may_be_unaligned_p bug?

[DJ Delorie]

> OK, I'll do some testing with it tomorrow.  Which GCC versions are affected?

I tested trunk and an old 4.2.1 internal branch, and found the bug on
both, so anything in between would be affected too.  It goes back at
least to this patch, which mostly fixed the bug:

2008-02-19  Christian Bruel  <christian.bruel@st.com>
            Zdenek Dvorak  <ook@ucw.cz>

	* tree-ssa-loop-ivopts.c (may_be_unaligned_p): Check step alignment.

(our 4.2.1 branch, plus the above patch, plus your patch, works)