[PATCH] [Multiprecision Arithmetic Optimization] Teach SelectionDAG how to promote the integer carry result of {add, sub}{c, e} to a larger integer type.

[Duncan Sands]

Hi Michael,

On 17/05/13 23:33, Michael Gottesman wrote:
> Hows this look Duncan/Sean?

returning SDValue() in PromoteIntRes_ADDSUBC is not valid.  There is no default
method that can be fallen back to.  If you don't want to handle the ResNo != 1
case then you must assert/fail, not just return SDValue().

Ciao, Duncan.

>
>
>
>
> Michael
>
> On May 16, 2013, at 10:41 AM, Michael Gottesman <mgottesman at apple.com
> <mailto:mgottesman at apple.com>> wrote:
>
>> I am trying to be incremental and did not have a need for such lowering. On
>> the other hand if you want I can implement that in this patch. Just state your
>> preference = ).
>>
>> Michael
>>
>> On May 16, 2013, at 1:34 AM, Duncan Sands <duncan.sands at gmail.com
>> <mailto:duncan.sands at gmail.com>> wrote:
>>
>>> Hi Michael,
>>>
>>> On 15/05/13 19:37, Michael Gottesman wrote:
>>>> The attached patch teaches selection DAG how to promote the integer carry
>>>> result of an {add,sub}{c,e} node to a larger integer type. It is a part of a
>>>> larger set of patches that I will be committing over the next little bit to
>>>> enable the optimization of uaddo/usubo chains.
>>>>
>>>> Please Review,
>>>> Michael
>>>
>>> +SDValue DAGTypeLegalizer::PromoteIntRes_ADDSUBC(SDNode *N, unsigned ResNo) {
>>> +  if (ResNo == 1)
>>> +    return PromoteIntRes_Overflow(N);
>>> +  return SDValue();
>>> +}
>>> +
>>> +SDValue DAGTypeLegalizer::PromoteIntRes_ADDSUBE(SDNode *N, unsigned ResNo) {
>>> +  if (ResNo == 1)
>>> +    return PromoteIntRes_Overflow(N);
>>> +  return SDValue();
>>> +}
>>>
>>> why do you return SDValue() if ResNo != 1 ?  Shouldn't you either assert or
>>> promote the value?
>>>
>>> Ciao, Duncan.
>>>
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