[Bug c/107754] New: Confusing -Warray-bounds warning with strcpy

[Bug c/107754] New: Confusing -Warray-bounds warning with strcpy

[nightstrike at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107754

            Bug ID: 107754
           Summary: Confusing -Warray-bounds warning with strcpy
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nightstrike at gmail dot com
  Target Milestone: ---

Metabug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=warray-bounds

// Compile with GCC 12.2.0 with -O2:
//    warning: ‘strcpy’ offset 0 is out of the bounds [0, 0] [-Warray-bounds]
// no warning without -O2

struct Inst;
struct Class { int offset; };

static struct Class * classFoo; // No problem without static here

struct Foo
{
   unsigned int a;   // no problem if commented out
   char bar[1024];
};

void setFoo(struct Inst * this, const char * value)
{
   struct Foo * ptr = (struct Foo *)(this ? (((char *)this) + classFoo->offset)
: 0);
   __builtin_strcpy(ptr->bar, value);
}


$ gcc-12 -c -O2 -Warray-bounds a.c -o /dev/null
a.c: In function 'setFoo':
a.c:19:4: warning: '__builtin_strcpy' offset 0 is out of the bounds [0, 0]
[-Warray-bounds]
   19 |    __builtin_strcpy(ptr->bar, value);
      |    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

[Bug tree-optimization/107754] Confusing -Warray-bounds warning with strcpy with a null pointer

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107754

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2022-11-18
     Ever confirmed|0                           |1
            Summary|Confusing -Warray-bounds    |Confusing -Warray-bounds
                   |warning with strcpy         |warning with strcpy with a
                   |                            |null pointer
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed. Note the warning message is correct; just confusing and does not
mention a null pointer here.

Reduced further:
struct Foo
{
   unsigned int a;
   char bar[1024];
};
void setFoo(const char * value)
{
   struct Foo * ptr = 0;
   __builtin_strcpy(ptr->bar, value);
}


---- CUT ---
Since the offset for the character array is non-zero, we see a non-zero
constant and (based on other settings) assume it is the null pointer page and
we get a size of 0 (which is ok) but don't mention a null pointer.

There might be other dups of this but I am not going to search for it right
now.

[Bug tree-optimization/107754] Confusing -Warray-bounds warning with strcpy with a null pointer and non-zero offset for struct array

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107754

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note in the origin "reduced" testcase, we had a conditional null pointer which
was exposing the null pointer at -O2 due to optimizations.