Re: [PATCH V4] VECT: Add decrement IV iteration loop control by variable amount support

[Richard Sandiford <richard.sandiford@arm.com>]

钟居哲 <juzhe.zhong@rivai.ai> writes:
> Thanks Richard.
> I am planning to seperate a patch with only creat_iv stuff only.
>
> Are you suggesting that I remove "tree_code incr_op = code;"
> Use the argument directly ?
>
> I saw the codes here:
>
>   /* For easier readability of the created code, produce MINUS_EXPRs
>      when suitable.  */
>   if (TREE_CODE (step) == INTEGER_CST)
>     {
>       if (TYPE_UNSIGNED (TREE_TYPE (step)))
> {
>   step1 = fold_build1 (NEGATE_EXPR, TREE_TYPE (step), step);
>   if (tree_int_cst_lt (step1, step))
>     {
>       incr_op = MINUS_EXPR;
>       step = step1;
>     }
> }
>       else
> {
>   bool ovf;
>
>   if (!tree_expr_nonnegative_warnv_p (step, &ovf)
>       && may_negate_without_overflow_p (step))
>     {
>       incr_op = MINUS_EXPR;
>       step = fold_build1 (NEGATE_EXPR, TREE_TYPE (step), step);
>     }
> }
>     }
>   if (POINTER_TYPE_P (TREE_TYPE (base)))
>     {
>       if (TREE_CODE (base) == ADDR_EXPR)
> mark_addressable (TREE_OPERAND (base, 0));
>       step = convert_to_ptrofftype (step);
>       if (incr_op == MINUS_EXPR)
> step = fold_build1 (NEGATE_EXPR, TREE_TYPE (step), step);
>       incr_op = POINTER_PLUS_EXPR;
>     }
>   /* Gimplify the step if necessary.  We put the computations in front of the
>      loop (i.e. the step should be loop invariant).  */
>   step = force_gimple_operand (step, &stmts, true, NULL_TREE);
>   if (stmts)
>     gsi_insert_seq_on_edge_immediate (pe, stmts);
>
>   stmt = gimple_build_assign (va, incr_op, vb, step);
> ...
>
> It seems that it has complicated conditions here to change value of variable "incr_op".
> That's why I define a temporary variable "tree_code incr_op = code;" here and
> let the following codes change the value of "incr_op".
>
> Could you give me some hints of dealing with this piece of code to get rid of "tree_code incr_op = code;" ?

Yeah, but like I said in the review, those later:
 
      incr_op = MINUS_EXPR;
 
stmts need to be updated to something that flips between PLUS_EXPR
and MINUS_EXPR (with updates to the comments).  Just leaving them
as-is is incorrect (in cases where the caller passed MINUS_EXPR
rather than PLUS_EXPR).

The POINTER_PLUS_EXPR handling is fine due to the conditional
negate beforehand.

Thanks,
Richard