------- Additional Comments From dberlin at gcc dot gnu dot org 2004-12-26 01:09 ------- Just to followup on irc discussions. Being able to coalesce this may require moving to a different out-of-ssa algorithm that is better at coalescing. All of the below take different approaches to the coalescing problem, however, they may provide some insight as to whether/how these two variables can be coalesced.
The briggs one (which is what morgan is based on, which is what the comments claim is used) is known not to coalesce a significant number of variables. A comparison of the two major algorithms for out-of-ssa (briggs and sreedhar's) can be found at http://www.is.titech.ac.jp/~sassa/papers-written/sassa-kohama-ito-ipsi04.pdf Sreedhar's removes roughly 80% more copies than brigg's algorithm. Note that the authors propose their own algorithm, even though it does significantly worse than sreedhars, so i don't consider it a serious contender here. Sreedhar's can be found at http://tinyurl.com/5axtl i have a copy of the paper if you have no access. In addition, yet another different approach to out-of-ssa coalescing was presented at cgo 2004. http://www.cgo.org/cgo2004/papers/21_14_rastello_f_revised.pdf I mention it because it supposedly can coalesce even more than sreedhar's algorithm is able to. I point these out only as references to hopefully be able coalesce these variables. I don't believe totally rewriting out-of-ssa would be apropos for 4.0 unless the new algorithm is significantly simpler, etc (maybe one of the above would be, i don't know). -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19038
