https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107690
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |12.3
Summary|Regression in |[12/13 Regression]
|ranges::transform |vectorization fails for
|vectorization |std::ranges::transform due
| |to IR changes
Last reconfirmed| |2022-11-14
Blocks| |53947
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
Keywords| |missed-optimization,
| |needs-bisection
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
In GCC 12 before the vectorizer we have:
<bb 2> [local count: 114863530]:
_4 = v_2(D) + 64;
_5 = &v_2(D)->_M_elems;
if (_4 != _5)
goto <bb 5>; [89.30%]
else
goto <bb 4>; [10.70%]
<bb 5> [local count: 102576004]:
<bb 3> [local count: 958878296]:
# __first1_24 = PHI <_11(6), &u._M_elems(5)>
# __first2_25 = PHI <_12(6), _5(5)>
_7 = MEM[(const int &)__first1_24];
_9 = *__first2_25;
_10 = _7 + _9;
*__first1_24 = _10;
_11 = __first1_24 + 4;
_12 = __first2_25 + 4;
_15 = _4 != _12;
_18 = &MEM <struct array> [(void *)&u + 64B] != _11;
_16 = _15 & _18;
if (_16 != 0)
goto <bb 6>; [89.30%]
else
goto <bb 4>; [10.70%]
<bb 6> [local count: 856302294]:
goto <bb 3>; [100.00%]
But with GCC 11 we had:
<bb 2> [local count: 114863530]:
_2 = &MEM <const int[16]> [(void *)v_3(D) + 64B];
_5 = &v_3(D)->_M_elems;
goto <bb 5>; [100.00%]
<bb 4> [local count: 114863532]:
<retval> = u;
return <retval>;
<bb 6> [local count: 899822495]:
<bb 5> [local count: 1014686026]:
# __first1_22 = PHI <_11(6), &u._M_elems(2)>
# __first2_23 = PHI <_12(6), _5(2)>
# ivtmp_24 = PHI <ivtmp_13(6), 16(2)>
_7 = MEM[(const int &)__first1_22];
_9 = *__first2_23;
_10 = _7 + _9;
*__first1_22 = _10;
_11 = __first1_22 + 4;
_12 = __first2_23 + 4;
ivtmp_13 = ivtmp_24 - 1;
if (ivtmp_13 != 0)
goto <bb 6>; [93.84%]
else
goto <bb 4>; [6.16%]
There is a missing optimization before the vectorizer which is causing the
vectorizer not to know how many iterations the loop is for.
I am tries tracking down which passes the IR changes to make things worse but I
didn't do a good at doing that.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53947
[Bug 53947] [meta-bug] vectorizer missed-optimizations
