Thank you so much.
Can you take a look at this patch:
https://gcc.gnu.org/pipermail/gcc-patches/2023-May/618110.html
Thanks.
juzhe.zh...@rivai.ai
From: Richard Sandiford
Date: 2023-05-11 12:50
To: 钟居哲
CC: gcc-patches; rguenther
Subject: Re: [PATCH V4] VECT: Add decrement IV iteration loop control by
variable amount support
钟居哲 <juzhe.zh...@rivai.ai> writes:
> I am sorry that I am still confused about that.
>
> Is this what you want ?
>
> bool use_minus_p = TREE_CODE (step) == INTEGER_CST && ((TYPE_UNSIGNED
> (TREE_TYPE (step)) && tree_int_cst_lt (step1, step))
> || (!TYPE_UNSIGNED (TREE_TYPE (step)) &&
> !tree_expr_nonnegative_warnv_p (step, &ovf) && may_negate_without_overflow_p
> (step)));
>
> /* 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; /* Remove it. */
> step = step1;
> }
> }
> else
> {
> bool ovf;
>
> if (!tree_expr_nonnegative_warnv_p (step, &ovf)
> && may_negate_without_overflow_p (step))
> {
> incr_op = MINUS_EXPR; /* Remove it. */
> 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) /* Change it into if (use_minus_p) */
> step = fold_build1 (NEGATE_EXPR, TREE_TYPE (step), step);
> incr_op = POINTER_PLUS_EXPR; /* Remove it. */
> }
> /* 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);
>
> if (POINTER_TYPE_P (TREE_TYPE (base)))
> stmt = gimple_build_assign (va, POINTER_PLUS_EXPR, vb, step);
> else if (use_minus_p)
> stmt = gimple_build_assign (va, MINUS_EXPR, vb, step);
> else
> stmt = gimple_build_assign (va, incr_op, vb, step);
> ...
>
> Since I have no idea to make stmts flips between PLUS_EXPR and MINUS_EXPR.
No, I meant:
- Rename the "code" argument to "incr_op".
- Remove "tree_code incr_op = code;".
- Replace both instances of:
incr_op = MINUS_EXPR;
with:
incr_op = (incr_op == PLUS_EXPR ? MINUS_EXPR : PLUS_EXPR);
The point is that the current code (rightly) assumes that incr_op
always starts out as PLUS_EXPR, i.e. that STEP starts out applying
positively. Making STEP apply in the opposite direction is then as
simple as changing incr_op to MINUS_EXPR. But the new interface
allows STEP to start out applying positively or negatively, and so
this code needs to cope with both cases.
Thanks,
Richard
