Scheduling complete loop unrolling early and unconditional?

[Devang Patel]

On Dec 22, 2004, at 10:19 AM, Richard Guenther wrote:

> Dorit Naishlos wrote:
>
>> just a comment -
>> for better or for worse, scheduling complete-unrolling early would 
>> take
>> away opportunities from autovectorization (at least as long as we're
>> looking for vectorization opportunities only across loop iterations 
>> and not
>> in straight-line code). Indeed if a loop gets completely unrolled 
>> then in
>> many cases it may be  too short to gain much if anything from
>> vectorization, but ideally the vectorizer would decide what's worth 
>> while
>> to vectorize and what not before such opportunities are eliminated (of
>> course we do not have such a cost model yet).
>
> Yes, of course.  But there is also a huge amount of manually unrolled
> code around like autogenerated stuff, but I also do manual unrolling
> sometimes.  So the best thing would be if the autovectorizer recognizes
> such straight-line "loop" code and other optimizations like SRA
> recognize constant-small-times running loops.

Yes, it is also in our list but there are few items ahead (e.g. mixed 
data
types, cost model, reduction transformation, breaking dependence cycles
etc...)

http://gcc.gnu.org/projects/tree-ssa/vectorization.html

-
Devang