Re: [patch][ARM] Fix 16-bit -> 64-bit multiply and accumulate

[Richard Earnshaw <rearnsha at arm dot com>]

On Fri, 2011-01-28 at 15:13 +0000, Andrew Stubbs wrote:
> On 28/01/11 14:12, Richard Earnshaw wrote:
> > So what happens to a variation of your testcase:
> >
> > long long foolong (long long x, short *a, short *b)
> >     {
> >         return x + (long long)*a * (long long)*b;
> >     }
> >
> > With your patch?  This should generate identical code to your original
> > test-case.
> >
> 
> The patch has no effect on that testcase - it's broken in some other 
> way, I think, and the same with and without my patch:
> 
>          ldrsh   r3, [r3, #0]
>          ldrsh   r2, [r2, #0]
>          push    {r4, r5}
>          asrs    r4, r3, #31
>          asrs    r5, r2, #31
>          mul     r4, r2, r4
>          mla     r4, r3, r5, r4
>          umull   r2, r3, r2, r3
>          adds    r3, r4, r3
>          adds    r0, r0, r2
>          adc     r1, r1, r3
>          pop     {r4, r5}
>          bx      lr
> 
> Hmmm, that probably doesn't add anything useful to the discussion. :(
> 
> I'll add that one to the todo list ...
> 
> Andrew
> 

Ouch!  I though that used to work :-(

R.