https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81366
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2017-07-10
CC| |jakub at gcc dot gnu.org
Ever confirmed|0 |1
--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
FRE or similar are unable to sufficiently optimize the mess added because of
the std::max references.
If one uses
m = x[i] < m ? m : x[i];
instead of
m = std::max(x[i], m);
in the loop, then before ifcvt we see:
_21 = GOMP_SIMD_LANE (simduid.1_12(D));
_1 = (long unsigned int) i_35;
_2 = _1 * 8;
_3 = x_22(D) + _2;
_4 = *_3;
_23 = D.2907[_21];
if (_4 < _23)
goto <bb 8>; [50.00%] [count: INV]
else
goto <bb 9>; [50.00%] [count: INV]
<bb 8> [42.50%] [count: INV]:
<bb 9> [85.00%] [count: INV]:
# iftmp.0_6 = PHI <_23(8), _4(7)>
D.2907[_21] = iftmp.0_6;
i_25 = i_35 + 1;
if (n_15(D) > i_25)
and that can be handled just fine.
But with std::max we have:
# i_38 = PHI <0(6), i_25(10)>
_20 = GOMP_SIMD_LANE (simduid.2_12(D));
_1 = (long unsigned int) i_38;
_2 = _1 * 8;
_3 = x_21(D) + _2;
_23 = MEM[(const double &)_3];
_28 = MEM[(const double &)&D.2904][_20];
if (_23 < _28)
goto <bb 8>; [50.00%] [count: INV]
else
goto <bb 9>; [50.00%] [count: INV]
<bb 8> [42.50%] [count: INV]:
_42 = (sizetype) _20;
_7 = _42 * 8;
_22 = &D.2904 + _7;
pretmp_50 = MEM[(const double &)_22];
<bb 9> [85.00%] [count: INV]:
# prephitmp_51 = PHI <_23(7), pretmp_50(8)>
D.2904[_20] = prephitmp_51;
i_25 = i_38 + 1;
if (n_14(D) > i_25)
It figured out that one of the prephitmp_51 arguments is _23, but not that
pretmp_50 = _28;
and thus it wants to generate a masked load.
