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

[Andrew Stubbs <ams at codesourcery dot com>]

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