[Bug tree-optimization/40321] [4.4/4.5 Regression] internal compiler error: in compute_antic, at tree-ssa-pre.c:2501

dberlin at dberlin dot org gcc-bugzilla@gcc.gnu.org
Wed Jun 3 15:16:00 GMT 2009 


------- Comment #13 from dberlin at gcc dot gnu dot org  2009-06-03 15:16 -------
Subject: Re:  [4.4/4.5 Regression] internal 
        compiler error: in compute_antic, at tree-ssa-pre.c:2501

Hmmm, clean should only have to check set1 and set2, not AVAIL_OUT.
I'm not sure why it looks at AVAIL_OUT at all, that seems broken to me.

Gotta look at the change history to see what or if i was thinking

In reality, the behavior of translating names only if they have a
leader in the set we are currently translating is correct (or at least
is what the paper does and what "should" work).  Though if there is no
leader, it should actually return NULL_TREE, not keep going.  If there
is no leader for the name in ANTIC, the expression can't be ANTIC
since it's operands aren't ANTIC.  clean is probably removing those
anyway.

Anyway the GVNPRE theory goes:

Names get removed from ANTIC through subtraction of TMP_GEN only.

clean() clean() is a no-op because we do it in topological order
(sorted_array_from_bitmap), and thus are guaranteed to process names
before things dependent on those names.

On Wed, Jun 3, 2009 at 10:00 AM, rguenth at gcc dot gnu dot org
<gcc-bugzilla@gcc.gnu.org> wrote:
>
>
> ------- Comment #12 from rguenth at gcc dot gnu dot org  2009-06-03 14:00 -------
> The problem seems to be the asymmetry wrt handling of NAMEs vs. SSA_NAME
> operands
> in NARYs and REFERENCEs.  We happily translate NAMEs and do not clean them
> if they are in AVAIL_OUT, but we only can translate SSA_NAME operands if they
> have a leader in the set we are currently translating (wtf?) and we clean
> the NARYs and REFERENCEs that do not have their SSA_NAME operands in ANTIC_IN
> itself.
>
> Huh.  Fixing both "fixes" the problem, but obviously results in larger ANTIC_IN
> sets.
>
> @@ -1466,13 +1499,15 @@ phi_translate_1 (pre_expr expr, bitmap_s
>              {
>                unsigned int op_val_id = VN_INFO (newnary.op[i])->value_id;
>                pre_expr leader = find_leader_in_sets (op_val_id, set1, set2);
> -               pre_expr result = phi_translate_1 (leader, set1, set2,
> +               pre_expr result;
> +               if (!leader)
> +                 leader = get_or_alloc_expr_for_name (newnary.op[i]);
> +               result = phi_translate_1 (leader, set1, set2,
>                                                   pred, phiblock, seen);
>                if (result && result != leader)
>                  {
>                    tree name = get_representative_for (result);
> -                   if (!name)
> -                     return NULL;
> +                   gcc_assert (name != NULL_TREE);
>                    newnary.op[i] = name;
>                  }
>                else if (!result)
> @@ -1569,13 +1604,14 @@ phi_translate_1 (pre_expr expr, bitmap_s
>              {
>                unsigned int op_val_id = VN_INFO (op0)->value_id;
>                leader = find_leader_in_sets (op_val_id, set1, set2);
> +               if (!leader)
> +                 leader = get_or_alloc_expr_for_name (op0);
>                opresult = phi_translate_1 (leader, set1, set2,
>                                            pred, phiblock, seen);
>                if (opresult && opresult != leader)
>                  {
>                    tree name = get_representative_for (opresult);
> -                   if (!name)
> -                     break;
> +                   gcc_assert (name != NULL_TREE);
>                    op0 = name;
>                  }
>                else if (!opresult)
> @@ -1587,13 +1623,14 @@ phi_translate_1 (pre_expr expr, bitmap_s
>              {
>                unsigned int op_val_id = VN_INFO (op1)->value_id;
>                leader = find_leader_in_sets (op_val_id, set1, set2);
> +               if (!leader)
> +                 leader = get_or_alloc_expr_for_name (op1);
>                opresult = phi_translate_1 (leader, set1, set2,
>                                            pred, phiblock, seen);
>                if (opresult && opresult != leader)
>                  {
>                    tree name = get_representative_for (opresult);
> -                   if (!name)
> -                     break;
> +                   gcc_assert (name != NULL_TREE);
>                    op1 = name;
>                  }
>                else if (!opresult)
> @@ -1604,13 +1641,14 @@ phi_translate_1 (pre_expr expr, bitmap_s
>              {
>                unsigned int op_val_id = VN_INFO (op2)->value_id;
>                leader = find_leader_in_sets (op_val_id, set1, set2);
> +               if (!leader)
> +                 leader = get_or_alloc_expr_for_name (op2);
>                opresult = phi_translate_1 (leader, set1, set2,
>                                            pred, phiblock, seen);
>                if (opresult && opresult != leader)
>                  {
>                    tree name = get_representative_for (opresult);
> -                   if (!name)
> -                     break;
> +                   gcc_assert (name != NULL_TREE);
>                    op2 = name;
>                  }
>                else if (!opresult)
> @@ -2091,7 +2129,7 @@ clean (bitmap_set_t set, basic_block blo
>
>   for (i = 0; VEC_iterate (pre_expr, exprs, i, expr); i++)
>     {
> -      if (!valid_in_sets (set, NULL, expr, block))
> +      if (!valid_in_sets (set, AVAIL_OUT (block), expr, block))
>        bitmap_remove_from_set (set, expr);
>     }
>   VEC_free (pre_expr, heap, exprs);
>
>
> the fix results in some ICEs because we cannot insert though.
>
> A fix the other way around is be possible as well, but it doesn't fix the
> problem:
>
> Index: tree-ssa-pre.c
> ===================================================================
> --- tree-ssa-pre.c      (revision 148119)
> +++ tree-ssa-pre.c      (working copy)
> @@ -1717,6 +1717,10 @@ phi_translate_1 (pre_expr expr, bitmap_s
>        edge e;
>        gimple def_stmt;
>        tree name = PRE_EXPR_NAME (expr);
> +       unsigned int name_val_id = VN_INFO (name)->value_id;
> +       pre_expr leader = find_leader_in_sets (name_val_id, set1, set2);
> +       if (!leader)
> +         return NULL;
>
>        def_stmt = SSA_NAME_DEF_STMT (name);
>        if (gimple_code (def_stmt) == GIMPLE_PHI
> @@ -2006,7 +2010,7 @@ valid_in_sets (bitmap_set_t set1, bitmap
>   switch (expr->kind)
>     {
>     case NAME:
> -      return bitmap_set_contains_expr (AVAIL_OUT (block), expr);
> +      return union_contains_value (set1, set2, get_expr_value_id (expr));
>     case NARY:
>       {
>        unsigned int i;
>
>
> Note that what is odd is that during clean () we use ANTIC_IN to clean
> expressions but we change it at the same time.  How are we sure that
> clean (); clean () is a no-op?
>
>
> --
>
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40321
>
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>


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