Re: [PATCH 2/4] rs6000: build constant via lis;rotldi

[David Edelsohn <dje.gcc@gmail.com>]

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On Wed, Jun 7, 2023 at 9:55 PM Jiufu Guo <guojiufu@linux.ibm.com> wrote:

> Hi,
>
> This patch checks if a constant is possible to be rotated to/from a
> negative
> value from "lis".  If so, we could use "lis;rotldi" to build it.
> The positive value of "lis" does not need to be analyzed.  Because if a
> constant can be rotated from the positive value of "lis", it also can be
> rotated from a positive value of "li".
>
> Bootstrap and regtest pass on ppc64{,le}.
> Is this ok for trunk?
>
> BR,
> Jeff (Jiufu)
>
> gcc/ChangeLog:
>
>         * config/rs6000/rs6000.cc (can_be_rotated_to_negative_lis): New
>         function.
>         (can_be_built_by_li_and_rotldi): Rename to ...
>         (can_be_built_by_li_lis_and_rotldi): ... this function.
>         (rs6000_emit_set_long_const): Call
> can_be_built_by_li_lis_and_rotldi.
>

This patch is okay.

Thanks, David


>
> gcc/testsuite/ChangeLog:
>
>         * gcc.target/powerpc/const-build.c: Add more tests.
> ---
>  gcc/config/rs6000/rs6000.cc                   | 42 ++++++++++++++++---
>  .../gcc.target/powerpc/const-build.c          | 16 ++++++-
>  2 files changed, 52 insertions(+), 6 deletions(-)
>
> diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
> index 1dd0072350a..03cd9d5e952 100644
> --- a/gcc/config/rs6000/rs6000.cc
> +++ b/gcc/config/rs6000/rs6000.cc
> @@ -10278,19 +10278,51 @@ can_be_rotated_to_negative_li (HOST_WIDE_INT c,
> int *rot)
>    return can_be_rotated_to_lowbits (~c, 15, rot);
>  }
>
> -/* Check if value C can be built by 2 instructions: one is 'li', another
> is
> -   rotldi.
> +/* Check if C can be rotated to a negative value which 'lis' instruction
> is
> +   able to load: 1..1xx0..0.  If so, set *ROT to the number by which C is
> +   rotated, and return true.  Return false otherwise.  */
> +
> +static bool
> +can_be_rotated_to_negative_lis (HOST_WIDE_INT c, int *rot)
> +{
> +  /* case a. 1..1xxx0..01..1: up to 15 x's, at least 16 0's.  */
> +  int leading_ones = clz_hwi (~c);
> +  int tailing_ones = ctz_hwi (~c);
> +  int middle_zeros = ctz_hwi (c >> tailing_ones);
> +  if (middle_zeros >= 16 && leading_ones + tailing_ones >= 33)
> +    {
> +      *rot = HOST_BITS_PER_WIDE_INT - tailing_ones;
> +      return true;
> +    }
> +
> +  /* case b. xx0..01..1xx: some of 15 x's (and some of 16 0's) are
> +     rotated over the highest bit.  */
> +  int pos_one = clz_hwi ((c << 16) >> 16);
> +  middle_zeros = ctz_hwi (c >> (HOST_BITS_PER_WIDE_INT - pos_one));
> +  int middle_ones = clz_hwi (~(c << pos_one));
> +  if (middle_zeros >= 16 && middle_ones >= 33)
> +    {
> +      *rot = pos_one;
> +      return true;
> +    }
> +
> +  return false;
> +}
> +
> +/* Check if value C can be built by 2 instructions: one is 'li or lis',
> +   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.  */
>
>  static bool
> -can_be_built_by_li_and_rotldi (HOST_WIDE_INT c, int *shift,
> +can_be_built_by_li_lis_and_rotldi (HOST_WIDE_INT c, int *shift,
>                                    HOST_WIDE_INT *mask)
>  {
>    int n;
>    if (can_be_rotated_to_positive_li (c, &n)
> -      || can_be_rotated_to_negative_li (c, &n))
> +      || can_be_rotated_to_negative_li (c, &n)
> +      || can_be_rotated_to_negative_lis (c, &n))
>      {
>        *mask = HOST_WIDE_INT_M1;
>        *shift = HOST_BITS_PER_WIDE_INT - n;
> @@ -10346,7 +10378,7 @@ 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))
> +  else if (can_be_built_by_li_lis_and_rotldi (c, &shift, &mask))
>      {
>        temp = !can_create_pseudo_p () ? dest : gen_reg_rtx (DImode);
>        unsigned HOST_WIDE_INT imm = (c | ~mask);
> diff --git a/gcc/testsuite/gcc.target/powerpc/const-build.c
> b/gcc/testsuite/gcc.target/powerpc/const-build.c
> index 70f095f6bf2..c38a1dd91f2 100644
> --- a/gcc/testsuite/gcc.target/powerpc/const-build.c
> +++ b/gcc/testsuite/gcc.target/powerpc/const-build.c
> @@ -34,14 +34,28 @@ li_rotldi_4 (void)
>    return 0x21ffffffffffff94LL;
>  }
>
> +long long NOIPA
> +lis_rotldi_5 (void)
> +{
> +  return 0xffff85310000ffffLL;
> +}
> +
> +long long NOIPA
> +lis_rotldi_6 (void)
> +{
> +  return 0x5310000ffffffff8LL;
> +}
> +
>  struct fun arr[] = {
>    {li_rotldi_1, 0x7531000000000LL},
>    {li_rotldi_2, 0x2100000000000064LL},
>    {li_rotldi_3, 0xffff8531ffffffffLL},
>    {li_rotldi_4, 0x21ffffffffffff94LL},
> +  {lis_rotldi_5, 0xffff85310000ffffLL},
> +  {lis_rotldi_6, 0x5310000ffffffff8LL},
>  };
>
> -/* { dg-final { scan-assembler-times {\mrotldi\M} 4 } } */
> +/* { dg-final { scan-assembler-times {\mrotldi\M} 6 } } */
>
>  int
>  main ()
> --
> 2.39.1
>
>