Hi Archie! The C2 compiler can use automatic vectorization [1] to speed up such operations. You can watch my explanation of the concept in some of my recent presentations, e.g, [2]
Best, Per YouTube<https://youtu.be/rXv2-lN5Xgk?t=1518> Share your videos with friends, family, and the world youtu.be Automatic vectorization - Wikipedia<https://en.wikipedia.org/wiki/Automatic_vectorization> Automatic vectorization, in parallel computing, is a special case of automatic parallelization, where a computer program is converted from a scalar implementation, which processes a single pair of operands at a time, to a vector implementation, which processes one operation on multiple pairs of operands at once. For example, modern conventional computers, including specialized supercomputers ... en.wikipedia.org [1] https://en.wikipedia.org/wiki/Automatic_vectorization [2] https://youtu.be/rXv2-lN5Xgk?t=1518 ________________________________ From: core-libs-dev <core-libs-dev-r...@openjdk.org> on behalf of Archie Cobbs <archie.co...@gmail.com> Sent: Thursday, May 22, 2025 10:58 PM To: John R Rose <jr...@openjdk.org> Cc: core-libs-dev@openjdk.org <core-libs-dev@openjdk.org> Subject: Re: RFR: 8357531: The `SegmentBulkOperations::fill` method can be improved using overlaps [v5] On Thu, May 22, 2025 at 3:31 PM John R Rose <jr...@openjdk.org<mailto:jr...@openjdk.org>> wrote: > Update benchmark to reflect new fill method Related discussion at the hardware level: https://github.com/openjdk/jdk/pull/25147#issuecomment-2902463076 This discussion spurred me to ask a dumb question. Apologies in advance, just trying to learn here... If I do this: import java.util.Arrays; public class ArrayFiller { public static void main(String[] args) { while (true) { final byte[] array = new byte[1000000]; Arrays.fill(array, (byte)0x42); } } } Will C2 compile Arrays.fill()<https://github.com/openjdk/jdk/blob/139a05d05959a84541a29dfae6151f92ce579ae6/src/java.base/share/classes/java/util/Arrays.java#L3275-L3308> into something that is more efficient than a byte-at-a-time loop like what appears in the source code? Thanks, -Archie -- Archie L. Cobbs
