https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105832
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |NEW
Assignee|rguenth at gcc dot gnu.org |unassigned at gcc dot
gnu.org
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
So the difference boils down to GCC 12 ending up with
if (iftmp.0_9 == 1)
{
if (iftmp.1_10 != 0)
{
loop with call to foo ();
}
}
while the new unswitching code swaps these and ends up with
if (iftmp.1_10 != 0)
{
if (iftmp.0_9 == 1)
{
loop with call to foo ();
}
}
the old code also created one pointless unreachable loop copy. GCC 12
manages to elide the loop calling foo() in thread2 after fre5.
There's nothing wrong with unswitching here I think - we're at most unlucky
with the order of unswitchings (but that might change from current 'random'
to a cost based order).
