[Bug c++/86210] New: [6/7/8/9 Regression] Missing -Wnonnull warning for function defined in the same TU

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86210

            Bug ID: 86210
           Summary: [6/7/8/9 Regression] Missing -Wnonnull warning for
                    function defined in the same TU
           Product: gcc
           Version: 8.1.1
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

void * declared_not_defined(void * p) __attribute__((nonnull));

inline void * declared_and_defined(void * p) __attribute__((nonnull));

int main()
{
    int * const p = 0;
    declared_not_defined(p);
    declared_and_defined(p);
}

void * declared_and_defined(void * p) { return p; }


G++ 5 and 6 fail to give any warnings at all, at any optimisation level.

G++ 7 and 8 and trunk only warn at -O1 and higher, and only for one of the two
calls:

x.cc: In function ‘int main()’:
x.cc:8:25: warning: argument 1 null where non-null expected [-Wnonnull]
     declared_not_defined(p);
     ~~~~~~~~~~~~~~~~~~~~^~~
x.cc:1:8: note: in a call to function ‘void* declared_not_defined(void*)’
declared here
 void * declared_not_defined(void * p) __attribute__((nonnull));
        ^~~~~~~~~~~~~~~~~~~~


G++ 4.7, 4.8 and 4.9 warns about both calls, without any optimisation:

x.cc: In function ‘int main()’:
x.cc:8:27: warning: null argument where non-null required (argument 1)
[-Wnonnull]
     declared_not_defined(p);
                           ^
x.cc:9:27: warning: null argument where non-null required (argument 1)
[-Wnonnull]
     declared_and_defined(p);
                           ^


Compiling it as C gives almost the opposite results! I get no warnings for any
release before 7.1, and a warning for only one function with 7.1 but only with
optimisation, and warnings for both function for 8.1 with optimisation. So for
C thigns have been getting gradually better, but worse for C++.