Ping^2 [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 via Gcc-patches <gcc-patches@gcc.gnu.org> writes:

> 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;
>> +}