[1/4] Missed opportunity to use [SU]ABD

  From: oluade01 <oluwatamilore.adebayo@arm.com>

This adds a recognition pattern for the non-widening
absolute difference (ABD).

gcc/ChangeLog:

	* doc/md.texi (sabd, uabd): Document them.
	* internal-fn.def (ABD): Use new optab.
	* optabs.def (sabd_optab, uabd_optab): New optabs,
	* tree-vect-patterns.cc (vect_recog_absolute_difference):
	Recognize the following idiom abs (a - b).
	(vect_recog_sad_pattern): Refactor to use
	vect_recog_absolute_difference.
	(vect_recog_abd_pattern): Use patterns found by
	vect_recog_absolute_difference to build a new ABD
	internal call.
---
 gcc/doc/md.texi           |  10 ++
 gcc/internal-fn.def       |   3 +
 gcc/optabs.def            |   2 +
 gcc/tree-vect-patterns.cc | 255 +++++++++++++++++++++++++++++++++-----
 4 files changed, 239 insertions(+), 31 deletions(-)
  

Thanks for the update.  Some of these comments would have applied
to the first version, so sorry for not catching them first time.

<Oluwatamilore.Adebayo@arm.com> writes:
> From: oluade01 <oluwatamilore.adebayo@arm.com>
>
> This adds a recognition pattern for the non-widening
> absolute difference (ABD).
>
> gcc/ChangeLog:
>
> 	* doc/md.texi (sabd, uabd): Document them.
> 	* internal-fn.def (ABD): Use new optab.
> 	* optabs.def (sabd_optab, uabd_optab): New optabs,
> 	* tree-vect-patterns.cc (vect_recog_absolute_difference):
> 	Recognize the following idiom abs (a - b).
> 	(vect_recog_sad_pattern): Refactor to use
> 	vect_recog_absolute_difference.
> 	(vect_recog_abd_pattern): Use patterns found by
> 	vect_recog_absolute_difference to build a new ABD
> 	internal call.
> ---
>  gcc/doc/md.texi           |  10 ++
>  gcc/internal-fn.def       |   3 +
>  gcc/optabs.def            |   2 +
>  gcc/tree-vect-patterns.cc | 255 +++++++++++++++++++++++++++++++++-----
>  4 files changed, 239 insertions(+), 31 deletions(-)
>
> diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi
> index 07bf8bdebffb2e523f25a41f2b57e43c0276b745..3e65584d7efcd301f2c96a40edd82d30b84462b8 100644
> --- a/gcc/doc/md.texi
> +++ b/gcc/doc/md.texi
> @@ -5778,6 +5778,16 @@ Other shift and rotate instructions, analogous to the
>  Vector shift and rotate instructions that take vectors as operand 2
>  instead of a scalar type.
>  
> +@cindex @code{uabd@var{m}} instruction pattern
> +@cindex @code{sabd@var{m}} instruction pattern
> +@item @samp{uabd@var{m}}, @samp{sabd@var{m}}
> +Signed and unsigned absolute difference instructions.  These
> +instructions find the difference between operands 1 and 2
> +then return the absolute value.  A C code equivalent would be:
> +@smallexample
> +op0 = op0 > op1 ? op0 - op1 : op1 - op0;

Should be:

  op0 = op1 > op2 ? op1 - op2 : op2 - op1;

since op0 is the output.

> +@end smallexample
> +
>  @cindex @code{avg@var{m}3_floor} instruction pattern
>  @cindex @code{uavg@var{m}3_floor} instruction pattern
>  @item @samp{avg@var{m}3_floor}
> diff --git a/gcc/internal-fn.def b/gcc/internal-fn.def
> index 7fe742c2ae713e7152ab05cfdfba86e4e0aa3456..0f1724ecf37a31c231572edf90b5577e2d82f468 100644
> --- a/gcc/internal-fn.def
> +++ b/gcc/internal-fn.def
> @@ -167,6 +167,9 @@ DEF_INTERNAL_OPTAB_FN (FMS, ECF_CONST, fms, ternary)
>  DEF_INTERNAL_OPTAB_FN (FNMA, ECF_CONST, fnma, ternary)
>  DEF_INTERNAL_OPTAB_FN (FNMS, ECF_CONST, fnms, ternary)
>  
> +DEF_INTERNAL_SIGNED_OPTAB_FN (ABD, ECF_CONST | ECF_NOTHROW, first,
> +			      sabd, uabd, binary)
> +
>  DEF_INTERNAL_SIGNED_OPTAB_FN (AVG_FLOOR, ECF_CONST | ECF_NOTHROW, first,
>  			      savg_floor, uavg_floor, binary)
>  DEF_INTERNAL_SIGNED_OPTAB_FN (AVG_CEIL, ECF_CONST | ECF_NOTHROW, first,
> diff --git a/gcc/optabs.def b/gcc/optabs.def
> index 695f5911b300c9ca5737de9be809fa01aabe5e01..29bc92281a2175f898634cbe6af63c18021e5268 100644
> --- a/gcc/optabs.def
> +++ b/gcc/optabs.def
> @@ -359,6 +359,8 @@ OPTAB_D (mask_fold_left_plus_optab, "mask_fold_left_plus_$a")
>  OPTAB_D (extract_last_optab, "extract_last_$a")
>  OPTAB_D (fold_extract_last_optab, "fold_extract_last_$a")
>  
> +OPTAB_D (uabd_optab, "uabd$a3")
> +OPTAB_D (sabd_optab, "sabd$a3")
>  OPTAB_D (savg_floor_optab, "avg$a3_floor")
>  OPTAB_D (uavg_floor_optab, "uavg$a3_floor")
>  OPTAB_D (savg_ceil_optab, "avg$a3_ceil")
> diff --git a/gcc/tree-vect-patterns.cc b/gcc/tree-vect-patterns.cc
> index a49b09539776c0056e77f99b10365d0a8747fbc5..50f1822f220c023027f4b0f777965f3757842fa2 100644
> --- a/gcc/tree-vect-patterns.cc
> +++ b/gcc/tree-vect-patterns.cc
> @@ -770,6 +770,93 @@ vect_split_statement (vec_info *vinfo, stmt_vec_info stmt2_info, tree new_rhs,
>      }
>  }
>  
> +/* Look for the following pattern
> +	X = x[i]
> +	Y = y[i]
> +	DIFF = X - Y
> +	DAD = ABS_EXPR<DIFF>
> +
> +   ABS_STMT should point to a statement of code ABS_EXPR or ABSU_EXPR.
> +   If REJECT_UNSIGNED is true it aborts if the type of ABS_STMT is unsigned.
> +   HALF_TYPE and UNPROM will be set should the statement be found to
> +   be a widened operation.
> +   DIFF_OPRNDS will be set to the two inputs of the MINUS_EXPR preceding
> +   ABS_STMT, otherwise it will be set the operations found by
> +   vect_widened_op_tree.
> + */
> +static bool
> +vect_recog_absolute_difference (vec_info *vinfo, gassign *abs_stmt,
> +				tree *half_type, bool reject_unsigned,
> +				vect_unpromoted_value unprom[2],
> +				tree diff_oprnds[2])
> +{
> +  if (!abs_stmt)
> +    return false;
> +
> +  /* FORNOW.  Can continue analyzing the def-use chain when this stmt in a phi
> +     inside the loop (in case we are analyzing an outer-loop).  */
> +  enum tree_code code = gimple_assign_rhs_code (abs_stmt);
> +  if (code != ABS_EXPR && code != ABSU_EXPR)
> +    return false;
> +
> +  tree abs_oprnd = gimple_assign_rhs1 (abs_stmt);
> +  tree abs_type = TREE_TYPE (abs_oprnd);
> +  if (!abs_oprnd)
> +    return false;
> +  if (reject_unsigned && TYPE_UNSIGNED (abs_type))
> +    return false;
> +  if (!ANY_INTEGRAL_TYPE_P (abs_type) || TYPE_OVERFLOW_WRAPS (abs_type))
> +    return false;

