Scev analysing number of loop iterations returns (2^32-1) instead of -1

[Tobias Grosser]

I try to analyse this code:
------------------------------------------------------
int foo (int N)
{
  int ftab[257];
  int i, j;

  for (i = 0; i < N  - 7488645; i++)
    j = ftab [i];

  return j;
}
------------------------------------------------------

The number of iterations I get is:

(unsigned int) N_5(D) + 0x0ffffffff

However I expect it to be

(unsigned int) N_5(D) + (-1)

At the moment we convert these values in Graphite using int_cst_value
even if 0x0ffffffff does not fit in host_integerp(). In some cases we
get free wrapping to -1 (that seems to be correct), however in others
this hackish use of int_cst_value leads to incorrect code.

Now I try to convert this value directly to a gmp value. Using this
approach.

----------------------------------------------------------------------
double_int di = tree_to_double_int (t);
mpz_set_double_int (res, di, TYPE_UNSIGNED (TREE_TYPE (t)));
----------------------------------------------------------------------


However the "di" value is again (2^32 -1) instead of -1, so the gmp
value I get is not the -1 it actually should be.
The conversion from tree to gmp value seems to be correct as

double_int_negative_p (di) == false, as well as 
TYPE_UNSIGNED (TREE_TYPE (t)) == true

Now the big question. Should it be represented as an signed int in the
tree so that my conversion works or how can I detect that I have to
simulate the wrapping?

I suspect the conversion might happen here:

(gdb) print t.int_cst.common.type.base
$11 = {code = INTEGER_TYPE, side_effects_flag = 0, constant_flag = 0,
addressable_flag = 0, volatile_flag = 0, readonly_flag = 0,
unsigned_flag = 1, ...}
(gdb) print t.type.common.base
$12 = {code = INTEGER_CST, side_effects_flag = 0, constant_flag = 1,
addressable_flag = 0, volatile_flag = 0, readonly_flag = 0,
unsigned_flag = 0, ...}
(gdb) print t.common.type.base
$13 = {code = INTEGER_TYPE, side_effects_flag = 0, constant_flag = 0,
addressable_flag = 0, volatile_flag = 0, readonly_flag = 0,
unsigned_flag = 1, ...}

What is the meaning of the different types. Some have the unsigned_flag
set, others not?

Thanks a lot
Tobias