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[Bug middle-end/51994] [4.6/4.7 Regression] git-1.7.8.3 miscompiled due to negative bitpos from get_inner_reference
- From: "rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Thu, 26 Jan 2012 10:01:23 +0000
- Subject: [Bug middle-end/51994] [4.6/4.7 Regression] git-1.7.8.3 miscompiled due to negative bitpos from get_inner_reference
- Auto-submitted: auto-generated
- References: <bug-51994-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51994
--- Comment #19 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-01-26 10:01:23 UTC ---
I agree, all callers of get_inner_reference need to cope with a negative
bitpos. Those that forward it unchecked to functions that expect an
unsigned bitpos are broken.
Thus I think fixing the prototypes is correct. If that exposes other
issues we have to fix them. The issue in extract_split_bit_field
is obviously the same - unsigned prototype and unsigned offset in
while (bitsdone < bitsize)
{
unsigned HOST_WIDE_INT thissize;
rtx part, word;
unsigned HOST_WIDE_INT thispos;
unsigned HOST_WIDE_INT offset;
offset = (bitpos + bitsdone) / unit;
also
thispos = (bitpos + bitsdone) % unit;
might not be correct with a negative (bitpos + bitsdone).
extract_fixed_bit_field has the same prototype issue, so eventually we
want to simply account for them in the callers (if there are less).
Only memory operands may have a negative bitpos and those we should be
able to adjust via adjust_address (but by what amount?) to make bitpos
positive.
So you could say already the routines called from the get_inner_reference
callers should do that.
Eric, you should know this area the best - what do you recommend here?
[we could assert in the unsigned bitpos taking functions that the MSB
is not set on bitpos]