https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99997
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Component|c |tree-optimization
Last reconfirmed| |2021-04-12
Keywords| |missed-optimization
Status|UNCONFIRMED |ASSIGNED
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
We expand from
_10 = (_Bool) _9;
if (_10 != 0)
goto <bb 4>; [50.00%]
else
goto <bb 3>; [50.00%]
;; succ: 4
;; 3
;; basic block 3, loop depth 0
;; pred: 2
_3 = page_2(D)->compound_head;
_4 = (_Bool) _3;
_11 = (int) _4;
;; succ: 4
;; basic block 4, loop depth 0
;; pred: 2
;; 3
# iftmp.0_5 = PHI <1(2), _11(3)>
_6 = (_Bool) iftmp.0_5;
return _6;
and what's obvious to see is that there are excessive conversions on 3->4.
There's the opportunity to constant fold the _6 = (_Bool) iftmp.0_5 conversion
on 2->4 by adjusting the type of iftmp.0_5 pushing another required conversion
on the 3->4 edge which should nicely combine with the conversions already
present there. At -O2 PRE performs this, at -O1 the same issue is present.
Note the & 1 truncations are inserted by RTL expansion and since we lack
partial DCE / sink on RTL it doesn't get optimized.
I'll look into the GIMPLE simplification.
