[llvm] r174156 - Revert r174152. The shift amount may overflow and in that case this transformation is illegal.

[Anton Korobeynikov]

> Do we have a test case to ensure that such an illegal transformation
> does not occur?
Probably can be distilled from http://llvm.org/bugs/show_bug.cgi?id=15135

With best regards, Anton Korobeynikov
Faculty of Mathematics and Mechanics, Saint Petersburg State University