[Bug other/77421] Bugs found in GCC with the help of PVS-Studio

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77421

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Created attachment 39525
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=39525&action=edit
Patch to fix most of the reported issues.

I've created three new bugs for cases where the fix isn't clear. This patch
addresses the more obvious fixes.