Could you explain the reject_unsigned behaviour?  I'd have expected
TYPE_OVERFLOW_WRAPS (abs_type) to reject the unsigned case anyway.

> +
> +  /* Peel off conversions from the ABS input.  This can involve sign
> +     changes (e.g.  from an unsigned subtraction to a signed ABS input)
> +     or signed promotion, but it can't include unsigned promotion.
> +     (Note that ABS of an unsigned promotion should have been folded
> +     away before now anyway.)  */

I'm not sure we can do the "unsigned subtraction to a signed ABS input"
case.  The code:

int
f (unsigned int x, int y)
{
  unsigned int diff = x - y;
  return __builtin_abs (diff);
}

is well-defined C (no undefined behaviour).  But it doesn't do the
same thing as an absolute difference.

So...

> +  vect_unpromoted_value unprom_diff;
> +  abs_oprnd = vect_look_through_possible_promotion (vinfo, abs_oprnd,
> +						    &unprom_diff);
> +  if (!abs_oprnd)
> +    return false;
> +  if (TYPE_PRECISION (unprom_diff.type) != TYPE_PRECISION (abs_type)
> +      && TYPE_UNSIGNED (unprom_diff.type)
> +      && TYPE_UNSIGNED (abs_type))
> +    return false;

...I think there are four valid cases:

(1) !TYPE_UNSIGNED (abs_type)
    && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (abs_oprnd))
    && TYPE_PRECISION (unprom_diff.type) == TYPE_PRECISION (abs_type)
    && regular unwidened MINUS_EXPR

    Here the subtraction and ABS input are signed.  We can assume that
    there is no signed overflow in the subtraction.

(2) !TYPE_UNSIGNED (abs_type)
    && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (abs_oprnd))
    && TYPE_PRECISION (unprom_diff.type) < TYPE_PRECISION (abs_type)
    && !TYPE_UNSIGNED (unprom_diff.type)
    && regular unwidened MINUS_EXPR

    This is like (1) except that the MINUS_EXPR result is sign-extended
    before the ABS.  Again we rely on having no signed overflow, hence the
    TYPE_OVERFLOW_UNDEFINED check on the subtraction type.  We can then
    push the sign-extension of the subtraction result “down” to the inputs
    of the subtraction.

(3) !TYPE_UNSIGNED (abs_type)
    && TYPE_PRECISION (unprom_diff.type) == TYPE_PRECISION (abs_type)
    && MINUS_EXPR of widened inputs

    In other words;

    - the ABS input is signed
    - the MINUS_EXPR has the same precision as the ABS
    - the MINUS_EXPR inputs are narrower than the result

    In this case the MINUS_EXPR is known to give correct results for
    all inputs, due to the extra range.  There's no need to rely on
    TYPE_OVERFLOW_UNDEFINED.

(4) !TYPE_UNSIGNED (abs_type)
    && TYPE_PRECISION (unprom_diff.type) < TYPE_PRECISION (abs_type)
    && !TYPE_UNSIGNED (unprom_diff.type)
    && MINUS_EXPR of widened inputs

    Like (3), but the subtraction result is further sign-extended
    (somewhat pointlessly).

Which is a very convoluated way of classifying it, sorry.

I think this means that:

(a) We should reject all cases in TYPE_UNSIGNED (abs_type) is true.
    Absolute values with unsigned inputs are a niche game, if they're
    valid at all.

(b) We should require TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (abs_oprnd))
    whenever we see a MINUS_EXPR with unextended inputs (i.e. whenever
    vect_widened_op_tree fails).

I guess some of this is really a comment about the existing SAD_EXPR code.

> +
> +  /* We then detect if the operand of abs_expr is defined by a minus_expr.  */
> +  stmt_vec_info diff_stmt_vinfo = vect_get_internal_def (vinfo, abs_oprnd);
> +  if (!diff_stmt_vinfo)
> +    return false;
> +
> +  /* FORNOW.  Can continue analyzing the def-use chain when this stmt in a phi
> +     inside the loop (in case we are analyzing an outer-loop).  */
> +  if (vect_widened_op_tree (vinfo, diff_stmt_vinfo, MINUS_EXPR,
> +			     WIDEN_MINUS_EXPR,
> +			     false, 2, unprom, half_type))
> +    {
> +      if (diff_oprnds)
> +	{
> +	  diff_oprnds[0] = unprom[0].op;
> +	  diff_oprnds[1] = unprom[1].op;
> +	}
> +      return true;
> +    }
> +
> +  // Failed to find a widen operation so we check for a regular MINUS_EXPR
> +  gassign *diff = dyn_cast <gassign *> (STMT_VINFO_STMT (diff_stmt_vinfo));
> +  if (diff_oprnds && diff && gimple_assign_rhs_code (diff) == MINUS_EXPR)
> +    {
> +      diff_oprnds[0] = gimple_assign_rhs1 (diff);
> +      diff_oprnds[1] = gimple_assign_rhs2 (diff);
> +    }
> +  else
> +    return false;
> +
> +  *half_type = NULL_TREE;
> +
> +  return true;

Very minor, but I think it'd be clearer to put the *half_type assignment
and return true in the "if" body, and unconditionally return false
at the end.  That makes it more consistent with the widening case.

