Re: [PATCH V5 1/4] rs6000: build constant via li;rotldi

[Jiufu Guo <guojiufu@linux.ibm.com>]

Hi,

Gentle ping...

BR,
Jeff (Jiufu Guo)

Jiufu Guo <guojiufu@linux.ibm.com> writes:

> Hi,
>
> If a constant is possible to be rotated to/from a positive or negative
> value which "li" can generated, then "li;rotldi" can be used to build
> the constant.
>
> Compare with the previous version:
> https://gcc.gnu.org/pipermail/gcc-patches/2023-July/623528.html
> This patch just did minor changes to the comments according to previous
> review.
>
> 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_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'.
> +
> +   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
> @@ -0,1 +1,57 @@
> +/* { dg-do run } */
> +/* { dg-options "-O2 -save-temps" } */
> +/* { dg-require-effective-target has_arch_ppc64 } */
> +
> +/* Verify that two instructions are successfully used to build constants.
> +   One insn is li, another is rotate: rldicl.  */
> +
> +#define NOIPA __attribute__ ((noipa))
> +
> +struct fun
> +{
> +  long long (*f) (void);
> +  long long val;
> +};
> +
> +long long NOIPA
> +li_rotldi_1 (void)
> +{
> +  return 0x7531000000000LL;
> +}
> +
> +long long NOIPA
> +li_rotldi_2 (void)
> +{
> +  return 0x2100000000000064LL;
> +}
> +
> +long long NOIPA
> +li_rotldi_3 (void)
> +{
> +  return 0xffff8531ffffffffLL;
> +}
> +
> +long long NOIPA
> +li_rotldi_4 (void)
> +{
> +  return 0x21ffffffffffff94LL;
> +}
> +
> +struct fun arr[] = {
> +  {li_rotldi_1, 0x7531000000000LL},
> +  {li_rotldi_2, 0x2100000000000064LL},
> +  {li_rotldi_3, 0xffff8531ffffffffLL},
> +  {li_rotldi_4, 0x21ffffffffffff94LL},
> +};
> +
> +/* { dg-final { scan-assembler-times {\mrotldi\M} 4 } } */
> +
> +int
> +main ()
> +{
> +  for (int i = 0; i < sizeof (arr) / sizeof (arr[0]); i++)
> +    if ((*arr[i].f) () != arr[i].val)
> +      __builtin_abort ();
> +
> +  return 0;
> +}