On Sat, May 9, 2009 at 10:42 PM, Richard Guenther <richard.guent...@gmail.com> wrote: > On Sat, May 9, 2009 at 10:07 PM, Albert Cohen <albert.co...@inria.fr> wrote: >> Sebastian Pop and I have been discussing the option of designing a new pass, >> based on vrp, to normalize integer types towards a canonical supertype >> typically a machine word, equivalent to signed long, or to truncate to a >> smaller-size word when it makes sense. This would be a very simple pass (on >> top of not-so-simple vrp), but arguably a quite regression-prone one as well >> (due to aliases/escape and common C standard violations). >> >> The pass could be parameterized with three different objectives, depending >> on where it is scheduled in the pass manager. >> >> (1) canonicalize to the supertype aggressively, to facilitate the >> application of further passes like autovect which require very precise >> understanding of the type conversions; >> (2) compress the types to increase vectorization factor and reduce register >> pressure (assuming the target supports sub-word register allocation with >> register aliases); >> (3) optimize the types to minimize the dynamic number of casts that result >> in actual ASM instructions. >> >> Graphite and the vectorizer would clearly benefit from such a pass, at least >> if it implemented objective (1). >> >> I wonder if some of this is already implemented somewhere, or if someone >> played with it in the past, or is interesting in contributing. >> >> Nothing is planned yet on our side, and temporary fixes exist in the short >> term (as far as Graphite and the vectorizer are concerned), but it would >> potentially be of great help. > > This is certainly one useful transformation based on value-range information. > The choice of a canonical type is of course at least target dependent.
This btw. can at least partly replace the SEE (or the missed ZEE) pass. > I suppose you want to do this on register variables only? Did you think about > promoting function arguments and returns as well as part of an IPA pass? > > I don't understand how register variable promotion/demotion will help graphite > though - I had the impression graphite can only work on memory. No? > > Thanks, > Richard. >
