> > May I apply the patch I posted?  It boostrapped/regtested fine on
> > x86-64/Linux.
>
> Yes.

Thanks.  Unfortunately, while this was the last identified problem on x86, 
another issue is visible on x86-64 as a miscompilation of XML/Ada at -O0.
Reduced testcase attached:

 gnat.dg/pack18.adb
 gnat.dg/pack18_pkg.ads

The executable segfaults because it attempts a read at 0x2000000000000000.

The scenario is a follows: Rec is packed record so its fields are bit fields, N 
being at bit offset 129.  The representative is at offset 0.

get_bit_range is invoked on N with a bitpos of 1, because there is variable 
offset and its DECL_FIELD_OFFFSET is added to it instead of bitpos.  Hence

  bitpos - bitoffset

is (unsigned HOST_WIDE_INT) -128.  This value enters unchanged the new code in 
store_bit_field and the division:

     offset = bitregion_start / BITS_PER_UNIT;

yields the problematic big number.

It would therefore appear that bitstart and bitend need to be signed offsets, 
at least until they are adjusted by store_bit_field.

-- 
Eric Botcazou