- Why don't we use the normal reverse postorder (or postorder) approach of computing live ranges? Is that because we don't really need full global live ranges?
Yes. We don't need global live ranges. - Why can't we use existing code i.e. tree-ssa-live? I suspect I already know the answer but an explanation (in a comment) would still be useful. The existing code can't help I have tried many times. - Do we really need get_all_predecessors/get_all_successors? As they're only used for "defined before" and "used after", at first glance it looks like some kind of dominance info could help there but I didn't really check in detail. Yes. At the first time, I want to use dominance analysis but I am not sure whether we can use df_analyze () in COST model framwork. It worth trying. - Why don't we use bitmaps/sbitmaps like in vsetvl.cc and other related passes? I don't mind maps but just wonder if it's on purpose, for convenience or something else. I don't know how to use bitmap to substitue the current approach of using map. Besides, it might help to rename program_points_map (into program_points_per_bb or so). At first it looked quadratic to me but we're just iterating over the program points of a BB. Ok. juzhe.zh...@rivai.ai From: Robin Dapp Date: 2023-09-06 05:02 To: Juzhe-Zhong; gcc-patches CC: rdapp.gcc; kito.cheng; kito.cheng; jeffreyalaw Subject: Re: [PATCH V2] RISC-V: Support Dynamic LMUL Cost model Hi Juzhe, I think the general approach makes sense and it doesn't need to be perfect from the beginning as we can always iterate on it. Before continuing with a more detailed review (hopefully tomorrow) some high-level questions upfront. It would help to document some of these choices so it's easier to understand the rationale. - Why don't we use the normal reverse postorder (or postorder) approach of computing live ranges? Is that because we don't really need full global live ranges? - Why can't we use existing code i.e. tree-ssa-live? I suspect I already know the answer but an explanation (in a comment) would still be useful. - Do we really need get_all_predecessors/get_all_successors? As they're only used for "defined before" and "used after", at first glance it looks like some kind of dominance info could help there but I didn't really check in detail. - Why don't we use bitmaps/sbitmaps like in vsetvl.cc and other related passes? I don't mind maps but just wonder if it's on purpose, for convenience or something else. Besides, it might help to rename program_points_map (into program_points_per_bb or so). At first it looked quadratic to me but we're just iterating over the program points of a BB. Regards Robin
