[LLVMdev] Reassociate fix for 3.2

[Duncan Sands]

Hi Pawel, can you please pull this fix

http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20121112/155994.html

into the 3.2 branch.  It fixes a crash in the reassociate pass.  I think it
is low risk.

Thanks, Duncan.