[PATCH] [Reassociation] Add support for reassociation with unsafe algebra.

[Chad Rosier]

All,
The purpose of this patch is to add support for reassociation with unsafe
algebra.

I've performed correctness testing on AArch64 with our internal test suite
and saw no correctness regressions. I'm currently running correctness
against ARMv7.

The performance improvements look good, but I'm unable to share the
numbers at this time; I'll see what I can do(, but no promises).

Please have a look!

Chad

http://reviews.llvm.org/D4129