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

[Michael Gottesman]

(Sorry there is a typo therein. When I say lowering is done for all 4 types for ResNo == 1 I meant for ResNo == 0 and ResNo == 1).

Michael

On May 18, 2013, at 5:26 PM, Michael Gottesman <mgottesman at apple.com> wrote:

> 
> On May 18, 2013, at 2:22 AM, Duncan Sands <duncan.sands at gmail.com> wrote:
> 
>> 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.
> 
> Hey Duncan,
> 
> In the updated patch are the changes that you requested (i.e. I am not just returning SDValue() in said patch). The lowering is done for all 4 types for ResNo == 1. I should have said something in the email enclosing the updated patch. My apologies for not being clearer.
> 
> Michael
> 
>> 
>>> 
>>> 
>>> 
>>> 
>>> 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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> 
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