Scanning entire basic block may be too expensive in terms of compile time. Instead...

Scanning entire basic block may be too expensive in terms of compile time. Instead, just use whatever location info first non-phi instruction has.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@130729 91177308-0d34-0410-b5e6-96231b3b80d8