> +}
> +
>  /* Convert UNPROM to TYPE and return the result, adding new statements
>     to STMT_INFO's pattern definition statements if no better way is
>     available.  VECTYPE is the vector form of TYPE.
> @@ -1308,40 +1395,13 @@ vect_recog_sad_pattern (vec_info *vinfo,
>    /* FORNOW.  Can continue analyzing the def-use chain when this stmt in a phi
>       inside the loop (in case we are analyzing an outer-loop).  */
>    gassign *abs_stmt = dyn_cast <gassign *> (abs_stmt_vinfo->stmt);
> -  if (!abs_stmt
> -      || (gimple_assign_rhs_code (abs_stmt) != ABS_EXPR
> -	  && gimple_assign_rhs_code (abs_stmt) != ABSU_EXPR))
> -    return NULL;
>  
> -  tree abs_oprnd = gimple_assign_rhs1 (abs_stmt);
> -  tree abs_type = TREE_TYPE (abs_oprnd);
> -  if (TYPE_UNSIGNED (abs_type))
> -    return NULL;
> -
> -  /* Peel off conversions from the ABS input.  This can involve sign
> -     changes (e.g. from an unsigned subtraction to a signed ABS input)
> -     or signed promotion, but it can't include unsigned promotion.
> -     (Note that ABS of an unsigned promotion should have been folded
> -     away before now anyway.)  */
> -  vect_unpromoted_value unprom_diff;
> -  abs_oprnd = vect_look_through_possible_promotion (vinfo, abs_oprnd,
> -						    &unprom_diff);
> -  if (!abs_oprnd)
> -    return NULL;
> -  if (TYPE_PRECISION (unprom_diff.type) != TYPE_PRECISION (abs_type)
> -      && TYPE_UNSIGNED (unprom_diff.type))
> -    return NULL;
> -
> -  /* We then detect if the operand of abs_expr is defined by a minus_expr.  */
> -  stmt_vec_info diff_stmt_vinfo = vect_get_internal_def (vinfo, abs_oprnd);
> -  if (!diff_stmt_vinfo)
> +  vect_unpromoted_value unprom[2];
> +  if (!vect_recog_absolute_difference (vinfo, abs_stmt, &half_type,
> +				       true, unprom, NULL))
>      return NULL;
>  
> -  /* FORNOW.  Can continue analyzing the def-use chain when this stmt in a phi
> -     inside the loop (in case we are analyzing an outer-loop).  */
> -  vect_unpromoted_value unprom[2];
> -  if (!vect_widened_op_tree (vinfo, diff_stmt_vinfo, MINUS_EXPR, WIDEN_MINUS_EXPR,
> -			     false, 2, unprom, &half_type))
> +  if (!half_type)
>      return NULL;
>  
>    vect_pattern_detected ("vect_recog_sad_pattern", last_stmt);
> @@ -1363,6 +1423,138 @@ vect_recog_sad_pattern (vec_info *vinfo,
>    return pattern_stmt;
>  }
>  
> +/* Function vect_recog_abd_pattern
> +
> +   Try to find the following ABsolute Difference (ABD) pattern:
> +
> +     VTYPE x, y, out;
> +     type diff;
> +   loop i in range:
> +     S1 diff = x[i] - y[i]
> +     S2 out[i] = ABS_EXPR <diff>;
> +
> +   where 'type' is a integer and 'VTYPE' is a vector of integers
> +   the same size as 'type'
> +
> +   Input:
> +
> +   * STMT_VINFO: The stmt from which the pattern search begins
> +
> +   Output:
> +
> +   * TYPE_out: The type of the output of this pattern
> +
> +   * Return value: A new stmt that will be used to replace the sequence of
> +     stmts that constitute the pattern; either SABD or UABD:
> +	SABD_EXPR<x, y, out>
> +	UABD_EXPR<x, y, out>
> +
> +      UABD expressions are used when the input types are
> +      narrower than the output types or the output type is narrower
> +      than 32 bits
> + */
> +
> +static gimple *
> +vect_recog_abd_pattern (vec_info *vinfo,
> +		stmt_vec_info stmt_vinfo, tree *type_out)
> +{
> +  /* Look for the following patterns
> +	X = x[i]
> +	Y = y[i]
> +	DIFF = X - Y
> +	DAD = ABS_EXPR<DIFF>
> +	out[i] = DAD
> +
> +     In which
> +      - X, Y, DIFF, DAD all have the same type
> +      - x, y, out are all vectors of the same type
> +  */
> +  gassign *last_stmt = dyn_cast <gassign *> (STMT_VINFO_STMT (stmt_vinfo));
> +  if (!last_stmt)
> +    return NULL;
> +
> +  tree out_type = TREE_TYPE (gimple_assign_lhs (last_stmt));
> +
> +  gassign *abs_stmt = last_stmt;
> +  if (gimple_assign_cast_p (last_stmt))
> +    {
> +      tree last_rhs = gimple_assign_rhs1 (last_stmt);
> +      if (!SSA_VAR_P (last_rhs))
> +	return NULL;
> +
> +      abs_stmt = dyn_cast <gassign *> (SSA_NAME_DEF_STMT (last_rhs));
> +      if (!abs_stmt)
> +	return NULL;
> +    }

Could you explain why this is needed?  I'd expect the function to be
called on the cast rhs too, so I wouldn't expect that we'd need to handle
casts explicitly.

> +  vect_unpromoted_value unprom[2];
> +  tree diff_oprnds[2];
> +  tree half_type;
> +  if (!vect_recog_absolute_difference (vinfo, abs_stmt, &half_type,
> +				       false, unprom, diff_oprnds))
> +    return NULL;
> +
> +#define SAME_TYPE(A, B) (TYPE_PRECISION (A) == TYPE_PRECISION (B))
> +
> +  tree abd_oprnds[2];
> +  if (half_type)
> +    {
> +      if (!SAME_TYPE (unprom[0].type, unprom[1].type))
> +	return NULL;

I wouldn't have expected this to be unecessary.  half_type is supposed
to be a common type that can hold all values of unprom[0].type and
unprom[1].type.  We should just be able to do:

> +      tree diff_type = TREE_TYPE (diff_oprnds[0]);
> +      if (TYPE_PRECISION (out_type) != TYPE_PRECISION (diff_type))
> +	{
> +	  tree vectype = get_vectype_for_scalar_type (vinfo, half_type);
> +	  vect_convert_inputs (vinfo, stmt_vinfo, 2, abd_oprnds,
> +			       half_type, unprom, vectype);

...this vect_convert_inputs unconditionally.  We need to check that
the get_vectype_for_scalar_type call succeeds though.

