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

[Arnold Schwaighofer]

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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>