[Bug tree-optimization/88441] New: missing warning on a buffer overflow with non-constant offset and constant size

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88441

            Bug ID: 88441
           Summary: missing warning on a buffer overflow with non-constant
                    offset and constant size
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

The calls to memcpy in both functions either very likely or certainly overflow
the destination yet they are not diagnosed.  At least in the simple cases when
the size of the destination (or source) object is known sufficiently early,
before the calls are transformed to MEM_REF, the overflow could be diagnosed.

$ cat x.c && gcc -O2 -S -Wall -fdump-tree-gimple=/dev/stdout x.c
char a[8];

void f (int i, const void *p)
{
  // overflow very likely
  __builtin_memcpy (a + i, p, sizeof a);   // missing -Wstringop-overflow
}

void g (unsigned i, const void *p)
{
  // overflow certain
  if (i)
    __builtin_memcpy (a + i, p, sizeof a);   // missing -Wstringop-overflow
}
f (int i, const void * p)
{
  _1 = (sizetype) i;
  _2 = &a + _1;
  __builtin_memcpy (_2, p, 8);
}


g (unsigned int i, const void * p)
{
  if (i != 0) goto <D.1916>; else goto <D.1917>;
  <D.1916>:
  _1 = (sizetype) i;
  _2 = &a + _1;
  __builtin_memcpy (_2, p, 8);
  <D.1917>:
}