So does it work as:

  if (half_type)
    {
      tree vectype = get_vectype_for_scalar_type (vinfo, half_type);
      if (!vectype)
        return false;
      vect_convert_inputs (vinfo, stmt_vinfo, 2, abd_oprnds,
                           half_type, unprom, vectype);
    }

?

> +	}
> +      else
> +	{
> +	  abd_oprnds[0] = diff_oprnds[0];
> +	  abd_oprnds[1] = diff_oprnds[1];
> +	}
> +    }
> +  else
> +    {
> +      if (unprom[0].op && unprom[1].op
> +	  && (!SAME_TYPE (unprom[0].type, unprom[1].type)
> +	  || !SAME_TYPE (unprom[0].type, out_type)))
> +	return NULL;

AIUI, the !half_type case shouldn't look at unprom, since it's handling
simple MINUS_EXPRs.  I think we can just delete this "if" statement.

> +
> +      unprom[0].op = diff_oprnds[0];
> +      unprom[1].op = diff_oprnds[1];
> +      tree signed_out = signed_type_for (out_type);
> +      tree signed_out_vectype = get_vectype_for_scalar_type (vinfo, signed_out);

We need to check for success here too.

> +      vect_convert_inputs (vinfo, stmt_vinfo, 2, abd_oprnds,
> +			   signed_out, unprom, signed_out_vectype);
> +
> +      if (!SAME_TYPE (TREE_TYPE (diff_oprnds[0]), TREE_TYPE (abd_oprnds[0])))
> +	return NULL;

I don't think this is needed.

> +    }
> +
> +  if (!SAME_TYPE (TREE_TYPE (abd_oprnds[0]), TREE_TYPE (abd_oprnds[1]))
> +      || !SAME_TYPE (TREE_TYPE (abd_oprnds[0]), out_type))
> +    return NULL;

I also don't think this is needed.  AIUI, the previous code has done
all the necessary correctness checks.

> +
> +  vect_pattern_detected ("vect_recog_abd_pattern", last_stmt);
> +
> +  tree vectype = get_vectype_for_scalar_type (vinfo, out_type);

I think instead we want the vector types computed above.  That is:

- The ABD should be done on the vector version of half_type
  if the subtraction was on promoted inputs.  The result of
  the ABD should then be zero-extended (using vect_convert_output)
  to out_type.

  In particular, it's the sign of HALF_TYPE that decides whether
  it's signed or unsigned ABD.

- The ABD should be done on the vector version of signed_outtype
  if the subtraction was on unpromoted inputs.  We then might need
  to sign-cast it to outtype, if outtype is unsigned.  We can
  use vect_convert_output for that too.

  In other words, this case must use signed ABD.

Hope I've got that right...

Thanks,
Richard

> +  if (!vectype
> +      || !direct_internal_fn_supported_p (IFN_ABD, vectype,
> +					  OPTIMIZE_FOR_SPEED))
> +    return NULL;
> +
> +  *type_out = STMT_VINFO_VECTYPE (stmt_vinfo);
> +
> +  tree var = vect_recog_temp_ssa_var (out_type, NULL);
> +  gcall *abd_stmt = gimple_build_call_internal (IFN_ABD, 2,
> +						abd_oprnds[0], abd_oprnds[1]);
> +  gimple_call_set_lhs (abd_stmt, var);
> +  gimple_set_location (abd_stmt, gimple_location (last_stmt));
> +  return abd_stmt;
> +}
> +
>  /* Recognize an operation that performs ORIG_CODE on widened inputs,
>     so that it can be treated as though it had the form:
>  
> @@ -6439,6 +6631,7 @@ struct vect_recog_func
>  static vect_recog_func vect_vect_recog_func_ptrs[] = {
>    { vect_recog_bitfield_ref_pattern, "bitfield_ref" },
>    { vect_recog_bit_insert_pattern, "bit_insert" },
> +  { vect_recog_abd_pattern, "abd" },
>    { vect_recog_over_widening_pattern, "over_widening" },
>    /* Must come after over_widening, which narrows the shift as much as
>       possible beforehand.  */
  

