Hi Segher, 在 11/28/22 10:18 PM, Segher Boessenkool 写道: > On Mon, Nov 28, 2022 at 11:37:34AM +0800, Jiufu Guo wrote: >> Segher Boessenkool <seg...@kernel.crashing.org> writes: >>> On Fri, Nov 25, 2022 at 04:11:49PM +0800, Kewen.Lin wrote: >>>> on 2022/10/26 19:40, Jiufu Guo wrote: >>>> for "li/lis + oris/xoris", I interpreted it into four combinations: >>>> >>>> li + oris, lis + oris, li + xoris, lis + xoris. >>>> >>>> not sure just me interpreting like that, but the actual combinations >>>> which this patch adopts are: >>>> >>>> li + oris, li + xoris, lis + xoris. >>>> >>>> It's a bit off, but not a big deal, up to you to reword it or not. :) >>> >>> The first two are obvious, but the last one is almost never a good idea, >>> there usually are better ways to do the same. I cannot even think of >>> any case where this is best? A lis;rl* is always prefered (it can >>> optimise better, be combined with other insns). >> I understant your point here. The first two: 'li' for lowest 16bits, >> 'oris/xoris' for next 16bits. >> >> While for 'lis + xoris', it may not obvious, because both 'lis' and >> 'xoris' operates on 17-31bits. >> 'lis + xoris' is for case "32(1) || 1(0) || 15(x) || 16(0)". xoris is >> used to clean bit31. This case seems hard to be supported by 'rlxx'. > > Please put that in a separate patch? First do a patch with just > lis;x?oris. They are unrelated and different in almost every way. > I just send out two patches, one for "lis; xoris" and one for "li; x?oris".
https://gcc.gnu.org/pipermail/gcc-patches/2022-December/607617.html https://gcc.gnu.org/pipermail/gcc-patches/2022-December/607618.html Maybe, do we prefer to separate into 3 patches for review easily :-)? Thanks for review! BR, Jeff (Jiufu) >> I hit to find this case when I analyze what kind of constants can be >> build by two instructions. Checked the posssible combinations: >> "addi/addis" + "neg/ori/../xoris/rldX/rlwX/../sradi/extswsli"(those >> instructions which accept one register and one immediate). >> >> I also drafted the patch to use "li/lis+rlxx" to build constant. >> https://gcc.gnu.org/pipermail/gcc-patches/2022-September/601276.html >> https://gcc.gnu.org/pipermail/gcc-patches/2022-September/601277.html > > Those seem to do many things in one patch as well :-( It is very hard > to review such things, it takes many hours each to do properly. > > > Segher
