https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96481
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |missed-optimization
Last reconfirmed| |2020-08-05
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
Blocks| |53947
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Yes, this is a known limitation in that for basic-block SLP we do not perform
if-conversion. Instead the basic-block SLP code sees
<bb 2> [local count: 1073741824]:
_1 = *pd_17(D);
_2 = *pc_19(D);
_3 = *pb_20(D);
_4 = *pa_21(D);
if (_3 < _4)
goto <bb 11>; [50.00%]
else
goto <bb 3>; [50.00%]
<bb 11> [local count: 536870912]:
goto <bb 4>; [100.00%]
<bb 3> [local count: 536870913]:
<bb 4> [local count: 1073741824]:
# iftmp.20_23 = PHI <_1(3), _2(11)>
*dst_22(D) = iftmp.20_23;
_5 = MEM[(const unsigned int *)pd_17(D) + 4B];
_6 = MEM[(const unsigned int *)pc_19(D) + 4B];
_7 = MEM[(const unsigned int *)pb_20(D) + 4B];
_8 = MEM[(const unsigned int *)pa_21(D) + 4B];
...
which also rips apart the memory groups (we're slowly relaxing another
limitation that the basic-block SLP code operates on a single basic-block
at a time but for data refs this restriction will prevail).
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53947
[Bug 53947] [meta-bug] vectorizer missed-optimizations
