affect? My impression is that floats are always passed
boxed, so xmm registers are in fact never used to pass parameters. And
float values are returned as a pointer in eax, not a value in xmm0 as
loc_results would suggest.

- Dmitry Bely