https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87074
--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
outer->header is:
bb_4 (preds = {bb_3 bb_11 }, succs = {bb_5 })
{
<bb 4> [local count: 118111601]:
# f.10_31 = PHI <f.10_27(3), _12(11)>
# .MEM_34 = PHI <.MEM_18(D)(3), .MEM_21(11)>
# g_lsm.15_33 = PHI <g_lsm.15_13(3), _9(11)>
_75 = (unsigned int) g_lsm.15_33;
}
the bb into which the inner loop exits is:
bb_6 (preds = {bb_5 }, succs = {bb_11 bb_7 })
{
<bb 6> [local count: 118111601]:
# _11 = PHI <_8(5)>
_9 = (int) _11;
_12 = f.10_31 + 1;
if (_12 <= 10)
goto <bb 11>; [89.00%]
else
goto <bb 7>; [11.00%]
}
and outer->latch is:
bb_11 (preds = {bb_6 }, succs = {bb_4 })
{
<bb 11> [local count: 105119325]:
goto <bb 4>; [100.00%]
}
>From what I can see, gimple-loop-jam.c verifies using bb_prevents_fusion_p
these 3 bbs, but nothing checks the outer loop's IVs.
The problem is that a value computed by the inner loop (_8) is then used inside
of the outer loop and fed into the next inner loop too.
So, shall we punt if there are any phis in single_exit (loop)->dest (other than
virtual) (assuming here that we are in loop closed SSA form) and thus there are
any SSA_NAME uses from the inner loop to next outer loop's iteration?
Or are there perhaps any exceptions that can be handled, like if a value
computed by the inner loop is not used only after the outer loop exits?
