On 2023-03-26 02:18 Jeff Law<jeffreya...@gmail.com> wrote: > > > >On 3/23/23 20:45, juzhe.zh...@rivai.ai wrote: >> Sounds like you are looking at redundant extension problem in RISC-V port. >> This is the issue I want to fix but I don't find the time to do that. >> My first impression is that we need to fix redundant extension in "ree" >> PASS. >> I am not sure. >It's actually quite a bit more complicated. > >Some extension elimination can and probably should be happening in >gimple. In gimple you have access to type information as well as range >information. So you have the opportunity to do things like rewrite the >IL to use different types when it's safe to do so, or to use range >information to identify when an object is already properly extended and >thus eliminate the extension before we expand gimple into RTL. > >Once in RTL, you can use forward propagation to eliminate extensions, or >at least fold them into existing operations. combine can eliminate >extensions and it has the ability to track (for example) if the upper >bits are copies of the sign bit, if they're known zero, etc. combine is >also capable of recognizing that a load implicitly extends and using >that knowledge to eliminate extensions or to discover that a pair of >shifts are just zero or sign extending a value, etc etc. combine also >interacts with simplify-rtx which is used by other passes, so there's a >chance that work in simplify-rtx can eliminate extensions not just in >combine, but in other passes as well. > >REE is a post-register allocation pass and kind of the last chance to >eliminate extensions. > >So for any given redundant extension, the way to go (IMHO) is to walk >through the optimizer pipeline to see where it can potentially be >eliminated. In general, the earlier in the optimizer pipeline the >extension can be eliminated, the better. > >Jeff Hi Jeff，Do you think my patch modification is suitable?What else needs to be improved？ Thanks.
Feng Wang
