https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101150
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Target Milestone|--- |11.2
Status|UNCONFIRMED |NEW
Keywords| |missed-optimization
Component|c++ |tree-optimization
Last reconfirmed| |2021-06-22
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
There seems to be some missing optimizations (jump threading) here.
First one:
long int _12;
_12 = _9 - _15;
if (_12 != 0)
goto <bb 4>; [33.00%]
else
goto <bb 3>; [67.00%] // this should just jump to bb 15 because _12 == 0
and there for _9 == _15
<bb 3> [local count: 79134772]:
if (_9 != _15) /// This should always be false coming from bb 2 because _12
== 0 there for _9 == _15
goto <bb 11>; [89.00%]
else
goto <bb 15>; [11.00%]
...
<bb 11> [local count: 104641928]:
# _143 = PHI <_18(8), _9(3)>
# _118 = PHI <_19(8), _15(3)>
# v$_M_start_84 = PHI <_104(8), 0B(3)>
# prephitmp_123 = PHI <_12(8), _12(3)>
_133 = (unsigned long) _143;
_110 = (unsigned long) _118;
_125 = _133 - _110;
....
<bb 15> [local count: 117575200]:
return;
Second one:
...
<bb 4> [local count: 19488414]:
_64 = (long unsigned int) _12;
if (_64 > 9223372036854775804)
goto <bb 5>; [0.04%]
else
goto <bb 6>; [99.96%]
....
<bb 6> [local count: 9740309]:
if (_12 != 0) // This should always be true as _12 should always != 0 on
coming into this bb because we can only come via the if statement in bb 4 on
the true edge of the conditional.
goto <bb 7>; [100.00%]
else
goto <bb 16>; [0.00%] /// NOTE BB 16 is where the null pointer write it
located
--------- CUT -------
The reason why if you have both foo and bar defined, there is a heuristics of
the inlining of vector::_M_default_append which causes the difference, nothing
shocking really.
