[Bug tree-optimization/100366] [11/12 Regression] spurious warning - std::vector::clear followed by std::vector::insert(vec.end(), ...) with -O2

["roystgnr at ices dot utexas.edu" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100366

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

           What    |Removed                     |Added
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                 CC|                            |roystgnr at ices dot utexas.edu

--- Comment #11 from Roy Stogner <roystgnr at ices dot utexas.edu> ---
This can even be triggered via std::vector::operator=, 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 = 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. 
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 being
enabled here for code that would benefit.