Hi Jeff,
on 2023/7/4 10:18, Jiufu Guo via Gcc-patches wrote:
> Hi,
>
> If a constant is possible to be rotated to/from a positive or negative
> value from "li", then "li;rotldi" can be used to build the constant.
>
> Compare with the previous version:
> https://gcc.gnu.org/pipermail/gcc-patches/2023-June/621961.html
> This patch just did minor changes to the style and comments.
>
> Bootstrap and regtest pass on ppc64{,le}.
>
> Since the previous version is approved with conditions, this version
> explained the concern too. If no objection, I would like to apply
> this patch to trunk.
>
>
> BR,
> Jeff (Jiufu)
>
> gcc/ChangeLog:
>
> * config/rs6000/rs6000.cc (can_be_built_by_li_and_rotldi): New function.
> (rs6000_emit_set_long_const): Call can_be_built_by_li_and_rotldi.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.target/powerpc/const-build.c: New test.
> ---
> gcc/config/rs6000/rs6000.cc | 47 +++++++++++++--
> .../gcc.target/powerpc/const-build.c | 57 +++++++++++++++++++
> 2 files changed, 98 insertions(+), 6 deletions(-)
> create mode 100644 gcc/testsuite/gcc.target/powerpc/const-build.c
>
> diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
> index 42f49e4a56b..acc332acc05 100644
> --- a/gcc/config/rs6000/rs6000.cc
> +++ b/gcc/config/rs6000/rs6000.cc
> @@ -10258,6 +10258,31 @@ rs6000_emit_set_const (rtx dest, rtx source)
> return true;
> }
>
> +/* Check if value C can be built by 2 instructions: one is 'li', another is
> + rotldi.
Nit: different style, li is with "'" but rotldi isn't.
> +
> + If so, *SHIFT is set to the shift operand of rotldi(rldicl), and *MASK
> + is set to the mask operand of rotldi(rldicl), and return true.
> + Return false otherwise. */
> +
> +static bool
> +can_be_built_by_li_and_rotldi (HOST_WIDE_INT c, int *shift,
> + HOST_WIDE_INT *mask)
> +{
> + /* If C or ~C contains at least 49 successive zeros, then C can be rotated
> + to/from a positive or negative value that 'li' 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;
> + }
> +
> + return false;
> +}
> +
> /* Subroutine of rs6000_emit_set_const, handling PowerPC64 DImode.
> Output insns to set DEST equal to the constant C as a series of
> lis, ori and shl instructions. */
> @@ -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);
> + }
> else if (ud3 == 0 && ud4 == 0)
> {
> temp = !can_create_pseudo_p () ? dest : gen_reg_rtx (DImode);
> diff --git a/gcc/testsuite/gcc.target/powerpc/const-build.c
> b/gcc/testsuite/gcc.target/powerpc/const-build.c
> new file mode 100644
> index 00000000000..69b37e2bb53
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/powerpc/const-build.c
> @@ -0,0 +1,57 @@
> +/* { dg-do run } */
> +/* { dg-options "-O2 -save-temps" } */
> +/* { dg-require-effective-target has_arch_ppc64 } */
> +
> +/* Verify that two instructions are sucessfully used to build constants.
s/sucessfully/successfully/
> + One insn is li or lis, another is rotate: rldicl, rldicr or rldic. */
Nit: This patch is for insn li + insn rldicl only, you probably want to keep
consistent in the comments.
The others look good to me, thanks!
Segher had one question on "~c" before, I saw you had explained for it, it
makes sense to me, but in case he has more questions I'd defer the final
approval to him.
BR,
Kewen
