Re: Omitted conversion float -> double in x86 back-end

[Roberto COSTA <roberto dot costa at st dot com>]

Hi Michael,
too late, I've filed the report a few minutes ago.
By the way, if I want to bypass the problem without paying any 
performance penalty, it is sufficient that I introduce a temporary 
variable in the C source.
As a matter of fact, this looks to work:

double foo(signed long long l)
{
    double d = (float)l;
    return d;
}

Cheers,
Roberto



Michael Matz wrote:
> Hi,
>
> On Tue, 21 Nov 2006, Richard Guenther wrote:
>
> > but then regstack comes along and
> >
> > (insn:TI 10 32 33 2 (set (reg:SF 8 st)
> >        (float:SF (mem/c/i:DI (plus:SI (reg/f:SI 6 bp)
> >                    (const_int 8 [0x8])) [3 l+0 S8 A32]))) 172
> > {*floatdisf2_i387} (nil)
> >    (nil))
> >
> > where the *floatdisf2_i387 pattern misses the truncation to SFmode.
> >
> > (you should file a bugzilla about this)
>
> No you don't need to.  This is the usual x87-does-everything-in-extended 
> problem, i.e. PR 323.  There is no way to truncate that extended precision 
> to float (or double for that matter) without explicitely storing to 
> memory.  If you want to take that performance hit use -ffloat-store, in 
> which case the correct code will be produced:
>
> foo:
>         pushl   %ebp
>         movl    %esp, %ebp
>         subl    $16, %esp
>         fildll  8(%ebp)
>         fstps   -4(%ebp)
>         flds    -4(%ebp)
>         fstpl   -16(%ebp)
>         fldl    -16(%ebp)
>         leave
>         ret
>
> Better of course if to use SSE math.
>
>
> Ciao,
> Michael.