On Fri, Nov 4, 2016 at 12:08 PM, Dominik Vogt <v...@linux.vnet.ibm.com> wrote: > On Fri, Nov 04, 2016 at 09:47:26AM +0100, Richard Biener wrote: >> On Thu, Nov 3, 2016 at 4:03 PM, Dominik Vogt <v...@linux.vnet.ibm.com> wrote: >> > Is VRP the right pass to do this optimisation or should a later >> > pass rather attempt to eliminate the new use of b_5 instead? Uli >> > has brought up the idea a mini "sign extend elimination" pass that >> > checks if the result of a sign extend could be replaced by the >> > original quantity in all places, and if so, eliminate the ssa >> > name. (I guess that won't help with the above code because l is >> > used also as a function argument.) How could a sensible approach >> > to deal with the situation look like? >> >> We run into this kind of situation regularly and for general foldings >> in match.pd we settled with single_use () even though it is not perfect. >> Note the usual complaint is not extra extension instructions but >> the increase of register pressure. >> >> This is because it is hard to do better when you are doing local >> optimization. >> >> As for the question on whether VRP is the right pass to do this the >> answer is two-fold -- VRP has the most precise range information. >> But the folding itself should be moved to generic code and use >> get_range_info (). > > All right, is this a sensible approach then?
Yes. > 1. Using has_single_use as in the experimental patch is good > enough (provided further testing does not show serious > regressions). I'd approve that, yes. > 2. Rip the whole top level if-block from simplify_cond_using_ranges(). > 3. Translate that code to match.pd syntax. Might be some work but yes, that's also desired (you'd lose the ability to emit the warnings though). Richard. > > Ciao > > Dominik ^_^ ^_^ > > -- > > Dominik Vogt > IBM Germany >
