Hi!
Segher Boessenkool <seg...@kernel.crashing.org> writes: > Hi! > > On Fri, Jun 16, 2023 at 04:34:12PM +0800, Jiufu Guo wrote: >> +/* Check if value C can be built by 2 instructions: one is 'li', another is >> + rotldi. >> + >> + If so, *SHIFT is set to the shift operand of rotldi(rldicl), and *MASK >> + is set to -1, and return true. Return false otherwise. */ > > Don't say "is set to -1", the point of having this is so you say "is set > to the "li" value". Just like you describe what SHIFT is for. Yes, thanks! > >> +static bool >> +can_be_built_by_li_and_rotldi (HOST_WIDE_INT c, int *shift, >> + HOST_WIDE_INT *mask) >> +{ >> + int n; > > Put shis later, like: Thanks! > >> + /* Check if C can be rotated to a positive or negative value >> + which 'li' instruction is able to load. */ > int n; >> + if (can_be_rotated_to_lowbits (c, 15, &n) >> + || can_be_rotated_to_lowbits (~c, 15, &n)) >> + { >> + *mask = HOST_WIDE_INT_M1; >> + *shift = HOST_BITS_PER_WIDE_INT - n; >> + return true; >> + } > > It is tricky to see ~c will always work, since what is really done is -c > instead. Can you just use that here? Some explanation: A negative value of 'li' is: 0b11..11xxx there are 49 leading '1's, and the other 15 tailing bits can be 0 or 1. With the '~' operation, there are 49 '0's. After the value is rotated, there are still 49 '1's. (xxx may also be at head/tail.) For the rotated value, with the '~' operation, there are still 49 '0's. So, for a value, if there are 49 successive '1's (may cross head/tail). It should be able to rotate to low 15 bits after the '~' operation. It would not be enough if using the '-' operation, since '-x=~x+1' in the bit aspect. As the below case 'li_rotldi_3': 0xffff8531ffffffffLL (rotate left 0x8531 32bit). The '~c' is 0x7ace00000000, this can be rotated from 0x7ace. (~0x8531). But '-c' is 0x7ace00000001. this value is not good. > >> @@ -10266,15 +10291,14 @@ static void >> rs6000_emit_set_long_const (rtx dest, HOST_WIDE_INT c) >> { >> rtx temp; >> + int shift; >> + HOST_WIDE_INT mask; >> HOST_WIDE_INT ud1, ud2, ud3, ud4; >> >> ud1 = c & 0xffff; >> - c = c >> 16; >> - ud2 = c & 0xffff; >> - c = c >> 16; >> - ud3 = c & 0xffff; >> - c = c >> 16; >> - ud4 = c & 0xffff; >> + ud2 = (c >> 16) & 0xffff; >> + ud3 = (c >> 32) & 0xffff; >> + ud4 = (c >> 48) & 0xffff; >> >> if ((ud4 == 0xffff && ud3 == 0xffff && ud2 == 0xffff && (ud1 & 0x8000)) >> || (ud4 == 0 && ud3 == 0 && ud2 == 0 && ! (ud1 & 0x8000))) >> @@ -10305,6 +10329,17 @@ rs6000_emit_set_long_const (rtx dest, HOST_WIDE_INT >> c) >> emit_move_insn (dest, gen_rtx_XOR (DImode, temp, >> GEN_INT ((ud2 ^ 0xffff) << 16))); >> } >> + else if (can_be_built_by_li_and_rotldi (c, &shift, &mask)) >> + { >> + temp = !can_create_pseudo_p () ? dest : gen_reg_rtx (DImode); >> + unsigned HOST_WIDE_INT imm = (c | ~mask); >> + imm = (imm >> shift) | (imm << (HOST_BITS_PER_WIDE_INT - shift)); >> + >> + emit_move_insn (temp, GEN_INT (imm)); >> + if (shift != 0) >> + temp = gen_rtx_ROTATE (DImode, temp, GEN_INT (shift)); >> + emit_move_insn (dest, temp); >> + } > > If you would rewrite so it isn't such a run-on thing with "else if", > instead using early outs, or even some factoring, you could declare the > variable used only in a tiny scope in that tiny scope instead. Yes! Early returning is better for a lot of cases. I would like to have a refactor patch. > >> --- /dev/null >> +++ b/gcc/testsuite/gcc.target/powerpc/const-build.c >> @@ -0,0 +1,54 @@ >> +/* { dg-do run } */ >> +/* { dg-options "-O2 -save-temps" } */ >> +/* { dg-require-effective-target has_arch_ppc64 } */ > > Please put a tiny comment here saying what this test is *for*? The file > name is a bit of hint already, but you can indicate much more in one or > two lines :-) Oh, yes, thanks for point out this! > > With those adjustments, okay for trunk. Thanks! > > (If -c doesn't work, it needs more explanation). Sure, some words as above. BR, Jeff (Jiufu Guo) > > > Segher