[PATCH]: Fix bug preventing some LICM in PRE

[Daniel Berlin <dberlin at dberlin dot org>]

Steven Bosscher noticed a bug related to PRE where we were marking uses in 
conditionals (and other types of don't care statements) as 
generating things in the TMP_GEN set.
This is not correct, only DEFs go in TMP_GEN.
This genreally showed up as our inability to perform loop invariant motion 
on some things when there were conditionals with them as part of loop 
tests, etc.

Fix + testcase attached.

The vect.exp change is because this patch will cause vect-8[6-8].c to fail 
due to the particular code it wants to see vectorized (k = i + n in the 
below example)

 for (i = 0; i < n; i++)
    {
      for (j = 0; j < n; j++)
        {
          k = i + n;
          a[j] = k;
        }
      b[i] = k;
    }

is completely loop invariant out of both loops, and the fixed PRE will 
happily move it.

I've simply added -fno-tree-pre to the default flags for the vectorizer 
tests for now, since this is supposed to be testing vectorization, not 
general optimization.  This will let vectorizer people test that we 
vectorize whatever they like.

It has been bootstrapped and regtestested on x86_64, ia64-linux, and 
i686-pc-linux-gnu, with no regressions (thanks to steven for submitting 
it to SuSE's autotesters).

Committed to mainline.

--Dan

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