[Bug testsuite/83869] [8 regression] c-c++-common/attr-nonstring-3.c fails starting with r256683

["msebor at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83869

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
         Depends on|                            |82609

--- Comment #2 from Martin Sebor <msebor at gcc dot gnu.org> ---
The failing test cases are these two:

$ cat -n gcc/testsuite/c-c++-common/attr-nonstring-3.c | grep
"[[:space:]]25[07][[:space:]]"
   250    T (stpncpy (arr, str, N + 1));          /* { dg-warning "writing 5
bytes into a region of size 4 overflows " } */
   257    T (stpncpy (p->arr, p->str, N + 1));    /* { dg-warning "writing 5
bytes into a region of size 4 overflows" } */

The following test case demonstrates the problem.  The root cause is bug 82609:
the extra set of parentheses around the stpncpy call suppresses the middle-end
warnings in C++ (C is unaffected).

$ cat pr83869.C && gcc -O2 -S -Wstringop-overflow pr83869.C
#include <string.h>

char a[4], b[4];

void sink (char*);

void warn_overflow (void)
{
  sink (stpncpy (a, b, sizeof a + 1));   // -Wstringop-overflow (good)
}

void bug_82609_missing_warn_overflow (void)
{
  sink ((stpncpy (a, b, sizeof a + 1)));   // missing -Wstringop-overflow
}
pr83869.C: In function ‘void warn_overflow()’:
pr83869.C:9:8: warning: ‘char* stpncpy(char*, const char*, size_t)’ writing 5
bytes into a region of size 4 overflows the destination [-Wstringop-overflow=]
   sink (stpncpy (a, b, sizeof a + 1));   // -Wstringop-overflow (good)
   ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82609
[Bug 82609] missing -Warrray-bounds on an argument in parentheses