On Mar 13, 2012, at 6:01 PM, Sandeep Patel wrote: > 2012/3/13 Chris Lattner <[email protected]>: >> >> On Mar 13, 2012, at 1:21 PM, Rafael Espíndola wrote: >> >>>> the language ref currently says that it is undefined what gets stored in >>>> the >>>> other 7 bits when you write an i1. That was just to give freedom to be >>>> efficient, but should be changed to say "target dependent" or something >>>> like >>>> that if you want to go this way. >>> >>> Good point. I noticed the store had to be i1 for the i1 load to be >>> legal, but I missed this one. >> >> I really don't like "store of i1" having target-dependent semantics. If the >> real issue here is that we have no way to represent a "byte load that is >> known to be all ones at the top part" then we should add support for that >> directly IMO. >> >> Doing this should be relatively straightforward: just add a per-instruction >> metadata that indicates the number of leading zero bits that >> ComputeMaskedBits and friends can use. The hard part is designing something >> that is suitably general to capture other interesting properties. > > Just thinking out loud here -- > > Isn't this what metadata is for? Shouldn't we encode known value-range > limits as metadata and just attach it in the proper places? That might > lead nicely to future value-range optimization work.
Yep, lets discuss it in PR12251 -Chris _______________________________________________ cfe-commits mailing list [email protected] http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
