On Wed, 30 Jan 2013, Steven Bosscher wrote:
> On Wed, Jan 30, 2013 at 12:01 AM, Steven Bosscher wrote:
> > To prevent that mistake in the future, I've add an assert in dominance.c.
>
> Hmm, that worked with my release-checking compiler of course, but
> fails in at least tree-ssa-dom.c (same as for fwprop.c,
> loop_optimizer_init destroys fast queries) and tree-ssa-loop-im.c (not
> sure yet why).
>
> NB, the fwprop.c change is independent and should go in. The domwalk.c
> thing is something to maybe postpone to gcc 4.9.
The fwprop.c change is ok - fwprop.c doesn't seem to care about
identified latches or preheaders.
Now, I wonder what part of loop_optimizer_init wrecks dominance
info - I _suppose_ it's disambiguate_loops_with_multiple_latches (),
but that only ends up calling make_forwarder_block which looks like
it has code to fix dominators via iterate_fix_dominators ().
Hmm, it seems to be
make_forwarder_block (basic_block bb, bool (*redirect_edge_p) (edge),
void (*new_bb_cbk) (basic_block))
{
...
fallthru = split_block_after_labels (bb);
that sets DOM_NO_FAST_QUERY via add_to_dominance_info () via
create_basic_block. Then split_block () does
482 if (dom_info_available_p (CDI_DOMINATORS))
483 {
484 redirect_immediate_dominators (CDI_DOMINATORS, bb, new_bb);
485 set_immediate_dominator (CDI_DOMINATORS, new_bb, bb);
486 }
but that doesn't set dominance info to DOM_OK again. The
iterate_fix_dominators doesn't do that either.
IMHO at least split_block () should be able to preserve fast queries?
Thanks,
Richard.
> Testing this patch now:
>
> Index: domwalk.c
> ===================================================================
> --- domwalk.c (revision 195559)
> +++ domwalk.c (working copy)
> @@ -147,8 +147,17 @@ walk_dominator_tree (struct dom_walk_dat
> bitmap_clear (visited);
> bitmap_set_bit (visited, ENTRY_BLOCK_PTR->index);
>
> + /* Make sure dominance information is available, and compute fast queries
> + if necessary. */
> + gcc_assert (dom_info_state (walk_data->dom_direction) >=
> DOM_NO_FAST_QUERY);
> + calculate_dominance_info (walk_data->dom_direction);
> +
> while (true)
> {
> + /* Thou shall not modify the dominator tree while walking it
> + (nor present it without fast queries available). */
> + gcc_assert (dom_info_state (walk_data->dom_direction) == DOM_OK);
> +
> /* Don't worry about unreachable blocks. */
> if (EDGE_COUNT (bb->preds) > 0
> || bb == ENTRY_BLOCK_PTR
>
>
--
Richard Biener <[email protected]>
SUSE / SUSE Labs
SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746
GF: Jeff Hawn, Jennifer Guild, Felix Imend
