Warning when compiling dwarf2out.c with -ftree-parallelize-loops=4

[Razya Ladelsky]

Hi,

When enabling -ftree-parallelize-loops=4 , bootstrap fails:

cc1: warnings being treated as errors
../../gcc/gcc/dwarf2out.c: In function âdwarf2out_frame_debugâ:
../../gcc/gcc/dwarf2out.c:2393: error: array subscript is above array 
bounds
../../gcc/gcc/dwarf2out.c:2394: error: array subscript is above array 
bounds


The array ref for which the subscript exceeded the boundary is 
regs_saved_in_regs[i].
The array is defined: 
   static GTY(()) struct reg_saved_in_data regs_saved_in_regs[4];
therefore the upper bound of the array regs_saved_in_regs is 3
and the subscript is i.

However, when autopar pass is enabled, 
the following condition is inserted :

if (num_iterations > 400-1)
    { /* parallel code.  */
 
         GOMP_parallel_start
        loopfn ();
         GOMP_parallel_end
         last iteration of the loop; /* accessing the array: 
regs_saved_in_regs[i] */ 
    }
else
   goto serial code

 After VRP propagation, 400 is marked as the up_sub.

 Since VRP can now determine that the array subscript is a constant, the 
check of validity fails.
 
if (TREE_CODE (up_sub) == INTEGER_CST
   && tree_int_cst_lt (up_bound, up_sub)
   && !tree_int_cst_equal (up_bound, up_sub)
  && (!ignore_off_by_one
           || !tree_int_cst_equal (int_const_binop (PLUS_EXPR, up_bound, 
integer_one_node, 0), up_sub))) 
          warning (OPT_Warray_bounds, "%Harray subscript is above array 
bounds",  location);


As far as I get it, there is no real failure here.
Parloop, unaware of the array's upper bound, inserts the 'enough 
iterations' condition (i>400-1), and thereby 
makes the last iteration range from 400 upwards. 
VRP now has a constant it can compare to the array's upper bound.
Correct programs that do not exceed the array bound will now fail because 
VRP is not aware of the 
fact that the parallel code (and last iteration it is looking at) is 
actually not executed in these cases.

I'm not sure how to proceed, in order to avoid this warning.
Any ideas?

Thanks,
Razya