A new WG21 paper is available. A copy is linked below, and the paper will also appear in the next normal WG21 mailing. If you are not a committee member, please use the comments section below or the std-proposals forum for public discussion.

Document number: N3561

Date: 2013-03-15

Semantics of Vector Loops

by Robert Geva, Clark Nelson

Excerpt:

In the SG1 conference call on Feb 5 2013, I presented the topic of a critical section in a vector loop. The discussion on the narrow topic itself resulted in the consensus that a critical section in a vector loops is undefined behavior. However, the discussion also led to broader interest in the semantics of a vector loop, which I was asked to present. This paper describes the semantics we propose. Note that this paper is meant as a continuation of earlier papers on vector loops, and is probably not self-contained. It does not repeat the syntax and language rules portions of the proposal.

As was stated in earlier meetings, this proposal is an attempt to codify existing practice in vector programming. While in a narrow sense, there are no existing practices of vector programming within standard C++, vector programming is broadly used in ad hoc ways. The expectations of programmers are well understood. The proposal here is not to invent new programming models. Instead, it is an attempt to codify the existing expectations of existing practitioners using C++ methodology.