Hi,

The vectorizer expects widening multiplication pattern to be:

     type a_t, b_t;
     TYPE a_T, b_T, prod_T;

     a_T = (TYPE) a_t;
     b_T = (TYPE) b_t;
     prod_T = a_T * b_T;

where type 'TYPE' is double the size of type 'type'. This works fine
when the types are signed. For the unsigned types the code looks like:

     unsigned type a_t, b_t;
     unsigned TYPE u_prod_T;
     TYPE a_T, b_T, prod_T;

      a_T = (TYPE) a_t;
      b_T = (TYPE) b_t;
      prod_T = a_T * b_T;
      u_prod_T = (unsigned TYPE) prod_T;

i.e., the multiplication is done on signed, followed by a cast to unsigned.
This patch adds a support of such patterns and generates
WIDEN_MULT_EXPR for the unsigned type.

Another unsupported case is multiplication by a constant (e.g., b_T is
a constant). This patch checks that the constant fits the smaller type
'type' and recognizes such cases as widening multiplication.

Bootstrapped and tested on powerpc64-suse-linux. Tested the
vectorization testsuite on arm-linux-gnueabi.
I'll commit the patch shortly if there are no comments/objections.

Ira

ChangeLog:

       * tree-vectorizer.h (vect_recog_func_ptr): Make last argument to be
       a pointer.
       * tree-vect-patterns.c (vect_recog_widen_sum_pattern,
       vect_recog_widen_mult_pattern, vect_recog_dot_prod_pattern,
       vect_recog_pow_pattern): Likewise.
       (vect_pattern_recog_1): Remove declaration.
       (widened_name_p): Remove declaration.  Add new argument to specify
       whether to check that both types are either signed or unsigned.
       (vect_recog_widen_mult_pattern): Update documentation.  Handle
       unsigned patterns and multiplication by constants.
       (vect_pattern_recog_1): Update vect_recog_func references.  Use
       statement information from the statement returned from pattern
       detection functions.
       (vect_pattern_recog): Update vect_recog_func reference.
       * tree-vect-stmts.c (vectorizable_type_promotion): For widening
       multiplication by a constant use the type of the other operand.

testsuite/ChangeLog:

       * lib/target-supports.exp
(check_effective_target_vect_widen_mult_qi_to_hi):
       Add NEON as supporting target.
       (check_effective_target_vect_widen_mult_hi_to_si): Likewise.
       (check_effective_target_vect_widen_mult_qi_to_hi_pattern): New.
       (check_effective_target_vect_widen_mult_hi_to_si_pattern): New.
       * gcc.dg/vect/vect-widen-mult-u8.c: Expect to be vectorized
using widening
       multiplication on targets that support it.
       * gcc.dg/vect/vect-widen-mult-u16.c: Likewise.
       * gcc.dg/vect/vect-widen-mult-const-s16.c: New test.
       * gcc.dg/vect/vect-widen-mult-const-u16.c: New test.