icx does not vectorize code without pragma vector always

hansvz — Wed, 26 Mar 2025 12:40:01 GMT

I have a short code snippet (purely as an example of an issue I think I'm running into a lot with icx). We are trying to switch from icl to icx, but we''re experiencing a performance degradtion on our code base of around 30%.

Godbolt compiler explorer link: https://godbolt.org/z/GWEaGqj3o

As you can see, I have a very simple loop that fills an array. icl vectorizes it, icx does not, unless I change the pragma vector aligned to pragma vector always. The (measured) performance difference is a factor 4. But, vec-report says that vectorizing it does not help, so icx does not vectorize it without adding this pragma.

Am I missing something obvious here?

(I tried to add code snippets in this post, but unfortunately the forum keeps flagging it as spam).

topic icx does not vectorize code without pragma vector always in Intel® oneAPI DPC++/C++ Compiler

icx does not vectorize code without pragma vector always