Alex Rivera | Logout

Does rewriting memcpy/memcmp/... with SIMD instructions make sense?

Asked 2011-03-16T05:21:57.310
17

Does rewriting memcpy/memcmp/... with SIMD instructions make sense in a large scale software?

If so, why doesn't GCC generate SIMD instructions for these library functions by default?

Also, are there any other functions can be possibly improved by SIMD?

performance sse simd
Edit
Report

1 Answer

9

Yes, these functions are much faster with SSE instructions. It would be nice if your runtime library/compiler instrinsics would include optimized versions, but that doesn't seem to be pervasive.

I have a custom SIMD memchr which is a hell-of-a-lot faster than the library version. Especially when I'm finding the first of 2 or 3 characters (example, I want to know if there's an equation in this line of text, I search for the first of =, \n, \r).

On the other hand, the library functions are well tested, so it's only worth writing your own if you call them a lot and a profiler shows they're a significant fraction of your CPU time.

answered 2011-03-16T05:31:12.910

Your Answer