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, 7 insertions, 1 deletions

diff --git a/gcc/tree-vect-loop.c b/gcc/tree-vect-loop.c
index e978015..fc3dab0 100644
--- a/gcc/tree-vect-loop.c
+++ b/gcc/tree-vect-loop.c
@@ -6661,6 +6661,12 @@ vectorizable_reduction (loop_vec_info loop_vinfo,
   bool lane_reduc_code_p
     = (code == DOT_PROD_EXPR || code == WIDEN_SUM_EXPR || code == SAD_EXPR);
   int op_type = TREE_CODE_LENGTH (code);
+  enum optab_subtype optab_query_kind = optab_vector;
+  if (code == DOT_PROD_EXPR
+      && TYPE_SIGN (TREE_TYPE (gimple_assign_rhs1 (stmt)))
+	   != TYPE_SIGN (TREE_TYPE (gimple_assign_rhs2 (stmt))))
+    optab_query_kind = optab_vector_mixed_sign;
+
 
   scalar_dest = gimple_assign_lhs (stmt);
   scalar_type = TREE_TYPE (scalar_dest);
@@ -7189,7 +7195,7 @@ vectorizable_reduction (loop_vec_info loop_vinfo,
       bool ok = true;
 
       /* 4.1. check support for the operation in the loop  */
-      optab optab = optab_for_tree_code (code, vectype_in, optab_vector);
+      optab optab = optab_for_tree_code (code, vectype_in, optab_query_kind);
       if (!optab)
 	{
 	  if (dump_enabled_p ())