On Tue, Apr 18, 2017 at 12:46 PM, Bin Cheng <bin.ch...@arm.com> wrote:
> Hi,
> We generally need to compute cand step in loop preheader and use it in loop
> body.
> Unless it's an SSA_NAME of constant integer, an invariant expression is
> needed.
I'm confused as to what this patch does. Comments talk about "Handle step as"
but then we print "Depend on inv...". And we share bitmaps, well it seems
+ find_inv_vars (data, &step, &cand->inv_vars);
+
+ iv_inv_expr_ent *inv_expr = get_loop_invariant_expr (data, step);
+ /* Share bitmap between inv_vars and inv_exprs for cand. */
+ if (inv_expr != NULL)
+ {
+ cand->inv_exprs = cand->inv_vars;
+ cand->inv_vars = NULL;
+ if (cand->inv_exprs)
+ bitmap_clear (cand->inv_exprs);
+ else
+ cand->inv_exprs = BITMAP_ALLOC (NULL);
+
+ bitmap_set_bit (cand->inv_exprs, inv_expr->id);
just shares the bitmap allocation (and leaks cand->inv_exprs?).
Note that generally it might be cheaper to use bitmap_head instead of
bitmap in the various structures (and then bitmap_initialize ()), this
saves one indirection.
Anyway, the relation between inv_vars and inv_exprs is what confuses me.
Maybe it's the same as for cost_pair? invariants vs. loop invariants?
whatever that means...
That is, can you expand the comments in cost_pair / iv_cand for inv_vars
vs. inv_exprs, esp what "invariant" actually means?
Thanks,
Richard.
> Thanks,
> bin
>
> 2017-04-11 Bin Cheng <bin.ch...@arm.com>
>
> * tree-ssa-loop-ivopts.c (struct iv_cand): New field inv_exprs.
> (dump_cand): Support iv_cand.inv_exprs.
> (add_candidate_1): Record invariant exprs in iv_cand.inv_exprs
> for candidates.
> (iv_ca_set_no_cp, iv_ca_set_cp, free_loop_data): Support
> iv_cand.inv_exprs.
