Re: [PATCH v2 3/9] Introduce can_vector_compare_p function

[Richard Sandiford <richard dot sandiford at arm dot com>]

Ilya Leoshkevich <iii@linux.ibm.com> writes:
> @@ -3819,6 +3820,82 @@ can_compare_p (enum rtx_code code, machine_mode mode,
>    return 0;
>  }
>  
> +/* can_vector_compare_p presents fake rtx binary operations to the the back-end
> +   in order to determine its capabilities.  In order to avoid creating fake
> +   operations on each call, values from previous calls are cached in a global
> +   cached_binops hash_table.  It contains rtxes, which can be looked up using
> +   binop_keys.  */
> +
> +struct binop_key {
> +  enum rtx_code code;        /* Operation code.  */
> +  machine_mode value_mode;   /* Result mode.     */
> +  machine_mode cmp_op_mode;  /* Operand mode.    */
> +};
> +
> +struct binop_hasher : pointer_hash_mark<rtx>, ggc_cache_remove<rtx> {
> +  typedef rtx value_type;
> +  typedef binop_key compare_type;
> +
> +  static hashval_t
> +  hash (enum rtx_code code, machine_mode value_mode, machine_mode cmp_op_mode)
> +  {
> +    inchash::hash hstate (0);
> +    hstate.add_int (code);
> +    hstate.add_int (value_mode);
> +    hstate.add_int (cmp_op_mode);
> +    return hstate.end ();
> +  }
> +
> +  static hashval_t
> +  hash (const rtx &ref)
> +  {
> +    return hash (GET_CODE (ref), GET_MODE (ref), GET_MODE (XEXP (ref, 0)));
> +  }
> +
> +  static bool
> +  equal (const rtx &ref1, const binop_key &ref2)
> +  {
> +    return (GET_CODE (ref1) == ref2.code)
> +	   && (GET_MODE (ref1) == ref2.value_mode)
> +	   && (GET_MODE (XEXP (ref1, 0)) == ref2.cmp_op_mode);
> +  }
> +};
> +
> +static GTY ((cache)) hash_table<binop_hasher> *cached_binops;
> +
> +static rtx
> +get_cached_binop (enum rtx_code code, machine_mode value_mode,
> +		  machine_mode cmp_op_mode)
> +{
> +  if (!cached_binops)
> +    cached_binops = hash_table<binop_hasher>::create_ggc (1024);
> +  binop_key key = { code, value_mode, cmp_op_mode };
> +  hashval_t hash = binop_hasher::hash (code, value_mode, cmp_op_mode);
> +  rtx *slot = cached_binops->find_slot_with_hash (key, hash, INSERT);
> +  if (!*slot)
> +    *slot = gen_rtx_fmt_ee (code, value_mode, gen_reg_rtx (cmp_op_mode),
> +			    gen_reg_rtx (cmp_op_mode));
> +  return *slot;
> +}

Sorry, I didn't mean anything this complicated.  I just meant that
we should have a single cached rtx that we can change via PUT_CODE and
PUT_MODE_RAW for each new query, rather than allocating a new rtx each
time.

Something like:

static GTY ((cache)) rtx cached_binop;

rtx
get_cached_binop (machine_mode mode, rtx_code code, machine_mode op_mode)
{
  if (cached_binop)
    {
      PUT_CODE (cached_binop, code);
      PUT_MODE_RAW (cached_binop, mode);
      PUT_MODE_RAW (XEXP (cached_binop, 0), op_mode);
      PUT_MODE_RAW (XEXP (cached_binop, 1), op_mode);
    }
  else
    {
      rtx reg1 = gen_raw_REG (op_mode, LAST_VIRTUAL_REGISTER + 1);
      rtx reg2 = gen_raw_REG (op_mode, LAST_VIRTUAL_REGISTER + 2);
      cached_binop = gen_rtx_fmt_ee (code, mode, reg1, reg2);
    }
  return cached_binop;
}

Thanks,
Richard