[RFC] Wrong "current" pointers with bitmap_ior and bitmap_ior_and_compl

[Kaz Kojima]

Hi,

I've got odd ICEs with some bitmap operations when working on
sh-lra branch.
bitmap_ior and bitmap_ior_and_compl are the bitmap operations
for DST = A | B and DST = A | (B & ~KILL) respectively.  It
looks they could make bitmaps with the wrong "current" pointer.
One small example is

DST: [(bit 0, bit 127), indx=0] <-> [(bit 151), indx=1] -> 0
A:   [(bit 141), indx=1] -> 0
B:   [(bit 142), indx=1] -> 0

where assuming that BITMAP_ELEMENT_ALL_BITS is 128.
In this case, bitmap_ior makes DST into the list

[(bit 141, bit 142), indx=1] <-> [(bit 151), indx=1] -> 0

and unlinks the second element with bitmap_elt_clear_from.
If the "current" pointer of DST pointed the 2nd element,
the current pointer points the element freed from the list:

DST: [(bit 141, bit 142), indx=1] -> 0
DST->current: [(bit 151), indx=1]

even after bitmap_elt_clear_from done.
bitmap_elt_clear_from has the code to fix the current pointer
for the correct list of which elements have strictly ascending
indx values.  It doesn't work for the above list because its
elements have the same indx.
It seems that bitmap_and, bitmap_and_compl and bitmap_xor have
the line to avoid this issue already.  The patch below adds
the same line to bitmap_ior and bitmap_ior_and_compl.
The patch is tested on i686-pc-linux-gnu with bootstrap and
the top level "make -k check".

Regards,
        kaz
--
        * bitmap.c (bitmap_ior): Reset the current pointer before calling
        bitmap_elt_clear_from.
        (bitmap_ior_and_compl): Likewise.

diff --git a/bitmap.c b/bitmap.c
index 8f7f306..ace6aea 100644
--- a/bitmap.c
+++ b/bitmap.c
@@ -1595,6 +1595,8 @@ bitmap_ior (bitmap dst, const_bitmap a, const_bitmap b)
   if (dst_elt)
     {
       changed = true;
+      /* Ensure that dst->current is valid.  */
+      dst->current = dst->first;
       bitmap_elt_clear_from (dst, dst_elt);
     }
   gcc_checking_assert (!dst->current == !dst->first);
@@ -1951,6 +1953,8 @@ bitmap_ior_and_compl (bitmap dst, const_bitmap a, 
const_bitmap b, const_bitmap k
   if (dst_elt)
     {
       changed = true;
+      /* Ensure that dst->current is valid.  */
+      dst->current = dst->first;
       bitmap_elt_clear_from (dst, dst_elt);
     }
   gcc_checking_assert (!dst->current == !dst->first);