Vect: Add support for dot-product where the sign for the multiplicant changes.

This patch adds support for a dot product where the sign of the multiplication
arguments differ. i.e. one is signed and one is unsigned but the precisions are
the same.

#define N 480
#define SIGNEDNESS_1 unsigned
#define SIGNEDNESS_2 signed
#define SIGNEDNESS_3 signed
#define SIGNEDNESS_4 unsigned

SIGNEDNESS_1 int __attribute__ ((noipa))
f (SIGNEDNESS_1 int res, SIGNEDNESS_3 char *restrict a,
   SIGNEDNESS_4 char *restrict b)
{
  for (__INTPTR_TYPE__ i = 0; i < N; ++i)
    {
      int av = a[i];
      int bv = b[i];
      SIGNEDNESS_2 short mult = av * bv;
      res += mult;
    }
  return res;
}

The operations are performed as if the operands were extended to a 32-bit value.
As such this operation isn't valid if there is an intermediate conversion to an
unsigned value. i.e.  if SIGNEDNESS_2 is unsigned.

more over if the signs of SIGNEDNESS_3 and SIGNEDNESS_4 are flipped the same
optab is used but the operands are flipped in the optab expansion.

To support this the patch extends the dot-product detection to optionally
ignore operands with different signs and stores this information in the optab
subtype which is now made a bitfield.

The subtype can now additionally controls which optab an EXPR can expand to.

gcc/ChangeLog:

	* optabs.def (usdot_prod_optab): New.
	* doc/md.texi: Document it and clarify other dot prod optabs.
	* optabs-tree.h (enum optab_subtype): Add optab_vector_mixed_sign.
	* optabs-tree.c (optab_for_tree_code): Support usdot_prod_optab.
	* optabs.c (expand_widen_pattern_expr): Likewise.
	* tree-cfg.c (verify_gimple_assign_ternary): Likewise.
	* tree-vect-loop.c (vectorizable_reduction): Query dot-product kind.
	* tree-vect-patterns.c (vect_supportable_direct_optab_p): Take optional
	optab subtype.
	(vect_widened_op_tree): Optionally ignore
	mismatch types.
	(vect_recog_dot_prod_pattern): Support usdot_prod_optab.

1 files changed, 2 insertions, 1 deletions

diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c
index 1f0f4a2..2820847 100644
--- a/gcc/tree-cfg.c
+++ b/gcc/tree-cfg.c
@@ -4438,7 +4438,8 @@ verify_gimple_assign_ternary (gassign *stmt)
 		  && !SCALAR_FLOAT_TYPE_P (rhs1_type))
 		 || (!INTEGRAL_TYPE_P (lhs_type)
 		     && !SCALAR_FLOAT_TYPE_P (lhs_type))))
-	    || !types_compatible_p (rhs1_type, rhs2_type)
+	    /* rhs1_type and rhs2_type may differ in sign.  */
+	    || !tree_nop_conversion_p (rhs1_type, rhs2_type)
 	    || !useless_type_conversion_p (lhs_type, rhs3_type)
 	    || maybe_lt (GET_MODE_SIZE (element_mode (rhs3_type)),
 			 2 * GET_MODE_SIZE (element_mode (rhs1_type))))