Re: [patch] tree-ssa-dom.c: Use VEC(vrp_element_p,heap) instead ofVARRAY.

[Kazu Hirata <kazu at cs dot umass dot edu>]

Hi Jeff,

> > > This doesn't look right to me.  If you read the comments earlier in the
> > > code it states that two tests must be performed.  First you have to
> > > verify the existance of the varray (or VEC) then you have to look at
> > > the number of active entries.
> > > 
> > > Your change will cause a segfault in the first case as *vrp_records
> > > would be dereferencing a null pointer.
> > > 
> > > So my question to you would be is there some reason why it's no longer
> > > possible for vrp_records to be null?
> > 
> > *vrp_records may be NULL, but VEC_length (vrp_element_p, NULL)
> > evaluates to 0 because VEC_length is implemented as
> You're misunderstanding me.  I'm referring to vrp_records being null,
> not *vrp_records.
> 
> If vrp_records is null, then *vrp_records is going to segfault.

Is your question about this hunk?

@@ -2110,11 +2128,9 @@ simplify_cond_and_lookup_avail_expr (tre
 	    return NULL;
 
 	  vrp_hash_elt_p = (struct vrp_hash_elt *) *slot;
-	  vrp_records = vrp_hash_elt_p->records;
-	  if (vrp_records == NULL)
-	    return NULL;
+	  vrp_records = &vrp_hash_elt_p->records;
 
-	  limit = VARRAY_ACTIVE_SIZE (vrp_records);
+	  limit = VEC_length (vrp_element_p, *vrp_records);
 
 	  /* If we have no value range records for this variable, or we are
 	     unable to extract a range for this condition, then there is

If that's the case, vrp_records could be NULL without my patch.

With my patch, vrp_records cannot be NULL because we have

          slot = htab_find_slot (vrp_data, &vrp_hash_elt, NO_INSERT);
          if (slot == NULL)
	    return NULL;

          /* At this point, SLOT is nonnull.  */
	  vrp_hash_elt_p = (struct vrp_hash_elt *) *slot;
          /* At this point, VRP_HASH_ELT_P is nonnull.  */
	  vrp_records = &vrp_hash_elt_p->records;
          /* At this point, VRP_RECORDS is nonnull.  */

	  limit = VEC_length (vrp_element_p, *vrp_records);

Kazu Hirata