On Thu, 20 Dec 2012, Steven Bosscher wrote:
> On Thu, Dec 20, 2012 at 1:43 PM, Richard Biener wrote:
> > --- 724,746 ----
> >
> > cfg_hooks->merge_blocks (a, b);
> >
> > if (current_loops != NULL)
> > {
> > ! /* If the block we merge into is a loop header do nothing unless
> > ... */
> > ! if (a->loop_father->header == a)
> > ! {
> > ! /* ... we merge two loop headers, in which case we kill
> > ! the inner loop. */
>
> Before loops were maintained, we'd simply re-discover the nested
> loops. Do we now lose this information?
When we merge loop headers we effectively merge two loops (in this
case cross-jumping merged the latches and the headers). We re-discover
the nest when multiple latches remain and we disambiguate loops
with multiple latches.
> How about adjusting the can_merge_blocks hook to reject merging loop headers?
I didn't want to do that, but sure - that's another possibility. In
this case the outer loop is really unnecessary.
Richard.
