Re: [PATCH] PR target/66144, PowerPC improve vector compare

[Segher Boessenkool <segher at kernel dot crashing dot org>]

On Fri, Feb 03, 2017 at 04:25:00PM -0500, Michael Meissner wrote:
> +;; Return 1 if operand is either a vector constant of all 0 bits of a vector
> +;; constant of all 1 bits.
> +(define_predicate "vector_int_same_bit"
> +  (match_code "const_vector")
> +{
> +  if (GET_MODE_CLASS (mode) != MODE_VECTOR_INT)
> +    return 0;
> +
> +  else
> +    return op == CONST0_RTX (mode) || op == CONSTM1_RTX (mode);
> +})

This predicate is unused as far as I see?

> +  /* Optimize vec1 == vec2, to know the mask generates -1/0.  */
> +  if (GET_MODE_CLASS (dest_mode) == MODE_VECTOR_INT)
>      {
> -      tmp = op_true;
> -      op_true = op_false;
> -      op_false = tmp;
> +      if (op_true == constant_m1 && op_false == constant_0)
> +	{
> +	  emit_move_insn (dest, mask);
> +	  return 1;
> +	}
> +
> +      else if (op_true == constant_0 && op_false == constant_m1)
> +	{
> +	  emit_insn (gen_rtx_SET (dest, gen_rtx_NOT (dest_mode, mask)));
> +	  return 1;
> +	}
>      }

Do you need to test for dest_mode == mask_mode here, like below?

> +  if (op_true == constant_m1 && dest_mode == mask_mode)
> +    op_true = mask;
> +  else if (!REG_P (op_true) && !SUBREG_P (op_true))
> +    op_true = force_reg (dest_mode, op_true);
> +
> +  if (op_false == constant_0 && dest_mode == mask_mode)
> +    op_false = mask;
> +  else if (!REG_P (op_false) && !SUBREG_P (op_false))
> +    op_false = force_reg (dest_mode, op_false);

Another thing you could try is, if either op_true or op_false is 0
or -1, let the result be
	(mask & op_true) | (~mask & op_false)

and let the rest of the optimisers sort it out (it's a single vor/vand
or vorc/vandc, or a vnot, or nothing).  A later improvement perhaps.
Or does it already handle all cases now :-)

Okay for trunk with the unused predicate removed, and the dest_mode ==
mask_mode thing looked at.  Thanks!


Segher