On Thu, May 18, 2023 at 7:59 PM Richard Sandiford
<richard.sandiford@arm.com> wrote:
>
> Thanks for the update.  Some of these comments would have applied
> to the first version, so sorry for not catching them first time.
>
> <Oluwatamilore.Adebayo@arm.com> writes:
> > From: oluade01 <oluwatamilore.adebayo@arm.com>
> >
> > This adds a recognition pattern for the non-widening
> > absolute difference (ABD).
> >
> > gcc/ChangeLog:
> >
> >       * doc/md.texi (sabd, uabd): Document them.
> >       * internal-fn.def (ABD): Use new optab.
> >       * optabs.def (sabd_optab, uabd_optab): New optabs,
> >       * tree-vect-patterns.cc (vect_recog_absolute_difference):
> >       Recognize the following idiom abs (a - b).
> >       (vect_recog_sad_pattern): Refactor to use
> >       vect_recog_absolute_difference.
> >       (vect_recog_abd_pattern): Use patterns found by
> >       vect_recog_absolute_difference to build a new ABD
> >       internal call.
> > ---
> >  gcc/doc/md.texi           |  10 ++
> >  gcc/internal-fn.def       |   3 +
> >  gcc/optabs.def            |   2 +
> >  gcc/tree-vect-patterns.cc | 255 +++++++++++++++++++++++++++++++++-----
> >  4 files changed, 239 insertions(+), 31 deletions(-)
> >
> > diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi
> > index 07bf8bdebffb2e523f25a41f2b57e43c0276b745..3e65584d7efcd301f2c96a40edd82d30b84462b8 100644
> > --- a/gcc/doc/md.texi
> > +++ b/gcc/doc/md.texi
> > @@ -5778,6 +5778,16 @@ Other shift and rotate instructions, analogous to the
> >  Vector shift and rotate instructions that take vectors as operand 2
> >  instead of a scalar type.
> >
> > +@cindex @code{uabd@var{m}} instruction pattern
> > +@cindex @code{sabd@var{m}} instruction pattern
> > +@item @samp{uabd@var{m}}, @samp{sabd@var{m}}
> > +Signed and unsigned absolute difference instructions.  These
> > +instructions find the difference between operands 1 and 2
> > +then return the absolute value.  A C code equivalent would be:
> > +@smallexample
> > +op0 = op0 > op1 ? op0 - op1 : op1 - op0;
>
> Should be:
>
>   op0 = op1 > op2 ? op1 - op2 : op2 - op1;
>
> since op0 is the output.
>
> > +@end smallexample
> > +
> >  @cindex @code{avg@var{m}3_floor} instruction pattern
> >  @cindex @code{uavg@var{m}3_floor} instruction pattern
> >  @item @samp{avg@var{m}3_floor}
> > diff --git a/gcc/internal-fn.def b/gcc/internal-fn.def
> > index 7fe742c2ae713e7152ab05cfdfba86e4e0aa3456..0f1724ecf37a31c231572edf90b5577e2d82f468 100644
> > --- a/gcc/internal-fn.def
> > +++ b/gcc/internal-fn.def
> > @@ -167,6 +167,9 @@ DEF_INTERNAL_OPTAB_FN (FMS, ECF_CONST, fms, ternary)
> >  DEF_INTERNAL_OPTAB_FN (FNMA, ECF_CONST, fnma, ternary)
> >  DEF_INTERNAL_OPTAB_FN (FNMS, ECF_CONST, fnms, ternary)
> >
> > +DEF_INTERNAL_SIGNED_OPTAB_FN (ABD, ECF_CONST | ECF_NOTHROW, first,
> > +                           sabd, uabd, binary)
> > +
> >  DEF_INTERNAL_SIGNED_OPTAB_FN (AVG_FLOOR, ECF_CONST | ECF_NOTHROW, first,
> >                             savg_floor, uavg_floor, binary)
> >  DEF_INTERNAL_SIGNED_OPTAB_FN (AVG_CEIL, ECF_CONST | ECF_NOTHROW, first,
> > diff --git a/gcc/optabs.def b/gcc/optabs.def
> > index 695f5911b300c9ca5737de9be809fa01aabe5e01..29bc92281a2175f898634cbe6af63c18021e5268 100644
> > --- a/gcc/optabs.def
> > +++ b/gcc/optabs.def
> > @@ -359,6 +359,8 @@ OPTAB_D (mask_fold_left_plus_optab, "mask_fold_left_plus_$a")
> >  OPTAB_D (extract_last_optab, "extract_last_$a")
> >  OPTAB_D (fold_extract_last_optab, "fold_extract_last_$a")
> >
> > +OPTAB_D (uabd_optab, "uabd$a3")
> > +OPTAB_D (sabd_optab, "sabd$a3")
> >  OPTAB_D (savg_floor_optab, "avg$a3_floor")
> >  OPTAB_D (uavg_floor_optab, "uavg$a3_floor")
> >  OPTAB_D (savg_ceil_optab, "avg$a3_ceil")
> > diff --git a/gcc/tree-vect-patterns.cc b/gcc/tree-vect-patterns.cc
> > index a49b09539776c0056e77f99b10365d0a8747fbc5..50f1822f220c023027f4b0f777965f3757842fa2 100644
> > --- a/gcc/tree-vect-patterns.cc
> > +++ b/gcc/tree-vect-patterns.cc
> > @@ -770,6 +770,93 @@ vect_split_statement (vec_info *vinfo, stmt_vec_info stmt2_info, tree new_rhs,
> >      }
> >  }
> >
> > +/* Look for the following pattern
> > +     X = x[i]
> > +     Y = y[i]
> > +     DIFF = X - Y
> > +     DAD = ABS_EXPR<DIFF>
> > +
> > +   ABS_STMT should point to a statement of code ABS_EXPR or ABSU_EXPR.
> > +   If REJECT_UNSIGNED is true it aborts if the type of ABS_STMT is unsigned.
> > +   HALF_TYPE and UNPROM will be set should the statement be found to
> > +   be a widened operation.
> > +   DIFF_OPRNDS will be set to the two inputs of the MINUS_EXPR preceding
> > +   ABS_STMT, otherwise it will be set the operations found by
> > +   vect_widened_op_tree.
> > + */
> > +static bool
> > +vect_recog_absolute_difference (vec_info *vinfo, gassign *abs_stmt,
> > +                             tree *half_type, bool reject_unsigned,
> > +                             vect_unpromoted_value unprom[2],
> > +                             tree diff_oprnds[2])
> > +{
> > +  if (!abs_stmt)
> > +    return false;
> > +
> > +  /* FORNOW.  Can continue analyzing the def-use chain when this stmt in a phi
> > +     inside the loop (in case we are analyzing an outer-loop).  */
> > +  enum tree_code code = gimple_assign_rhs_code (abs_stmt);
> > +  if (code != ABS_EXPR && code != ABSU_EXPR)
> > +    return false;
> > +
> > +  tree abs_oprnd = gimple_assign_rhs1 (abs_stmt);
> > +  tree abs_type = TREE_TYPE (abs_oprnd);
> > +  if (!abs_oprnd)
> > +    return false;
> > +  if (reject_unsigned && TYPE_UNSIGNED (abs_type))
> > +    return false;
> > +  if (!ANY_INTEGRAL_TYPE_P (abs_type) || TYPE_OVERFLOW_WRAPS (abs_type))
> > +    return false;
>
> Could you explain the reject_unsigned behaviour?  I'd have expected
> TYPE_OVERFLOW_WRAPS (abs_type) to reject the unsigned case anyway.
>
> > +
> > +  /* Peel off conversions from the ABS input.  This can involve sign
> > +     changes (e.g.  from an unsigned subtraction to a signed ABS input)
> > +     or signed promotion, but it can't include unsigned promotion.
> > +     (Note that ABS of an unsigned promotion should have been folded
> > +     away before now anyway.)  */
>
> I'm not sure we can do the "unsigned subtraction to a signed ABS input"
> case.  The code:
>
> int
> f (unsigned int x, int y)
> {
>   unsigned int diff = x - y;
>   return __builtin_abs (diff);
> }
>
> is well-defined C (no undefined behaviour).  But it doesn't do the
> same thing as an absolute difference.
>
> So...
>
> > +  vect_unpromoted_value unprom_diff;
> > +  abs_oprnd = vect_look_through_possible_promotion (vinfo, abs_oprnd,
> > +                                                 &unprom_diff);
> > +  if (!abs_oprnd)
> > +    return false;
> > +  if (TYPE_PRECISION (unprom_diff.type) != TYPE_PRECISION (abs_type)
> > +      && TYPE_UNSIGNED (unprom_diff.type)
> > +      && TYPE_UNSIGNED (abs_type))
> > +    return false;
>
> ...I think there are four valid cases:
>
> (1) !TYPE_UNSIGNED (abs_type)
>     && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (abs_oprnd))
>     && TYPE_PRECISION (unprom_diff.type) == TYPE_PRECISION (abs_type)
>     && regular unwidened MINUS_EXPR
>
>     Here the subtraction and ABS input are signed.  We can assume that
>     there is no signed overflow in the subtraction.
>
> (2) !TYPE_UNSIGNED (abs_type)
>     && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (abs_oprnd))
>     && TYPE_PRECISION (unprom_diff.type) < TYPE_PRECISION (abs_type)
>     && !TYPE_UNSIGNED (unprom_diff.type)
>     && regular unwidened MINUS_EXPR
>
>     This is like (1) except that the MINUS_EXPR result is sign-extended
>     before the ABS.  Again we rely on having no signed overflow, hence the
>     TYPE_OVERFLOW_UNDEFINED check on the subtraction type.  We can then
>     push the sign-extension of the subtraction result “down” to the inputs
>     of the subtraction.
>
> (3) !TYPE_UNSIGNED (abs_type)
>     && TYPE_PRECISION (unprom_diff.type) == TYPE_PRECISION (abs_type)
>     && MINUS_EXPR of widened inputs
>
>     In other words;
>
>     - the ABS input is signed
>     - the MINUS_EXPR has the same precision as the ABS
>     - the MINUS_EXPR inputs are narrower than the result
>
>     In this case the MINUS_EXPR is known to give correct results for
>     all inputs, due to the extra range.  There's no need to rely on
>     TYPE_OVERFLOW_UNDEFINED.
>
> (4) !TYPE_UNSIGNED (abs_type)
>     && TYPE_PRECISION (unprom_diff.type) < TYPE_PRECISION (abs_type)
>     && !TYPE_UNSIGNED (unprom_diff.type)
>     && MINUS_EXPR of widened inputs
>
>     Like (3), but the subtraction result is further sign-extended
>     (somewhat pointlessly).
>
> Which is a very convoluated way of classifying it, sorry.

