[PATCH] Strength reduce intrinsics with overflow into regular arithmetic operations if possible.

[Nadav Rotem]

Everything except for the function WillNotOverflowSignedMul looks great. I also agree with Philip that the refactoring should go in as a separate patch. The first part of WillNotOverflowSignedMul looks correct. The second part (SignBits == BitWidth + 1) is more complex and I prefer that someone else would take a look. I believe that Michael Gottesman is a good candidate for reviewing this part of the code.

http://reviews.llvm.org/D6477