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From: "roystgnr at ices dot utexas.edu" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/100366] [11/12 Regression] spurious warning -
 std::vector::clear followed by std::vector::insert(vec.end(),
 ...) with -O2
Date: Mon, 06 Dec 2021 16:45:16 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100366

Roy Stogner <roystgnr at ices dot utexas.edu> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |roystgnr at ices dot utexa=
s.edu

--- Comment #11 from Roy Stogner <roystgnr at ices dot utexas.edu> ---
This can even be triggered via std::vector::operator=3D, at least in gcc 11=
.2.

My own code is slightly more involved than this, but I can boil it down to:

  std::vector<int> src(2,1), dest(2);
  dest =3D src;

and that's enough to trigger this warning in a -O2 -Wall -Werror build.

Oddly, if I write dest(2,0) rather than dest(2), I don't see any warning.=20
That's a fine workaround for my own non-performance-critical code path, but=
 I
wonder if it also indicates that the underlying optimization is no longer b=
eing
enabled here for code that would benefit.=