There's also the possibility that you see ABSU_EXPR instead of ABS_EXPR.

> I think this means that:
>
> (a) We should reject all cases in TYPE_UNSIGNED (abs_type) is true.
>     Absolute values with unsigned inputs are a niche game, if they're
>     valid at all.
>
> (b) We should require TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (abs_oprnd))
>     whenever we see a MINUS_EXPR with unextended inputs (i.e. whenever
>     vect_widened_op_tree fails).
>
> I guess some of this is really a comment about the existing SAD_EXPR code.
>
> > +
> > +  /* We then detect if the operand of abs_expr is defined by a minus_expr.  */
> > +  stmt_vec_info diff_stmt_vinfo = vect_get_internal_def (vinfo, abs_oprnd);
> > +  if (!diff_stmt_vinfo)
> > +    return false;
> > +
> > +  /* FORNOW.  Can continue analyzing the def-use chain when this stmt in a phi
> > +     inside the loop (in case we are analyzing an outer-loop).  */
> > +  if (vect_widened_op_tree (vinfo, diff_stmt_vinfo, MINUS_EXPR,
> > +                          WIDEN_MINUS_EXPR,
> > +                          false, 2, unprom, half_type))
> > +    {
> > +      if (diff_oprnds)
> > +     {
> > +       diff_oprnds[0] = unprom[0].op;
> > +       diff_oprnds[1] = unprom[1].op;
> > +     }
> > +      return true;
> > +    }
> > +
> > +  // Failed to find a widen operation so we check for a regular MINUS_EXPR
> > +  gassign *diff = dyn_cast <gassign *> (STMT_VINFO_STMT (diff_stmt_vinfo));
> > +  if (diff_oprnds && diff && gimple_assign_rhs_code (diff) == MINUS_EXPR)
> > +    {
> > +      diff_oprnds[0] = gimple_assign_rhs1 (diff);
> > +      diff_oprnds[1] = gimple_assign_rhs2 (diff);
> > +    }
> > +  else
> > +    return false;
> > +
> > +  *half_type = NULL_TREE;
> > +
> > +  return true;
>
> Very minor, but I think it'd be clearer to put the *half_type assignment
> and return true in the "if" body, and unconditionally return false
> at the end.  That makes it more consistent with the widening case.
>
> > +}
> > +
> >  /* Convert UNPROM to TYPE and return the result, adding new statements
> >     to STMT_INFO's pattern definition statements if no better way is
> >     available.  VECTYPE is the vector form of TYPE.
> > @@ -1308,40 +1395,13 @@ vect_recog_sad_pattern (vec_info *vinfo,
> >    /* FORNOW.  Can continue analyzing the def-use chain when this stmt in a phi
> >       inside the loop (in case we are analyzing an outer-loop).  */
> >    gassign *abs_stmt = dyn_cast <gassign *> (abs_stmt_vinfo->stmt);
> > -  if (!abs_stmt
> > -      || (gimple_assign_rhs_code (abs_stmt) != ABS_EXPR
> > -       && gimple_assign_rhs_code (abs_stmt) != ABSU_EXPR))
> > -    return NULL;
> >
> > -  tree abs_oprnd = gimple_assign_rhs1 (abs_stmt);
> > -  tree abs_type = TREE_TYPE (abs_oprnd);
> > -  if (TYPE_UNSIGNED (abs_type))
> > -    return NULL;
> > -
> > -  /* Peel off conversions from the ABS input.  This can involve sign
> > -     changes (e.g. from an unsigned subtraction to a signed ABS input)
> > -     or signed promotion, but it can't include unsigned promotion.
> > -     (Note that ABS of an unsigned promotion should have been folded
> > -     away before now anyway.)  */
> > -  vect_unpromoted_value unprom_diff;
> > -  abs_oprnd = vect_look_through_possible_promotion (vinfo, abs_oprnd,
> > -                                                 &unprom_diff);
> > -  if (!abs_oprnd)
> > -    return NULL;
> > -  if (TYPE_PRECISION (unprom_diff.type) != TYPE_PRECISION (abs_type)
> > -      && TYPE_UNSIGNED (unprom_diff.type))
> > -    return NULL;
> > -
> > -  /* We then detect if the operand of abs_expr is defined by a minus_expr.  */
> > -  stmt_vec_info diff_stmt_vinfo = vect_get_internal_def (vinfo, abs_oprnd);
> > -  if (!diff_stmt_vinfo)
> > +  vect_unpromoted_value unprom[2];
> > +  if (!vect_recog_absolute_difference (vinfo, abs_stmt, &half_type,
> > +                                    true, unprom, NULL))
> >      return NULL;
> >
> > -  /* FORNOW.  Can continue analyzing the def-use chain when this stmt in a phi
> > -     inside the loop (in case we are analyzing an outer-loop).  */
> > -  vect_unpromoted_value unprom[2];
> > -  if (!vect_widened_op_tree (vinfo, diff_stmt_vinfo, MINUS_EXPR, WIDEN_MINUS_EXPR,
> > -                          false, 2, unprom, &half_type))
> > +  if (!half_type)
> >      return NULL;
> >
> >    vect_pattern_detected ("vect_recog_sad_pattern", last_stmt);
> > @@ -1363,6 +1423,138 @@ vect_recog_sad_pattern (vec_info *vinfo,
> >    return pattern_stmt;
> >  }
> >
> > +/* Function vect_recog_abd_pattern
> > +
> > +   Try to find the following ABsolute Difference (ABD) pattern:
> > +
> > +     VTYPE x, y, out;
> > +     type diff;
> > +   loop i in range:
> > +     S1 diff = x[i] - y[i]
> > +     S2 out[i] = ABS_EXPR <diff>;
> > +
> > +   where 'type' is a integer and 'VTYPE' is a vector of integers
> > +   the same size as 'type'
> > +
> > +   Input:
> > +
> > +   * STMT_VINFO: The stmt from which the pattern search begins
> > +
> > +   Output:
> > +
> > +   * TYPE_out: The type of the output of this pattern
> > +
> > +   * Return value: A new stmt that will be used to replace the sequence of
> > +     stmts that constitute the pattern; either SABD or UABD:
> > +     SABD_EXPR<x, y, out>
> > +     UABD_EXPR<x, y, out>
> > +
> > +      UABD expressions are used when the input types are
> > +      narrower than the output types or the output type is narrower
> > +      than 32 bits
> > + */
> > +
> > +static gimple *
> > +vect_recog_abd_pattern (vec_info *vinfo,
> > +             stmt_vec_info stmt_vinfo, tree *type_out)
> > +{
> > +  /* Look for the following patterns
> > +     X = x[i]
> > +     Y = y[i]
> > +     DIFF = X - Y
> > +     DAD = ABS_EXPR<DIFF>
> > +     out[i] = DAD
