https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85615
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |law at gcc dot gnu.org
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
It looks like loop structure is already broken to the extent that
loop->num_nodes
cannot be trusted and thus
bblocks = XCNEWVEC (basic_block, loop->num_nodes);
dbds_ce_stop = loop->header;
nblocks = dfs_enumerate_from (loop->latch, 1, dbds_continue_enumeration_p,
bblocks, loop->num_nodes, bb);
breaks (not enough space in bblocks, thus bb is not reachable from
loop->latch).
In fact loop structure looks totally broken to me :/
We seem to thread through always true/false conditions that are left over from
VRP substitute-and-fold which relies on CFG cleanup to cleanup things here.
When we thread through block 12,
Breakpoint 5, thread_block_1 (bb=<basic_block 0x7ffff689f750 (12)>,
noloop_only=true, joiners=false)
we have threaded through the loop header which in the end wrecks things.
We do not hit
/* One case occurs when there was loop header buried in a jump
threading path that crosses loop boundaries. We do not try
and thread this elsewhere, so just cancel the jump threading
request by clearing the AUX field now. */
if (bb->loop_father != e2->src->loop_father
&& !loop_exit_edge_p (e2->src->loop_father, e2))
{
nor
/* Another case occurs when trying to thread through our
own loop header, possibly from inside the loop. We will
thread these later. */
unsigned int i;
for (i = 1; i < path->length (); i++)
{
but the case involves a very long path (6 edges) where we thread through
the header of an outer loop into an inner loop and finally through the
exit of the inner loop. I guess we should hit the first case by allowing
the exit threading only if the exit is to bb->loop_father. Otherwise
we create an alternate entry (which is what happens here). Like by
making the check consisted with the others.
I'm testing the following.
Index: gcc/tree-ssa-threadupdate.c
===================================================================
--- gcc/tree-ssa-threadupdate.c (revision 259879)
+++ gcc/tree-ssa-threadupdate.c (working copy)
@@ -1309,7 +1309,7 @@ thread_block_1 (basic_block bb, bool nol
and thread this elsewhere, so just cancel the jump threading
request by clearing the AUX field now. */
if (bb->loop_father != e2->src->loop_father
- && !loop_exit_edge_p (e2->src->loop_father, e2))
+ && !loop_exit_edge_p (bb->loop_father, e2))
{
/* Since this case is not handled by our special code
to thread through a loop header, we must explicitly
