Hi Segher,

Thanks for your review!

Segher Boessenkool <seg...@kernel.crashing.org> writes:

> 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.

Sure, Thanks for the advice!
>
>> 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.
Sorry, I will try to seperate them to smaller granularities!

BR,
Jeff (Jiufu)
>
>
> Segher

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