> > +
> > +     In which
> > +      - X, Y, DIFF, DAD all have the same type
> > +      - x, y, out are all vectors of the same type
> > +  */
> > +  gassign *last_stmt = dyn_cast <gassign *> (STMT_VINFO_STMT (stmt_vinfo));
> > +  if (!last_stmt)
> > +    return NULL;
> > +
> > +  tree out_type = TREE_TYPE (gimple_assign_lhs (last_stmt));
> > +
> > +  gassign *abs_stmt = last_stmt;
> > +  if (gimple_assign_cast_p (last_stmt))
> > +    {
> > +      tree last_rhs = gimple_assign_rhs1 (last_stmt);
> > +      if (!SSA_VAR_P (last_rhs))
> > +     return NULL;
> > +
> > +      abs_stmt = dyn_cast <gassign *> (SSA_NAME_DEF_STMT (last_rhs));
> > +      if (!abs_stmt)
> > +     return NULL;
> > +    }
>
> Could you explain why this is needed?  I'd expect the function to be
> called on the cast rhs too, so I wouldn't expect that we'd need to handle
> casts explicitly.
>
> > +  vect_unpromoted_value unprom[2];
> > +  tree diff_oprnds[2];
> > +  tree half_type;
> > +  if (!vect_recog_absolute_difference (vinfo, abs_stmt, &half_type,
> > +                                    false, unprom, diff_oprnds))
> > +    return NULL;
> > +
> > +#define SAME_TYPE(A, B) (TYPE_PRECISION (A) == TYPE_PRECISION (B))
> > +
> > +  tree abd_oprnds[2];
> > +  if (half_type)
> > +    {
> > +      if (!SAME_TYPE (unprom[0].type, unprom[1].type))
> > +     return NULL;
>
> I wouldn't have expected this to be unecessary.  half_type is supposed
> to be a common type that can hold all values of unprom[0].type and
> unprom[1].type.  We should just be able to do:
>
> > +      tree diff_type = TREE_TYPE (diff_oprnds[0]);
> > +      if (TYPE_PRECISION (out_type) != TYPE_PRECISION (diff_type))
> > +     {
> > +       tree vectype = get_vectype_for_scalar_type (vinfo, half_type);
> > +       vect_convert_inputs (vinfo, stmt_vinfo, 2, abd_oprnds,
> > +                            half_type, unprom, vectype);
>
> ...this vect_convert_inputs unconditionally.  We need to check that
> the get_vectype_for_scalar_type call succeeds though.
>
> So does it work as:
>
>   if (half_type)
>     {
>       tree vectype = get_vectype_for_scalar_type (vinfo, half_type);
>       if (!vectype)
>         return false;
>       vect_convert_inputs (vinfo, stmt_vinfo, 2, abd_oprnds,
>                            half_type, unprom, vectype);
>     }
>
> ?
>
> > +     }
> > +      else
> > +     {
> > +       abd_oprnds[0] = diff_oprnds[0];
> > +       abd_oprnds[1] = diff_oprnds[1];
> > +     }
> > +    }
> > +  else
> > +    {
> > +      if (unprom[0].op && unprom[1].op
> > +       && (!SAME_TYPE (unprom[0].type, unprom[1].type)
> > +       || !SAME_TYPE (unprom[0].type, out_type)))
> > +     return NULL;
>
> AIUI, the !half_type case shouldn't look at unprom, since it's handling
> simple MINUS_EXPRs.  I think we can just delete this "if" statement.
>
> > +
> > +      unprom[0].op = diff_oprnds[0];
> > +      unprom[1].op = diff_oprnds[1];
> > +      tree signed_out = signed_type_for (out_type);
> > +      tree signed_out_vectype = get_vectype_for_scalar_type (vinfo, signed_out);
>
> We need to check for success here too.
>
> > +      vect_convert_inputs (vinfo, stmt_vinfo, 2, abd_oprnds,
> > +                        signed_out, unprom, signed_out_vectype);
> > +
> > +      if (!SAME_TYPE (TREE_TYPE (diff_oprnds[0]), TREE_TYPE (abd_oprnds[0])))
> > +     return NULL;
>
> I don't think this is needed.
>
> > +    }
> > +
> > +  if (!SAME_TYPE (TREE_TYPE (abd_oprnds[0]), TREE_TYPE (abd_oprnds[1]))
> > +      || !SAME_TYPE (TREE_TYPE (abd_oprnds[0]), out_type))
> > +    return NULL;
>
> I also don't think this is needed.  AIUI, the previous code has done
> all the necessary correctness checks.
>
> > +
> > +  vect_pattern_detected ("vect_recog_abd_pattern", last_stmt);
> > +
> > +  tree vectype = get_vectype_for_scalar_type (vinfo, out_type);
>
> I think instead we want the vector types computed above.  That is:
>
> - The ABD should be done on the vector version of half_type
>   if the subtraction was on promoted inputs.  The result of
>   the ABD should then be zero-extended (using vect_convert_output)
>   to out_type.
>
>   In particular, it's the sign of HALF_TYPE that decides whether
>   it's signed or unsigned ABD.
>
> - The ABD should be done on the vector version of signed_outtype
>   if the subtraction was on unpromoted inputs.  We then might need
>   to sign-cast it to outtype, if outtype is unsigned.  We can
>   use vect_convert_output for that too.
>
>   In other words, this case must use signed ABD.
>
> Hope I've got that right...
>
> Thanks,
> Richard
>
> > +  if (!vectype
> > +      || !direct_internal_fn_supported_p (IFN_ABD, vectype,
> > +                                       OPTIMIZE_FOR_SPEED))
> > +    return NULL;
> > +
> > +  *type_out = STMT_VINFO_VECTYPE (stmt_vinfo);
> > +
> > +  tree var = vect_recog_temp_ssa_var (out_type, NULL);
> > +  gcall *abd_stmt = gimple_build_call_internal (IFN_ABD, 2,
> > +                                             abd_oprnds[0], abd_oprnds[1]);
> > +  gimple_call_set_lhs (abd_stmt, var);
> > +  gimple_set_location (abd_stmt, gimple_location (last_stmt));
> > +  return abd_stmt;
> > +}
> > +
> >  /* Recognize an operation that performs ORIG_CODE on widened inputs,
> >     so that it can be treated as though it had the form:
> >
> > @@ -6439,6 +6631,7 @@ struct vect_recog_func
> >  static vect_recog_func vect_vect_recog_func_ptrs[] = {
> >    { vect_recog_bitfield_ref_pattern, "bitfield_ref" },
> >    { vect_recog_bit_insert_pattern, "bit_insert" },
> > +  { vect_recog_abd_pattern, "abd" },
> >    { vect_recog_over_widening_pattern, "over_widening" },
> >    /* Must come after over_widening, which narrows the shift as much as
> >       possible beforehand.  */
  

