Fixed bug with hoisting/deopting in taken-block instead of preheader.

With a fail-before pass-after regression test.

Rationale:
Hoisting and deopting should be done in the taken-block for safety
of the evaluation *unless* the code was in the original loop header,
and thus always taken.

https://code.google.com/p/android/issues/detail?id=198697

bug: 26506884

Change-Id: I1cf121292559fd2570ad67587ec3bc8e8a85a92a