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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/94727] [10 Regression] GCC produces incorrect
 code with -O3 since r10-5071-g02d895504cc59be0
Date: Thu, 23 Apr 2020 06:44:35 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94727

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|                            |x86_64-*-*

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
test() is basic-block vectorized on the c-loop body which has the d- and
e-loops
completely unrolled.  We create some weird

  mask__84.17_18 =3D vect_cst__94 < vect_cst__20;
  vect_patt_266.18_6 =3D VEC_COND_EXPR <mask__84.17_18, vect_cst__16,
vect_cst__15>;

where vect_cst__94 and vect_cst__20 look like

 { var_3.1_42 ? -1 : 0, var_3.1_42 ? -1 : 0, ...

or even

 { _272 ? -1 : 0, ...

with

 _272 =3D _271 < var_11.0_40

so the vectorization is quite imperfect, mainly due to

t1.C:9:32: note:   =3D=3D> examining statement: _85 =3D var_11.0_40 > _86;
t1.C:12:69: missed:   not vectorized: relevant stmt not supported: _85 =3D
var_11.0_40 > _86;
t1.C:9:32: note:   Building vector operands from scalars instead

that doesn't yet explain what goes wrong here.=