> > +  if (reject_unsigned && TYPE_UNSIGNED (abs_type))
> > +    return false;
> > +  if (!ANY_INTEGRAL_TYPE_P (abs_type) || TYPE_OVERFLOW_WRAPS (abs_type))
> > +    return false;
> 
> Could you explain the reject_unsigned behaviour?  I'd have expected
> TYPE_OVERFLOW_WRAPS (abs_type) to reject the unsigned case anyway.

When REJECT_UNSIGNED is true, cases wherein the abs type is unsigned or when the
unpromoted diff type is both not equal in precision to the abs type and unsigned
the statement is rejected.

vect_recog_absolute_difference replaces some of the logic in vect_recog_sad_pattern
and is used by vect_recog_abd_pattern.
vect_recog_sad_pattern aborts if the abs type is unsigned or when the unprom
diff type isn't the same precision as abs type and unsigned.
vect_recog_abd_pattern doesn't do the same, so REJECT_UNSIGNED is a flag for this.

I found it to be unnecessary as you suggested, so it's been dropped.

> > +  if (half_type)
> > +    {
> > +      if (!SAME_TYPE (unprom[0].type, unprom[1].type))
> > +	return NULL;
> 
> I wouldn't have expected this to be unecessary.  half_type is supposed
> to be a common type that can hold all values of unprom[0].type and
> unprom[1].type.  We should just be able to do:
> 
> > +      tree diff_type = TREE_TYPE (diff_oprnds[0]);
> > +      if (TYPE_PRECISION (out_type) != TYPE_PRECISION (diff_type))
> > +	{
> > +	  tree vectype = get_vectype_for_scalar_type (vinfo, half_type);
> > +	  vect_convert_inputs (vinfo, stmt_vinfo, 2, abd_oprnds,
> > +			       half_type, unprom, vectype);
> 
> ...this vect_convert_inputs unconditionally.  We need to check that
> the get_vectype_for_scalar_type call succeeds though.
> 
> So does it work as:
> 
>   if (half_type)
>     {
>       tree vectype = get_vectype_for_scalar_type (vinfo, half_type);
>       if (!vectype)
>         return false;
>       vect_convert_inputs (vinfo, stmt_vinfo, 2, abd_oprnds,
>                            half_type, unprom, vectype);
>     }
> 
> ?

The proposed solution works.

> > +	}
> > +      else
> > +	{
> > +	  abd_oprnds[0] = diff_oprnds[0];
> > +	  abd_oprnds[1] = diff_oprnds[1];
> > +	}
> > +    }
> > +  else
> > +    {
> > +      if (unprom[0].op && unprom[1].op
> > +	  && (!SAME_TYPE (unprom[0].type, unprom[1].type)
> > +	  || !SAME_TYPE (unprom[0].type, out_type)))
> > +	return NULL;
> 
> AIUI, the !half_type case shouldn't look at unprom, since it's handling
> simple MINUS_EXPRs.  I think we can just delete this "if" statement.

If statement removed.

> > +      unprom[0].op = diff_oprnds[0];
> > +      unprom[1].op = diff_oprnds[1];
> > +      tree signed_out = signed_type_for (out_type);
> > +      tree signed_out_vectype = get_vectype_for_scalar_type (vinfo, signed_out);
> 
> We need to check for success here too.

Add a check.

> > +      vect_convert_inputs (vinfo, stmt_vinfo, 2, abd_oprnds,
> > +			   signed_out, unprom, signed_out_vectype);
> > +
> > +      if (!SAME_TYPE (TREE_TYPE (diff_oprnds[0]), TREE_TYPE (abd_oprnds[0])))
> > +	return NULL;
> 
> I don't think this is needed.

Statement removed.

> > +    }
> > +
> > +  if (!SAME_TYPE (TREE_TYPE (abd_oprnds[0]), TREE_TYPE (abd_oprnds[1]))
> > +      || !SAME_TYPE (TREE_TYPE (abd_oprnds[0]), out_type))
> > +    return NULL;
> 
> I also don't think this is needed.  AIUI, the previous code has done
> all the necessary correctness checks.

Statements removed.

> > +  vect_pattern_detected ("vect_recog_abd_pattern", last_stmt);
> > +
> > +  tree vectype = get_vectype_for_scalar_type (vinfo, out_type);
> 
> I think instead we want the vector types computed above.  That is:
> 
> - The ABD should be done on the vector version of half_type
>   if the subtraction was on promoted inputs.  The result of
>   the ABD should then be zero-extended (using vect_convert_output)
>   to out_type.
> 
>   In particular, it's the sign of HALF_TYPE that decides whether
>   it's signed or unsigned ABD.
> 
> - The ABD should be done on the vector version of signed_outtype
>   if the subtraction was on unpromoted inputs.  We then might need
>   to sign-cast it to outtype, if outtype is unsigned.  We can
>   use vect_convert_output for that too.
> 
>   In other words, this case must use signed ABD.

In the half_type case out_type is set to be half_type.

Patch is in the next response.