[Review]: Fix Integer Division Expansion special case of divide by 1

[Michael Ilseman]

If you have an example but just need help automating it, I can help with that as well. You can use e.g. lli to help identify such an example.


> On Jul 7, 2015, at 1:32 PM, Michael Ilseman <milseman at apple.com> wrote:
> 
>> 
>> On Jul 6, 2015, at 4:43 PM, Aditya Nandakumar <aditya_nandakumar at apple.com <mailto:aditya_nandakumar at apple.com>> wrote:
>> 
>> The problem is the check is a special case for handling X/1 - even if the special case is not being used, the expansion into the loop should still produce a valid quotient. It would be hard to test before and after for correctness.
>> The problem with the out of tree target is likely in the codegen of the expansion into the loop - and changing the special case of divide by 1 only fixes that case.
> 
> 
> I must not understand correctly. It sounds like you are positing the following:
> 1) There is a logic flaw that this corrects.
> 2) There is no bit pattern for the inputs/output that demonstrates this flaw.
> 
> #1 sounds probable, but I don’t understand how #2 is possible.
> 
>>> On Jul 6, 2015, at 4:35 PM, Michael Ilseman <milseman at apple.com> wrote:
>>> 
>>> Then can you sanitize and commit such a test case?
>>> 
>>>> On Jul 6, 2015, at 4:26 PM, Aditya Nandakumar <aditya_nandakumar at apple.com> wrote:
>>>> 
>>>> I don’t have a test case before and after for in-tree target but it fixed test for out of tree target.
>>>> The logic is what I am pointing out is wrong - we need to check if CTLZ(divisor) == Num_bits - 1 rather than CTLZ(divisor) - CTLZ(dividend).
>>>>> On Jul 6, 2015, at 2:29 PM, Michael Ilseman <milseman at apple.com> wrote:
>>>>> 
>>>>> Do you have a test case that demonstrates the failure before-hand, and the fix after? 
>>>>> 
>>>>>> On Jul 2, 2015, at 12:26 PM, Aditya Nandakumar <aditya_nandakumar at apple.com> wrote:
>>>>>> 
>>>>>> <DiffIntUnsignedDivision.patch>
>>>>> 
>>>> 
>>> 
>> 
> 
> 
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