[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 #4 from Fritz Reese <foreese at gcc dot gnu.org> ---
Created attachment 46651
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=46651&action=edit
intermediate code for test case 2

You can see the central loop described in the original report from lines 18-25.
The bounds of the loop are problematic, as iterations 509-511 will overflow the
source buffer. The optimized version is able to detect the overflow and issue a
warning.