STRING_CST nodes with embedded nuls are formatted in Gimple dumps only up to the first nul.  Characters beyond the first nul are not printed.  This makes the dumps incomplete (and raises the question of whether the code is even correct.)  This has recently been exacerbated by transforming braced-list initialized constant character arrays into STRING_CSTs (r263511).

$ cat f.c && gcc  -O2 -S -Wall -fdump-tree-gimple=/dev/stdout f.c
void f (char *d)
{
  const char a[3] = "\000ab";

  __builtin_strcpy (d, a);
}

void g (char *d)
{
  const char a[] = { 0, 'a', 'b', 'b' };

  __builtin_strcpy (d, a);
}
f (char * d)
{
  const char a[3];

  try
    {
      a = "";
      __builtin_strcpy (d, &a);
    }
  finally
    {
      a = {CLOBBER};
    }
}


g (char * d)
{
  const char a[4];

  try
    {
      a = "";
      __builtin_strcpy (d, &a);
    }
  finally
    {
      a = {CLOBBER};
    }
}