[Bug tree-optimization/92131] [8/9/10 Regression] incorrect assumption that (ao >= 0) is always false

[ebotcazou at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92131

--- Comment #19 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
Created attachment 47084
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=47084&action=edit
Tentative fix