[Bug middle-end/79275] New: -Wformat-overflow false positive exceeding INT_MAX in glibc sysdeps/posix/tempname.c

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79275

            Bug ID: 79275
           Summary: -Wformat-overflow false positive exceeding INT_MAX in
                    glibc sysdeps/posix/tempname.c
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

As reported on libc-alpha
(https://sourceware.org/ml/libc-alpha/2017-01/msg00541.html) the following test
case triggers a false positive -Wformat-overflow warning:

$ cat a.c && gcc -O2 -S -Wall -m32 a.c
typedef __SIZE_TYPE__ size_t;

void f (char *dst, size_t n, const char *s)
{
  if (n < 2 || __INT_MAX__ - 2 < n)
    n = 2;

  __builtin_sprintf (dst, "%.*s %.*s", (int)n, s, (int)n, s);
}
a.c: In function ‘f’:
a.c:8:33: warning: ‘%.*s’ directive output between 0 and 2147483645 bytes may
cause result to exceed ‘INT_MAX’ [-Wformat-overflow=]
   __builtin_sprintf (dst, "%.*s %.*s", (int)n, s, (int)n, s);
                                 ^~~~