[Bug c/96740] New: frexp, modf, and remquo missing attribute nonnull

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96740

            Bug ID: 96740
           Summary: frexp, modf, and remquo missing attribute nonnull
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

The math built-in functions frexp, modf, and remquo take pointers to objects
that they are specified to unconditionally store a component of the result in. 
Their internal declarations should make use of attribute nonnull to trigger
-Wnonnull warnings when they're passed a null pointer.

$ cat z.c && gcc -O2 -S -Wall z.c
double f0 (double x)
{
  return __builtin_frexp (x, (int*)0);       // missing warning
}

double f1 (double x)
{ 
  return __builtin_modf (x, (double*)0);     // missing warning
}

double f2 (void)
{ 
  return __builtin_nan ((char*)0);           // -Wnonnull (good)
}

double f3 (double x, double y)
{ 
  return __builtin_remquo (x, y, (int*)0);   // missing warning
}

z.c: In function ‘f2’:
z.c:13:10: warning: argument 1 null where non-null expected [-Wnonnull]
   13 |   return __builtin_nan ((char*)0);           // -Wnonnull (good)
      |          ^~~~~~~~~~~~~
<built-in>: note: in a call to function ‘__builtin_nan’ declared ‘nonnull’