Revert "[InstCombine] Avoid combining the bitcast of a var that is used as...

Revert "[InstCombine] Avoid combining the bitcast of a var that is used as both address and result of load instructions"
Revert "[InstCombine] Combine A->B->A BitCast"

as this appears to cause PR27996 and as discussed in http://reviews.llvm.org/D20847

This reverts commits r270135 and r263734.

llvm-svn: 274094