[Bug analyzer/105103] New: RFE: detect bogus use of varargs in analyzer

[dmalcolm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105103

            Bug ID: 105103
           Summary: RFE: detect bogus use of varargs in analyzer
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: analyzer
          Assignee: dmalcolm at gcc dot gnu.org
          Reporter: dmalcolm at gcc dot gnu.org
  Target Milestone: ---

The analyzer doesn't yet have any handling for the types, macros, functions
from <stdarg.h>:

https://en.cppreference.com/w/c/variadic
https://www.man7.org/linux/man-pages/man3/stdarg.3.html

It would be nice to e.g. detect the various undefined behaviors listed in the
above e.g. 

"If ap is passed to a function that uses va_arg(ap,type), then the value of ap
is undefined after the return of that function."

etc.

We could also implement __builtin_va_start, __builtin_va_end, etc
and have region_model unpack variadic args in interprocedural calls,
effectively inlining the analysis.