[Bug tree-optimization/79302] [6/7 Regression] ICE in add_loop_constraints, at graphite-sese-to-poly.c:933 building 445.gobmk

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79302

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
But it smells similar to PR77318.

  gcc_assert (!chrec_contains_undetermined (nb_iters));
  nb_iters = scalar_evolution_in_region (region, loop, nb_iters);
  gcc_assert (!chrec_contains_undetermined (nb_iters));

nb_iters is (unsigned int) _2 + 4294967295, defined outside of loop,
loops outer loop is not fully contained within the region.
scalar_evolution_in_region goes

  if (TREE_CODE (t) != SSA_NAME
      || loop_in_sese_p (loop, region))
    /* FIXME: we would need instantiate SCEV to work on a region, and be more
       flexible wrt. memory loads that may be invariant in the region.  */
    return instantiate_scev (before, loop,
                             analyze_scalar_evolution (loop, t));

where analyze_scalar_evolution just does nothing (obviously) but
instantiate_scev returns scev_not_known because in 'before' we have
_2 = middle_39 - bottom_30 and that's not analyzable (but graphite
expects instantiation to stop there, evaluating to this symbolically).

But we do

static tree
instantiate_scev_name (basic_block instantiate_below,
                       struct loop *evolution_loop, struct loop *inner_loop,
                       tree chrec,
                       bool *fold_conversions,
                       int size_expr)
{
...
  /* If the analysis yields a parametric chrec, instantiate the
     result again.  */
  res = analyze_scalar_evolution (def_loop, chrec);

and that fails and we run in circles via

  else if (res != chrec_dont_know)
    {
      if (inner_loop
          && def_bb->loop_father != inner_loop
          && !flow_loop_nested_p (def_bb->loop_father, inner_loop))
        /* ???  We could try to compute the overall effect of the loop here. 
*/
        res = chrec_dont_know;
      else
        res = instantiate_scev_r (instantiate_below, evolution_loop,
                                  inner_loop, res,
                                  fold_conversions, size_expr);

with the same SSA name again and again until we give up due to the recursion
limit.  So the expectation of GRAPHITE is sth like

Index: gcc/tree-scalar-evolution.c
===================================================================
--- gcc/tree-scalar-evolution.c (revision 245058)
+++ gcc/tree-scalar-evolution.c (working copy)
@@ -280,6 +280,7 @@ along with GCC; see the file COPYING3.
 #include "params.h"
 #include "tree-ssa-propagate.h"
 #include "gimple-fold.h"
+#include "cfgexpand.h"

 static tree analyze_scalar_evolution_1 (struct loop *, tree, tree);
 static tree analyze_scalar_evolution_for_address_of (struct loop *loop,
@@ -2460,9 +2461,14 @@ instantiate_scev_name (basic_block insta
        /* ???  We could try to compute the overall effect of the loop here. 
*/
        res = chrec_dont_know;
       else
-       res = instantiate_scev_r (instantiate_below, evolution_loop,
-                                 inner_loop, res,
-                                 fold_conversions, size_expr);
+       {
+         if (res == chrec
+             && is_gimple_assign (SSA_NAME_DEF_STMT (res)))
+           res = gimple_assign_rhs_to_tree (SSA_NAME_DEF_STMT (res));
+         res = instantiate_scev_r (instantiate_below, evolution_loop,
+                                   inner_loop, res,
+                                   fold_conversions, size_expr);
+       }
     }

   /* Store the correct value to the cache.  */

which fixes the ICE.  But we can probably simply deal with this case in
add_loop_constraints with

Index: gcc/graphite-sese-to-poly.c
===================================================================
--- gcc/graphite-sese-to-poly.c (revision 245058)
+++ gcc/graphite-sese-to-poly.c (working copy)
@@ -930,7 +931,11 @@ add_loop_constraints (scop_p scop, __isl
   /* loop_i <= expr_nb_iters */
   gcc_assert (!chrec_contains_undetermined (nb_iters));
   nb_iters = scalar_evolution_in_region (region, loop, nb_iters);
-  gcc_assert (!chrec_contains_undetermined (nb_iters));
+  if (chrec_contains_undetermined (nb_iters))
+    {
+      isl_space_free (space);
+      return domain;
+    }

   isl_pw_aff *aff_nb_iters = extract_affine (scop, nb_iters,
                                             isl_space_copy (space));