Re: Strange IV choices?

[Sebastian Pop <sebastian dot pop at cri dot ensmp dot fr>]

On Tue, Dec 14, 2004 at 03:56:32PM +0100, Richard Guenther wrote:
> Hi!
> 
> It seems that ivopts is confused by local copies of objects.
> Suppose you have some complex array managing class, the two
> functionally identical functions
> 
> void arrayAssignManual(const Array<2, double, BrickViewU>& a,
>                        const Array<2, double, BrickViewU>& b,
>                        const Array<2, double, BrickViewU>& c,
>                        const Array<2, double, BrickViewU>& d,
>                        const Interval<2> &I)
> {
>         int ie = I[0].length();
>         int je = I[1].length();
>         for (int j=0; j<je; ++j)
>           for (int i=0; i<ie; ++i)
>             a(i,j) = b(i,j)+c(i,j)+d(i,j);
> }
> 
> and
> 
> void arrayAssignManualCopy(const Array<2, double, BrickViewU>& a_,
>                        const Array<2, double, BrickViewU>& b_,
>                        const Array<2, double, BrickViewU>& c_,
>                        const Array<2, double, BrickViewU>& d_,
>                        const Interval<2> &I)
> {
>         Array<2, double, BrickViewU> a(a_), b(b_), c(c_), d(d_);
>         int ie = I[0].length();
>         int je = I[1].length();
>         for (int j=0; j<je; ++j)
>           for (int i=0; i<ie; ++i)
>             a(i,j) = b(i,j)+c(i,j)+d(i,j);
> }
> 
> get optimized vastly different.  While the first one gets an
> inner loop with
> 


In the second case the analyzer produces a scev_not_known element:

(analyze_scalar_evolution 
  (loop_nb = 1)
  (scalar = ostride_192)
(get_scalar_evolution 
  (scalar = ostride_192)
  (scalar_evolution = ))
(analyze_initial_condition 
  (loop_phi_node = 
ostride_192 = PHI <ostride_362(11), ostride_125(16)>;)
  (init_cond = ostride_125))
(analyze_evolution_in_loop 
  (loop_phi_node = ostride_192 = PHI <ostride_362(11), ostride_125(16)>;)
  (evolution_function = scev_not_known))
(set_scalar_evolution 
  (scalar = ostride_192)
  (scalar_evolution = ostride_192))
)

This situation is generated by the following code:

# ostrideD.165952_5 = PHI <1(0)>;
D.166161_150 = (*dD.166162_151)[1];
ostrideD.165952_125 = ostrideD.165952_5 * D.166161_150;
loop
  # ostrideD.165952_192 = PHI <ostrideD.165952_362(11), ostrideD.165952_125(16)>;
  D.166161_358 = (*dD.166162_356)[1];
  ostrideD.165952_362 = ostrideD.165952_192 * D.166161_358;
endloop

the above code is the same as: 

a = loop-phi (someconstant, a * T[1])

that is an exponential evolution with an undetermined step: T[1], and
these are not handled.