https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113134
--- Comment #8 from JuzheZhong <juzhe.zhong at rivai dot ai> ---
(In reply to Tamar Christina from comment #7)
> You may be able to use the same approach as
>
> else if (LOOP_VINFO_FULLY_MASKED_P (loop_vinfo))
>
> that is, reverse both the mask and the vector and using extract last.
> It's not going to be performance critical so it's more important to be
> correct rather than fast.
I just carefully read this code:
/* For an inverted control flow with early breaks we want EXTRACT_FIRST
instead of EXTRACT_LAST. Emulate by reversing the vector and mask. */
if (restart_loop && LOOP_VINFO_EARLY_BREAKS (loop_vinfo))
{
/* First create the permuted mask. */
tree perm_mask = perm_mask_for_reverse (TREE_TYPE (mask));
tree perm_dest = copy_ssa_name (mask);
gimple *perm_stmt
= gimple_build_assign (perm_dest, VEC_PERM_EXPR, mask,
mask, perm_mask);
vect_finish_stmt_generation (loop_vinfo, stmt_info, perm_stmt,
&gsi);
mask = perm_dest;
/* Then permute the vector contents. */
tree perm_elem = perm_mask_for_reverse (vectype);
perm_dest = copy_ssa_name (vec_lhs_phi);
perm_stmt
= gimple_build_assign (perm_dest, VEC_PERM_EXPR, vec_lhs_phi,
vec_lhs_phi, perm_elem);
vect_finish_stmt_generation (loop_vinfo, stmt_info, perm_stmt,
&gsi);
vec_lhs_phi = perm_dest;
}
Suppose the loop mask is generated by whilelo instruction of ARM SVE.
Suppose we have 8 elements in a single whole vector.
mask = whilo (0, res) if res = 6, then mask = 11111000.
data = 12345678
Then if it is early break. You are reversing both data and mask as follows:
new_mask = 00011111
new_data = 87654321
Then use the EXTRACT_LAST, we will get value = 1 for early break.
Am I right ?
