Re: GNAT 4.8 atomic access to 64-bit objects

[Georg Bauhaus <rm.dash-bauhaus@futureapps.de>]

On 15.11.13 22:33, Dmitry A. Kazakov wrote:

> Try this:
>
> with Interfaces;
> with Ada.Unchecked_Conversion;
> with Ada.Text_IO;
>
> procedure Test is
>     type T is mod 2**64;
>     type Atomic_T is new Interfaces.IEEE_Float_64;
>    ...
> end Test;
>
> The code generated looks horrific.
>

Maybe according to
http://stackoverflow.com/questions/15843159/are-32-bit-software-builds-typically-64-bit-optimized
simply wanting  movq  is not "mode compatible"; however,
if there are MMX registers in the CPU you are targetting,
the following may be a valid way to get  movq  nevertheless,
albeit using a 64 bit signedinteger.
The program was translated in 32 bit GNU/Linux, using GNAT GPL 2012.
It uses compiler intrinsics in ways adapted from GNAT.SSE.

with Ada.Text_IO;
with GNAT.SSE;

procedure Atoms is
    use GNAT.SSE;

    type m64 is array (0 .. 0) of Integer64;
    for m64'Alignment use 8;
    pragma Machine_Attribute (m64, "vector_type");
    pragma Machine_Attribute (m64, "may_alias");

    function ia32_psllq (Left : m64; Right : m64) return m64;
    pragma Import (Intrinsic, ia32_psllq, "__builtin_ia32_psllq");

    X : Integer64;
    F : m64;
    for X'Address use F'Address;
begin
    X := 123;
    F := ia32_psllq (F, m64'(0 => 1));
    Ada.Text_IO.Put_Line (Integer64'Image (X));  --  246
end Atoms;