[Bug middle-end/26643] Linux matroxfb_probe miscompiled

[matz at suse dot de]

------- Comment #9 from matz at suse dot de  2006-03-13 08:57 -------
-fno-ivopts fixes it.  The problem is how bitfield refs are dealt with it
seems.  With -fno-ivopts the final_cleanup pass looks like so at the
interesting point:

  D.2180 = BIT_FIELD_REF <*pdev, 32, 544> & 4294967295;
...
  if ((BIT_FIELD_REF <*b, 32, 0> & 4294967295) != D.2180) goto <L3>;
    else goto <L1>;

ivopts lead to this code at that point:

  D.2180 = BIT_FIELD_REF <*pdev, 32, 544> & 4294967295;
...
  if ((MEM[base: (long unsigned int *) b] & 4294967295) != D.2180) goto <L3>;
    else goto <L1>;

Now BIT_FIELD_REF<*b,32,0> extract exactly the 32 bit at address 'b'.
But MEM[base: (long unsigned int *) b] extracts the 64 bit at that address.
The masking afterwards selects the lower 32bit from that, but ppc being
a big endian target this extracts the wrong half.  Let's CC Zdenek for this.


-- 

matz at suse dot de changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rakdver at gcc dot gnu dot
                   |                            |org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26643