[PATCH][Loop Vectorizer] Identify basic FP recurrences in LoopVectorizer

[Tyler Nowicki]

Hi Arnold,

Thanks for the LGTM. I’ve been discussing the approach with my team and we arrived at another possible approach that might overcome the need for the refactoring you commented on. I am pursing this now. Hopefully it won’t be too long before I have a similar patch to test this.

Tyler

> On Jul 7, 2015, at 12:37 PM, Arnold Schwaighofer <aschwaighofer at apple.com> wrote:
> 
> LGTM.
> 
>> On Jun 17, 2015, at 10:37 AM, Tyler Nowicki <tnowicki at apple.com> wrote:
>> 
>> Hi Arnold,
>> 
>> It might be possible to combine both methods. Soon I’ll be extending AddBasicRecurrenceVar() to identify other uses of a recurrence, such as a store. I’ll try to combine them after that.
>> 
>> This is better?
>> 
>>  // A value in the basic recurrence can be used:                               
>>  //  - By the recurrence:                                                      
>>  //      - Recurrence operation:                                               
>>  //        - One use of recurrence value (safe).                               
>>  //        - Multiple use of recurrence value (not safe).                      
>>  //      - PHI:                                                                
>>  //        - All uses of the PHI must be the recurrence (safe).                
>>  //        - Otherwise, not safe.                                              
>>  //  - By out-of-loop instructions (not safe).                                 
>>  //  - By non-recurrence instructions in the loop:                             
>>  //      - Multiple uses by reductions (safe).                                 
>>  //      - Otherwise, not safe.                                                
>>  //    This is either:                                                         
>>  //      * An instruction type other than PHI or the recurrence operation.     
>>  //      * A PHI in the header other than the initial PHI.
>> 
>> Thanks for the review!
>> 
>> Tyler
>> 
>>> +  // A value in the simple recurrence can be used:
>>> +  //  - By the recurrence:
>>> +  //      - Recurrence operation:
>>> +  //        - One use of recurrence value (safe).
>>> +  //        - Multiple use of recurrence value (not safe).
>>> +  //      - PHI:
>>> +  //        - All uses of the PHI must be the recurrence (safe).
>>> +  //        - Otherwise, not safe.
>>> +  //  - By any instructions outside of the loop (not safe).
>>> 
>>> Here.
>>> 
>>> +  //  - By an instruction that is not part of the recurrence:
>>> +  //      - Multiple uses by reductions (safe).
>>> +  //      - Multiple uses by stores (safe).
>>> +  //      - Otherwise, not safe.
>>> +  //    This is either:
>>> +  //      * An instruction type other than PHI or the reduction operation.
>>> +  //      * A PHI in the header other than the initial PHI.
>>> 
>>> 
>>> We should be able to refactor AddReductionVar and AddBasicRecurrenceVar into a common utility? They are largely identical.
>>> 
>>> Other than that this LGTM.
>>> 
>>> 
>>>> On Jun 13, 2015, at 6:59 PM, Tyler Nowicki <tnowicki at apple.com> wrote:
>>>> 
>>>> Hi,
>>>> 
>>>> I would appreciate a review of this patch. It builds off a couple of other patches that are also in review.
>>>> 
>>>> Thanks,
>>>> 
>>>> Tyler
>>>> 
>>>>> On Jun 3, 2015, at 6:29 PM, Tyler Nowicki <tnowicki at apple.com> wrote:
>>>>> 
>>>>> Hi,
>>>>> 
>>>>> This patch builds on the refactoring patches in "[PATCH][VECTORIZER] Refactor ReductionDescriptor to also support floating-point recurrences".
>>>>> 
>>>>> The patch identifies basic floating-point recurrences and emits diagnostic remarks when a recurrence is found. Tests in the patch look for the diagnostic messages to verify the recurrences were found.
>>>>> 
>>>>> Subsequent patches will make the loop vectorizer generate code for the basic recurrences. Basic recurrences are a lot like the basic reductions that are already identified and vectorized.
>>>>> 
>>>>> Thanks,
>>>>> 
>>>>> Tyler
>>>>> 
>>>>> <0003-Identify-Basic-FP-Recurrences-In-Loop-Vectorizer.patch>
>>>> 
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>> 
>