On Wed, Dec 02, 2015 at 06:21:47PM +0000, Segher Boessenkool wrote:
> --- a/gcc/shrink-wrap.c
> +++ b/gcc/shrink-wrap.c
> @@ -752,7 +752,11 @@ try_shrink_wrapping (edge *entry_edge, bitmap_head
> *bb_with,
>
> /* If we can move PRO back without having to duplicate more blocks, do so.
> We can move back to a block PRE if every path from PRE will eventually
> - need a prologue, that is, PRO is a post-dominator of PRE. */
> + need a prologue, that is, PRO is a post-dominator of PRE. We might
> + need to duplicate PRE if there is any path from a successor of PRE back
> + to PRE, so don't allow that either (but self-loops are fine, as are any
> + other loops entirely dominated by PRE; this in general seems too
> + expensive to check for, for such an uncommon case). */
So, what will happen if PRE self-loops? It would be nice to have it covered
by a testcase.
> + bool ok = true;
> +
> + if (!can_get_prologue (pre, prologue_clobbered))
> + ok = false;
> +
> + FOR_EACH_EDGE (e, ei, pre->succs)
> + if (e->dest != pre
> + && dominated_by_p (CDI_POST_DOMINATORS, e->dest, pre))
> + ok = false;
I wonder if it wouldn't be better to:
if (!can_get_prologue (pre, prologue_clobbered))
ok = false;
else
FOR_EACH_EDGE (e, ei, pre->succs)
if (e->dest != pre
&& dominated_by_p (CDI_POST_DOMINATORS, e->dest, pre))
{
ok = false;
break;
}
so that it doesn't walk or continue walking the edges if not needed.
Anyway, that are my comments, I'll defer the rest of the review to somebody
else.
Jakub
