gcc11 O3 warnings

[tjhei]

I am getting the following 2 warnings with gcc 11.3 on Ubuntu 22.04:

/ssd/deal-git/source/grid/tria.cc: In static member function ‘static typename dealii::Triangulation<3, spacedim>::DistortedCellList dealii::internal::TriangulationImplementation::Implementation::execute_refinement_isotropic(dealii::Triangulation<3, spacedim>&, bool) [with int spacedim = 3]’:
/ssd/deal-git/source/grid/tria.cc:5712:43: warning: ‘void* __builtin_memcpy(void*, const void*, long unsigned int)’ writing 17179869180 bytes into a region of size 108 overflows the destination [-Wstringop-overflow=]
 5712 |                       vertex_indices[k++] = hex->vertex_index(i);
/ssd/deal-git/source/grid/tria.cc:5706:48: note: destination object ‘vertex_indices’ of size 108
 5706 |                   std::array<unsigned int, 27> vertex_indices = {};
      |                                                ^~~~~~~~~~~~~~
/ssd/deal-git/source/grid/tria.cc: In member function ‘void dealii::Triangulation<dim, spacedim>::execute_coarsening() [with int dim = 3; int spacedim = 3]’:
/ssd/deal-git/source/grid/tria.cc:14944:32: warning: iteration 12 invokes undefined behavior [-Waggressive-loop-optimizations]
14944 |               ++line_cell_count[line_indices[l]];
      |                 ~~~~~~~~~~~~~~~^
/ssd/deal-git/source/grid/tria.cc:14943:40: note: within this loop
14943 |             for (unsigned int l = 0; l < cell->n_lines(); ++l)
      |                                      ~~^~~~~~~~~~~~~~~~~

I played with the loops a little bit, but I am not able to get rid of the warnings. Any suggestions? Is the first one an unsigned int overflow?

[bangerth]

For reference, I have that too. I have to admit that I don't understand how the compiler comes up with this.

[bangerth]

Is this still true? I thought we fixed that.

[kronbichler]

Yes, we fixed this in #15220; that PR also gives an explanation on why this happened. I'm closing.