[Bug fortran/91310] Read overflow generated by character array assignment to self

[foreese at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91310

--- Comment #3 from Fritz Reese <foreese at gcc dot gnu.org> ---
Created attachment 46650
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=46650&action=edit
intermediate code for test case 1

You can see the central condition described in the original report from lines
17-25, and the problematic __builtin_memmove on line 24, which in the optimized
version of the tree causes the warning.

> __builtin_memmove ((void *) &str, (void *) &str[D.3853]{lb: 1 sz: 1}, 512);