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

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

Hi David,

David Edelsohn <dje.gcc@gmail.com> writes:
>  
> Hi, Jiufu
> 	* config/rs6000/rs6000.cc (can_be_rotated_to_possitive_li): New function.
> 	(can_be_rotated_to_negative_li): New function.
> 	(can_be_built_by_li_and_rotldi): New function.
> 	(rs6000_emit_set_long_const): Call can_be_built_by_li_and_rotldi.
> In English the word "positive" contains one "s", not two.  Please correct throughout the patches.
> Also a style issue, comments before a function should be followed by a
> blank line.

Sure, I will update accordingly, and check other patches.

>> +/* Check if C can be rotated to a possitive value which 'li' instruction
> positive
>> +   is able to load.  If so, set *ROT to the number by which C is rotated,
>> +   and return true.  Return false otherwise.  */
> Add a blank line here
>> +static bool
>> +can_be_rotated_to_possitive_li (HOST_WIDE_INT c, int *rot)
> positive
>> +{
>> +  /* 49 leading zeros and 15 lowbits on the possitive value
> low bits, positive

Thanks for your careful review! 

>> +     generated by 'li' instruction.  */
>> +  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.
>> +
>> +   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,
>> +				   HOST_WIDE_INT *mask)
>> +{
>> +  int n;
>> +  if (can_be_rotated_to_possitive_li (c, &n)
>> +      || can_be_rotated_to_negative_li (c, &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.  */
>> @@ -10246,15 +10285,14 @@ 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)))
>> @@ -10278,6 +10316,19 @@ 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));
>> +      if (mask != HOST_WIDE_INT_M1)
> How is mask != HOST_WIDE_INT_M1? The call to can_by_built_by_li_and_rotldi() set it
> to that value and it is not modified in the interim statements.

Oh, Thanks for catching this!
Actually this line is shared for these patches.
"if (mask != HOST_WIDE_INT_M1)" is useful with patch [3/4], and it
should be merged into that patch.

Thanks again for your review!


>> +	temp = gen_rtx_AND (DImode, temp, GEN_INT (mask));
>> +      emit_move_insn (dest, temp);
>> +    }
>>    else if (ud3 == 0 && ud4 == 0)
>>      {
>>        temp = !can_create_pseudo_p () ? dest : gen_reg_rtx (DImode);
> Thanks, David