https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92666
--- Comment #2 from Martin Sebor <msebor at gcc dot gnu.org> --- The check_function_restrict() function is called to do the -Wrestrict checking. It's called conditionally, from check_function_arguments(), when warn_restrict is nonzero. When called, the function calls fold_for_warn() for all arguments of the functions it checks for aliasing violations. fold_for_warn() ends up calling mark_rvalue_use() which ultimately calls mark_exp_read() which sets DECL_READ_P (exp) = 1 for VAR_DECL and PARM_DECL. None of this happens when -Wno-restrict is set.
