[PATCH] Assert on invalid bitmap iterations

[Richard Biener]

The following guards against (some) remove-current-bit cases.  It
would have ICEd for PR77855 instead of producing wrong code.

Bootstrap / regtest running on x86_64-unknown-linux-gnu.

Comments?

Thanks,
Richard.

2016-10-06  Richard Biener  <rguent...@suse.de>

        * bitmap.c (bitmap_elem_to_freelist): Set indx to -1.
        * bitmap.h (bmp_iter_set): When advancing to the next element
        check that we didn't remove the current one.
        (bmp_iter_and): Likewise.
        (bmp_iter_and_compl): Likewise.

Index: gcc/bitmap.c
===================================================================
--- gcc/bitmap.c        (revision 240828)
+++ gcc/bitmap.c        (working copy)
@@ -66,6 +66,7 @@ bitmap_elem_to_freelist (bitmap head, bi
   bitmap_obstack *bit_obstack = head->obstack;
 
   elt->next = NULL;
+  elt->indx = -1;
   if (bit_obstack)
     {
       elt->prev = bit_obstack->elements;
Index: gcc/bitmap.h
===================================================================
--- gcc/bitmap.h        (revision 240828)
+++ gcc/bitmap.h        (working copy)
@@ -618,6 +618,9 @@ bmp_iter_set (bitmap_iterator *bi, unsig
          bi->word_no++;
        }
 
+      /* Make sure we didn't remove the element while iterating.  */
+      gcc_checking_assert (bi->elt1->indx != -1);
+
       /* Advance to the next element.  */
       bi->elt1 = bi->elt1->next;
       if (!bi->elt1)
@@ -664,6 +667,9 @@ bmp_iter_and (bitmap_iterator *bi, unsig
       /* Advance to the next identical element.  */
       do
        {
+         /* Make sure we didn't remove the element while iterating.  */
+         gcc_checking_assert (bi->elt1->indx != -1);
+
          /* Advance elt1 while it is less than elt2.  We always want
             to advance one elt.  */
          do
@@ -674,6 +680,9 @@ bmp_iter_and (bitmap_iterator *bi, unsig
            }
          while (bi->elt1->indx < bi->elt2->indx);
 
+         /* Make sure we didn't remove the element while iterating.  */
+         gcc_checking_assert (bi->elt2->indx != -1);
+
          /* Advance elt2 to be no less than elt1.  This might not
             advance.  */
          while (bi->elt2->indx < bi->elt1->indx)
@@ -726,11 +735,17 @@ bmp_iter_and_compl (bitmap_iterator *bi,
          bi->word_no++;
        }
 
+      /* Make sure we didn't remove the element while iterating.  */
+      gcc_checking_assert (bi->elt1->indx != -1);
+
       /* Advance to the next element of elt1.  */
       bi->elt1 = bi->elt1->next;
       if (!bi->elt1)
        return false;
 
+      /* Make sure we didn't remove the element while iterating.  */
+      gcc_checking_assert (bi->elt2->indx != -1);
+
       /* Advance elt2 until it is no less than elt1.  */
       while (bi->elt2 && bi->elt2->indx < bi->elt1->indx)
        bi->elt2 = bi->elt2->next;