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Re: [PATCH (3/7)] Widening multiply-and-accumulate pattern matching
On Mon, Jul 11, 2011 at 6:55 PM, Andrew Stubbs <ams@codesourcery.com> wrote:
> On 07/07/11 10:58, Richard Guenther wrote:
>>
>> I think you should assume that series of widenings,
>> (int)(short)char_variable
>> are already combined. ?Thus I believe you only need to consider a single
>> conversion in valid_types_for_madd_p.
>
> Ok, here's my new patch.
>
> This version only allows one conversion between the multiply and addition,
> so assumes that VRP has eliminated any needless ones.
>
> That one conversion may either be a truncate, if the mode was too large for
> the meaningful data, or an extend, which must be of the right flavour.
>
> This means that this patch now has the same effect as the last patch, for
> all valid cases (following you VRP patch), but rejects the cases where the C
> language (unhelpfully) requires an intermediate temporary to be of the
> 'wrong' signedness.
>
> Hopefully the output will now be the same between both -O0 and -O2, and
> programmers will continue to have to be careful about casting unsigned
> variables whenever they expect purely unsigned math. :(
>
> Is this one ok?
Ok.
Thanks,
Richard.
> Andrew
>