[Bug c++/78841] [6 regression] optimizer bug (silent bad codegen)

[Casey at Carter dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78841

--- Comment #2 from Casey Carter <Casey at Carter dot net> ---
Created attachment 40371
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40371&action=edit
compressed preprocessed repro