On Tue, 2014-09-30 at 11:04 -0500, Segher Boessenkool wrote: > On Tue, Sep 30, 2014 at 10:24:23AM -0500, Bill Schmidt wrote: > > On Tue, 2014-09-30 at 09:50 -0500, Segher Boessenkool wrote: > > > On Mon, Sep 29, 2014 at 05:26:14PM -0500, Bill Schmidt wrote: > > > > The method used in this patch is to perform a byte-reversal of the > > > > result of the lvsl/lvsr. This is accomplished by loading the vector > > > > char constant {0,1,...,15}, which will appear in the register from left > > > > to right as {15,...,1,0}. A vperm instruction (which uses BE element > > > > ordering) is applied to the result of the lvsl/lvsr using the loaded > > > > constant as the permute control vector. > > > > > > It would be nice if you could arrange the generated sequence such that > > > for the common case where the vec_lvsl feeds a vperm it is results in > > > just lvsr;vnot machine instructions. Not so easy to do though :-( > > > > Yes -- as you note, that only works when feeding a vperm, which is what > > we expect but generally a lot of work to prove. > > I meant generating a sequence that just "falls out" as you want it after > optimisation. E.g. lvsr;vnot;vand(splat8(31));vperm can have the vand > absorbed by the vperm. But that splat is nasty when not optimised away :-(
Especially since splat8(31) requires vsub(splat8(15),splat8(-16))... To get something that is correct with and without feeding a vperm and actually performs well just ain't happening here... > > > Again, this is > > deprecated usage so it seems not worth spending the effort on this... > > There is that yes :-) > > > > i++ is the common style. > > > > Now that we're being compiled as C++, ++i is the common style there -- > > The GCC source code didn't magically change to say "++i" everywhere it > said "i++" before, when we started compiling it with ++C :-P > > > is there guidance about this for gcc style these days? > > codingconventions.html doesn't say. > > grep | wc in rs6000/ shows 317 vs. 86; so a lot of stuff has already > leaked in (and in gcc/*.c it is 6227 vs. 793). Some days I think the > world has gone insane :-( > > To me "++i" reads as "danger, pre-increment!" Old habits I suppose. > I'll shut up now. Heh. I have to go back and forth between C and C++ a lot these days and find it's best for my sanity to just stick with the preincrement form now... Thanks, Bill > > > Segher >