https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63168
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |ASSIGNED
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
It looks like do_while_loop_p is fooled by the CFG structure and hits
static bool
do_while_loop_p (struct loop *loop)
{
gimple stmt = last_stmt (loop->latch);
/* If the latch of the loop is not empty, it is not a do-while loop. */
if (stmt
&& gimple_code (stmt) != GIMPLE_LABEL)
return false;
the loop at CH time looks like
|
v
/-> <bb 5>
| exit test --->
| |
| <bb 3>
| ...
| |
\ <bb 4>
-- (empty but with a PHI)
phiopt introduces this singleton PHI:
<bb 3>:
max_8 = *it_6;
- if (max_8 > max_2)
- goto <bb 5>;
- else
- goto <bb 4>;
+ max_10 = MAX_EXPR <max_2, max_8>;
<bb 4>:
+ # max_9 = PHI <max_10(3)>
<bb 5>:
- # max_9 = PHI <max_2(4), max_8(3)>
-
- <bb 6>:
- # it_1 = PHI <it_6(5), it_4(D)(2)>
- # max_2 = PHI <max_9(5), max_5(2)>
+ # it_1 = PHI <it_6(4), it_4(D)(2)>
+ # max_2 = PHI <max_9(4), max_5(2)>
it looks like the CH predicate relies on copy-propagated form
(a latch block with an SSA name copy should also be considered empty IMHO).
I think that cfgcleanup should merge
<bb A>
....
| single-succ/pred
<bb B>
# var = PHI <arg>
and rewrite the PHIs to copies. Its comment even says so:
/* Merging the blocks may create new opportunities for folding
conditional branches (due to the elimination of single-valued PHI
nodes). */
if (single_succ_p (bb)
&& can_merge_blocks_p (bb, single_succ (bb)))
{
merge_blocks (bb, single_succ (bb));
return true;
}
Ah, but
/* Checks whether we can merge block B into block A. */
static bool
gimple_can_merge_blocks_p (basic_block a, basic_block b)
{
...
/* Protect the loop latches. */
if (current_loops && b->loop_father->latch == b)
return false;
triggers here (merge_blocks doesn't handle merging with a latch).
Mine.
