The SLP vectorizer should propagate IR-level optimization hints/flags (nsw, nuw, exact, fast-math) when converting scalar instructions into vectors. But this isn't a simple copy - we need to take the intersection (the logical 'and') of the sets of flags on the scalars.
The solution is further complicated because we can have non-uniform (non-SIMD) vector ops after:
http://reviews.llvm.org/D4015
http://llvm.org/viewvc/llvm-project?view=revision&revision=211339
The vast majority of changed files are existing tests that were not propagating IR flags, but I've also added a new test file for focused testing of IR flag possibilities.