Re: [PATCH 4/4] rs6000: build constant via li/lis;rldic

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

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On Wed, Jun 7, 2023 at 9:56 PM Jiufu Guo <guojiufu@linux.ibm.com> wrote:

> Hi,
>
> This patch checks if a constant is possible to be built by "li;rldic".
> We only need to take care of "negative li", other forms do not need to
> check.
> For example, "negative lis" is just a "negative li" with an additional
> shift.
>
> Bootstrap and regtest pass on ppc64{,le}.
> Is this ok for trunk?
>
> BR,
> Jeff (Jiufu)
>
> gcc/ChangeLog:
>
>         * config/rs6000/rs6000.cc (can_be_built_by_li_and_rldic): New
> function.
>         (rs6000_emit_set_long_const): Call can_be_built_by_li_and_rldic.
>

This is okay.

Do you have any measurement of how expensive it is to test all of these
additional methods to generate a constant?  How much does this affect the
compile time?

Thanks, David



>
> gcc/testsuite/ChangeLog:
>
>         * gcc.target/powerpc/const-build.c: Add more tests.
> ---
>  gcc/config/rs6000/rs6000.cc                   | 61 ++++++++++++++++++-
>  .../gcc.target/powerpc/const-build.c          | 28 +++++++++
>  2 files changed, 88 insertions(+), 1 deletion(-)
>
> diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
> index 2a3fa733b45..cd04b6b5c82 100644
> --- a/gcc/config/rs6000/rs6000.cc
> +++ b/gcc/config/rs6000/rs6000.cc
> @@ -10387,6 +10387,64 @@ can_be_built_by_li_lis_and_rldicr (HOST_WIDE_INT
> c, int *shift,
>    return false;
>  }
>
> +/* Check if value C can be built by 2 instructions: one is 'li', another
> is
> +   rldic.
> +
> +   If so, *SHIFT is set to the 'shift' operand of rldic; and *MASK is set
> +   to the mask value about the 'mb' operand of rldic; and return true.
> +   Return false otherwise.  */
> +
> +static bool
> +can_be_built_by_li_and_rldic (HOST_WIDE_INT c, int *shift, HOST_WIDE_INT
> *mask)
> +{
> +  /* There are 49 successive ones in the negative value of 'li'.  */
> +  int ones = 49;
> +
> +  /* 1..1xx1..1: negative value of li --> 0..01..1xx0..0:
> +     right bits are shifted as 0's, and left 1's(and x's) are cleaned.  */
> +  int tz = ctz_hwi (c);
> +  int lz = clz_hwi (c);
> +  int middle_ones = clz_hwi (~(c << lz));
> +  if (tz + lz + middle_ones >= ones)
> +    {
> +      *mask = ((1LL << (HOST_BITS_PER_WIDE_INT - tz - lz)) - 1LL) << tz;
> +      *shift = tz;
> +      return true;
> +    }
> +
> +  /* 1..1xx1..1 --> 1..1xx0..01..1: some 1's(following x's) are cleaned.
> */
> +  int leading_ones = clz_hwi (~c);
> +  int tailing_ones = ctz_hwi (~c);
> +  int middle_zeros = ctz_hwi (c >> tailing_ones);
> +  if (leading_ones + tailing_ones + middle_zeros >= ones)
> +    {
> +      *mask = ~(((1ULL << middle_zeros) - 1ULL) << tailing_ones);
> +      *shift = tailing_ones + middle_zeros;
> +      return true;
> +    }
> +
> +  /* xx1..1xx: --> xx0..01..1xx: some 1's(following x's) are cleaned. */
> +  /* Get the position for the first bit of successive 1.
> +     The 24th bit would be in successive 0 or 1.  */
> +  HOST_WIDE_INT low_mask = (1LL << 24) - 1LL;
> +  int pos_first_1 = ((c & (low_mask + 1)) == 0)
> +                     ? clz_hwi (c & low_mask)
> +                     : HOST_BITS_PER_WIDE_INT - ctz_hwi (~(c | low_mask));
> +  middle_ones = clz_hwi (~c << pos_first_1);
> +  middle_zeros = ctz_hwi (c >> (HOST_BITS_PER_WIDE_INT - pos_first_1));
> +  if (pos_first_1 < HOST_BITS_PER_WIDE_INT
> +      && middle_ones + middle_zeros < HOST_BITS_PER_WIDE_INT
> +      && middle_ones + middle_zeros >= ones)
> +    {
> +      *mask = ~(((1ULL << middle_zeros) - 1LL)
> +               << (HOST_BITS_PER_WIDE_INT - pos_first_1));
> +      *shift = HOST_BITS_PER_WIDE_INT - pos_first_1 + middle_zeros;
> +      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.  */
> @@ -10435,7 +10493,8 @@ rs6000_emit_set_long_const (rtx dest,
> HOST_WIDE_INT c)
>      }
>    else if (can_be_built_by_li_lis_and_rotldi (c, &shift, &mask)
>            || can_be_built_by_li_lis_and_rldicl (c, &shift, &mask)
> -          || can_be_built_by_li_lis_and_rldicr (c, &shift, &mask))
> +          || can_be_built_by_li_lis_and_rldicr (c, &shift, &mask)
> +          || can_be_built_by_li_and_rldic (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 8c209921d41..b503ee31c7c 100644
> --- a/gcc/testsuite/gcc.target/powerpc/const-build.c
> +++ b/gcc/testsuite/gcc.target/powerpc/const-build.c
> @@ -82,6 +82,29 @@ lis_rldicr_12 (void)
>    return 0x5310000ffffffff0LL;
>  }
>
> +long long NOIPA
> +li_rldic_13 (void)
> +{
> +  return 0x000f853100000000LL;
> +}
> +long long NOIPA
> +li_rldic_14 (void)
> +{
> +  return 0xffff853100ffffffLL;
> +}
> +
> +long long NOIPA
> +li_rldic_15 (void)
> +{
> +  return 0x800000ffffffff31LL;
> +}
> +
> +long long NOIPA
> +li_rldic_16 (void)
> +{
> +  return 0x800000000fffff31LL;
> +}
> +
>  struct fun arr[] = {
>    {li_rotldi_1, 0x7531000000000LL},
>    {li_rotldi_2, 0x2100000000000064LL},
> @@ -95,11 +118,16 @@ struct fun arr[] = {
>    {li_rldicr_10, 0xffff8531fff00000LL},
>    {li_rldicr_11, 0x21fffffffff00000LL},
>    {lis_rldicr_12, 0x5310000ffffffff0LL},
> +  {li_rldic_13, 0x000f853100000000LL},
> +  {li_rldic_14, 0xffff853100ffffffLL},
> +  {li_rldic_15, 0x800000ffffffff31LL},
> +  {li_rldic_16, 0x800000000fffff31LL}
>  };
>
>  /* { dg-final { scan-assembler-times {\mrotldi\M} 6 } } */
>  /* { dg-final { scan-assembler-times {\mrldicl\M} 3 } } */
>  /* { dg-final { scan-assembler-times {\mrldicr\M} 3 } } */
> +/* { dg-final { scan-assembler-times {\mrldic\M} 4 } } */
>
>  int
>  main ()
> --
> 2.39.1
>
>