[PATCH] Move transforms from InstCombine to InstSimplify

[David Majnemer]

Ping


On Fri, Jul 12, 2013 at 2:56 PM, David Majnemer <david.majnemer at gmail.com>wrote:

> On Thu, Jul 11, 2013 at 10:42 PM, Duncan Sands <duncan.sands at gmail.com>wrote:
>
>> Hi David,
>>
>>
>>          +      } else {
>>>         +        // 'shl CI2, x' produces [CI2, CI2 << (Width-1)]
>>>         +        Lower = CI2Value;
>>>         +        Upper = CI2Value.shl(Width - 1) + 1;
>>>
>>>
>>>     this one seems wrong to me.  Consider for example CI2 (in binary)
>>> equal to
>>>        10001000
>>>     Then Lower=10001000, Upper=00000001, but a left-shift by 1 of CI2 is
>>>     00010000 which is not in the range Lower .. Upper.
>>>
>>>
>>> Thanks, I've updated the patch so that we will set Lower to zero and
>>> Upper to
>>> CI2 << CLZ(CI2) which is conservative but, AFAIK, correct.
>>>
>>
>> are you sure?
>>
>> 10110000
>>
>> Lower = 0, Upper = 10110000, but shifting left by two gives 11000000
>> which is
>> out of the range.
>>
>
> Right again. I'm giving up on the general case, at least for now.
>
>
>>
>> Ciao, Duncan.
>>
>
>
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