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From: Richard Sandiford <richard.sandiford@arm.com>
To: Richard Biener <richard.guenther@gmail.com>
Mail-Followup-To: Richard Biener <richard.guenther@gmail.com>,
 liuhongt <hongtao.liu@intel.com>, GCC Patches <gcc-patches@gcc.gnu.org>,
 richard.sandiford@arm.com
Cc: liuhongt <hongtao.liu@intel.com>,  GCC Patches <gcc-patches@gcc.gnu.org>
Subject: Re: [RFC: PATCH] Extend vectorizer to handle nonlinear induction for
 neg, mul/lshift/rshift with a constant.
References: <20220804042839.49603-1-hongtao.liu@intel.com>
 <CAFiYyc3b3UPqA453TUZt-__bScoPfK29MOVO7Bnj4_J3_fYpFw@mail.gmail.com>
Date: Thu, 04 Aug 2022 11:09:27 +0100
In-Reply-To: <CAFiYyc3b3UPqA453TUZt-__bScoPfK29MOVO7Bnj4_J3_fYpFw@mail.gmail.com>
 (Richard Biener's message of "Thu, 4 Aug 2022 10:18:26 +0200")
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Richard Biener <richard.guenther@gmail.com> writes:
>> +/* Create vector init for vectorized iv.  */
>> +static tree
>> +vect_create_nonlinear_iv_init (gimple_seq* stmts, tree init_expr,
>> +                              tree step_expr, poly_uint64 nunits,
>> +                              tree vectype,
>> +                              enum vect_induction_op_type induction_type)
>> +{
>> +  unsigned HOST_WIDE_INT const_nunits;
>> +  tree vec_shift, vec_init, new_name;
>> +  unsigned i;
>> +
>> +  /* iv_loop is the loop to be vectorized. Create:
>> +     vec_init = [X, X+S, X+2*S, X+3*S] (S = step_expr, X = init_expr).  */
>> +  new_name = init_expr;
>> +  switch (induction_type)
>> +    {
>> +    case vect_step_op_shr:
>> +    case vect_step_op_shl:
>> +      /* Build the Initial value from shift_expr.  */
>> +      vec_init = gimple_build_vector_from_val (stmts,
>> +                                              vectype,
>> +                                              new_name);
>> +      vec_shift = gimple_build (stmts, VEC_SERIES_EXPR, vectype,
>> +                               build_zero_cst (TREE_TYPE (step_expr)),
>> +                               step_expr);
>
> There might be a more canonical way to build the series expr - Richard?

build_vec_series is shorter if step_expr is known to be a constant.
The above looks good for the general case.

Thanks,
Richard