------- Comment #23 from eyal at geomage dot com 2008-02-10 15:47 ------- (In reply to comment #22) > 1. It looks like vectorizer was enabled in both cases, since -O3 enables the > vectorizer by the default. You need to add -fno-tree-vectorize to disable it > explicitly. > 2. To get better results from vectorized version I would recommend to allocate > arrays at boundaries aligned to 16 byte and let to the compiler to know this. > You can do it by static allocation of arrays: > float pSum1[64000] __attribute__ ((__aligned__(16))); > float pSum[64000] __attribute__ ((__aligned__(16))); > float pVec1[64000] __attribute__ ((__aligned__(16))); > 3. It would be better if "itBegin" will start from 0 and be known at compile > time. This and [2] will allow to vectorizer to save realigning loads. > 4. For some strange reason the run time of this test can vary significantly > (up > to 50%) from run to run. So be sure to run it several times. > -- Victor.
Hi, Item 2 is problematic as the data can vary a lot and I cant use static arrays. Im also willing to pay a "reasonable" price for the alignment extra actions. Item 3: I cant make itBegin start from zero, since this is how the formula we're using works. Its calculated everytime and can vary in value. Item 4: I saw consistent results everytime I ran it. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35117
