https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115256
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed on Zen3 btw, fails with the test input already. Note that this may
still be a latent issue in 502.gcc_r. -funroll-loops isn't neccessary,
-O3 -flto was enough to reproduce (no specific sub-architecture required).
-fno-strict-aliasing avoids the issue.
--param dse-max-object-size=0 doesn't help (turn off live byte tracking)
The patch itself likely adds quite some extra DSE so that's too much to
track down. DSE doesn't have a debug counter at the moment,
but "bisecting" --param dse-max-alias-queries-per-store shows the issue
still happens with 64 but not with 48.
The issue still reproduces with -flto-partition=1to1 (if one wants to
try per-TU compile flags) and with -flto-partition=one (if you want to
add a debug counter and bisect the bad store, but =one is slow).
We ICE in cfgloopmanip.c:create_preheader here:
basic_block
create_preheader (struct loop *loop, int flags)
{
edge e, fallthru;
basic_block dummy;
int nentry = 0;
bool irred = false;
bool latch_edge_was_fallthru;
edge one_succ_pred = NULL, single_entry = NULL;
edge_iterator ei;
FOR_EACH_EDGE (e, ei, loop->header->preds)
{
if (e->src == loop->latch)
continue;
irred |= (e->flags & EDGE_IRREDUCIBLE_LOOP) != 0;
nentry++;
single_entry = e;
if (single_succ_p (e->src))
one_succ_pred = e;
}
gcc_assert (nentry);
^^^
placing noinline on the above function still reproduces the issue. We
seem to run the above for the loop tree root but call from create_preheaders
which does
1425 FOR_EACH_LOOP (li, loop, 0)
1426 create_preheader (loop, flags);
(note absence of LI_INCLUDE_ROOT) so somehow the loop iterator setup
is broken.
