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[Bug libstdc++/85116] std::min_element does not optimize well with inlined predicate
- From: "rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Thu, 26 Apr 2018 12:31:58 +0000
- Subject: [Bug libstdc++/85116] std::min_element does not optimize well with inlined predicate
- Auto-submitted: auto-generated
- References: <bug-85116-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85116
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
So loop-header copying now DTRT but then PRE is faced with
<bb 4> [local count: 955630223]:
# __first_20 = PHI <&testArray._M_elems(2), __first_21(7)>
# __first_21 = PHI <&MEM[(void *)&testArray + 8B](2), __first_7(7)>
# __result_22 = PHI <&testArray._M_elems(2), __result_15(7)>
_8 = MEM[(const double *)__first_20 + 8B];
_10 = *__result_22;
_11 = _8 - offset_2(D);
_12 = ABS_EXPR <_11>;
_13 = _10 - offset_2(D);
_14 = ABS_EXPR <_13>;
if (_12 < _14)
goto <bb 5>; [50.00%]
else
goto <bb 8>; [50.00%]
<bb 5> [local count: 477815111]:
goto <bb 3>; [100.00%]
<bb 8> [local count: 477815112]:
<bb 3> [local count: 955630224]:
# __result_15 = PHI <__first_21(5), __result_22(8)>
__first_7 = __first_21 + 8;
if (__first_7 != &MEM[(void *)&testArray + 8000B])
goto <bb 7>; [89.00%]
else
goto <bb 6>; [11.00%]
<bb 7> [local count: 850510900]:
goto <bb 4>;
where the situation is too confusing to be recognized. As said, loop-header
copying doing a SSA update introduces the extra IV somehow. That needs to be
investigated.