[Bug c++/105373] miscompile involving lambda coroutines and an object bitwise copied instead of via the copy constructor

["avi at scylladb dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105373

--- Comment #11 from Avi Kivity <avi at scylladb dot com> ---
Created attachment 52899
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52899&action=edit
simple(r) reproducer

I was able to reduce it to something simple (102 lines), but I was only able to
verify that wrong code is generated on the gimple level (where my understanding
is very limited). Still, to my inexperienced eyes it looks like an object with
a copy constructor is being copied bitwise.

Compile with (gcc 11.3.1)

    g++ -Wfatal-errors -w -std=gnu++20  -march=westmere -fvisibility=hidden  -c
-o table.o table.i -fdump-tree-gimple -g 

and observe in table.i.006t.gimple:

    struct lw_shared_ptr D.2740 [value-expr: frame_ptr->D.2740_4_5];

and then

    frame_ptr->D.2741_4_5.__old4 = frame_ptr->D.2740_4_5;


in other places, variables of the same type are copied using the copy
constructor.