Only check for PHI uses inside the current loop.

Only check for PHI uses inside the current loop.

Hoisting a value that is used by a PHI in the loop will introduce a
copy because the live range is extended to cross the PHI.

The same applies to PHIs in exit blocks.

Also use this opportunity to make HasLoopPHIUse() non-recursive.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154454 91177308-0d34-0410-b5e6-96231b3b80d8