Hi Segher! Thanks a lot for your comments!
Segher Boessenkool <seg...@kernel.crashing.org> writes: > Hi guys, > > 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'. 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 > >> > + HOST_WIDE_INT orig_c = c; > > If you ever feel you need a variable to hold an "orig" value, that is a > good hint that you should restructure the code a bit, perhaps even > factor it. That often is overdue (like here), not caused by you, but > you could help solve it ;-) > > (This is what made this patch hard to review, btw). You are right. Thanks for point out this! > >> > gen_rtx_IOR (DImode, copy_rtx (temp), >> > GEN_INT (ud1))); >> > } >> > + else if ((ud4 == 0xffff && ud3 == 0xffff) >> > + && ((ud1 & 0x8000) || (ud1 == 0 && !(ud2 & 0x8000)))) >> > + { >> > + temp = !can_create_pseudo_p () ? dest : gen_reg_rtx (DImode); >> > + >> > + HOST_WIDE_INT imm = (ud1 & 0x8000) ? ((ud1 ^ 0x8000) - 0x8000) >> > + : ((ud2 << 16) - 0x80000000); > > We really should have some "hwi::sign_extend (ud1, 16)" helper function, > heh. Maybe there already is? Ah, "sext_hwi". Fixing that up > everywhere in this function is preapproved. Great, thanks! > >> > + else >> > + { >> > + emit_move_insn (temp, >> > + GEN_INT (((ud2 << 16) ^ 0x80000000) - 0x80000000)); >> > + if (ud1 != 0) >> > + emit_move_insn (temp, gen_rtx_IOR (DImode, temp, GEN_INT (ud1))); >> > + emit_move_insn (dest, >> > + gen_rtx_ZERO_EXTEND (DImode, >> > + gen_lowpart (SImode, temp))); >> > + } > > Why this? Please just write it in DImode, do not go via SImode? Thanks for catch this. Yes, gen_lowpart with DImode would be ok. > >> > --- /dev/null >> > +++ b/gcc/testsuite/gcc.target/powerpc/pr106708.h >> > @@ -0,0 +1,9 @@ >> > +/* Test constants which can be built by li/lis + oris/xoris */ >> > +void __attribute__ ((__noinline__, __noclone__)) foo (long long *arg) >> > +{ >> > + *arg++ = 0x98765432ULL; >> > + *arg++ = 0xffffffff7cdeab55ULL; >> > + *arg++ = 0xffffffff65430000ULL; >> > +} > > Use noipa please (it is shorter, simpler, and covers more :-) ) Thanks! > > Could you comment what exact instructions are expected? > li;xoris and li;xoris and lis;xoris I guess? It helps if you just tell > the reader here. Sure, thanks! > > The li;oris and li;xoris parts look good. > BR, Jeff (Jiufu) > > Segher